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112 results on '"H. D. Aller"'

1. Stochastic modeling of multiwavelength variability of the classical BL Lac object OJ 287 on timescales ranging from decades to hours

Author: Goyal, A., Stawarz, L., Zola, S., Marchenko, V., Soida, M., Nilsson, K., Ciprini, S., Baran, A., Ostrowski, M., Wiita, P. J., Gopal-Krishna, Siemiginowska, A., Sobolewska, M., Jorstad, S., Marscher, A., Hovatta, M. F. Aller H. D. Aller T., Caton, D. B., Reichart, D., Matsumoto, K., Sadakane, K., Gazeas, K., Kidger, M., Piirola, V., Jermak, H., Alicavus, F., Baliyan, K. S., Baransky, A., Berdyugin, A., Blay, P., Boumis, P., Boyd, D., Bufan, Y., Torrent, M. Campas, Campos, F., Gomez, J. Carrillo, Dalessio, J., Debski, B., Dimitrov, D., Drozdz, M., Er, H., Erdem, A., Perez, A. Escartin, Ramazani, V. Fallah, Filippenko, A. V., Gafton, E., Garcia, F., Godunova, V., Pinilla, F. Gomez, Gopinathan, M., Haislip, J. B., Haque, S., Harmanen, J., Hudec, R., Hurst, G., Ivarsen, K. M., Joshi, A., Kagitani, M., Karaman, N., Karjalainen, R., Kaur, N., l-Wierzbowska, D. Kozie, Kuligowska, E., Kundera, T., Kurowski, S., Kvammen, A., LaCluyze, A. P., Lee, B. C., Liakos, A., de Haro, J. Lozano, Mohammed, I., Moore, J. P., Mugrauer, M., Nogues, R. Naves, Neely, A. W., Ogloza, W., Okano, S., Pajdosz, U., Pandey, J. C., Perri, M., Poyner, G., Provencal, J., Pursimo, T., Raj, A., Rajkumar, B., Reinthal, R., Reynolds, T., Saario, J., Sadegi, S., Sakanoi, T., Gonzalez, J. L. Salto, Sameer, Heung, A., Simon, O., Siwak, M., Schweyer, T., Alfaro, F. C. Soldan, Sonbas, E., Strobl, J., Takalo, L. O., Espasa, L. Tremosa, Valdes, J. R., Vasylenko, V. V., Verrecchia, F., Webb, J. R., Yoneda, M., Zejmo, M., Zheng, W., Zielinski, P., Janik, J., Chavushyan, V., Cheung, C. C., and Giroletti, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present the results of our power spectral density analysis for the BL Lac object OJ\,287, utilizing the {\it Fermi}-LAT survey at high-energy $\gamma$-rays, {\it Swift}-XRT in X-rays, several ground-based telescopes and the {\it Kepler} satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time auto-regressive moving average (CARMA) processes. Owing to the inclusion of the {\it Kepler} data, we were able to construct \emph{for the first time} the optical variability power spectrum of a blazar without any gaps across $\sim6$ dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the $\gamma$-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the {\it Fermi}-LAT data, corresponding to $\sim 150$\,days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise., Comment: ApJ accepted
Published: 2017
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2. Why Haven't Many of the Brightest Radio Loud Blazars Been Detected by Fermi ?

Author: Lister, M. L., Hovatta, M. F. Aller. H. D. Aller. T., Max-Morbeck, W., Readhead, A. C. S., Richards, J. L., and Ros, E.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We use the complete MOJAVE 1.5 Jy sample of active galactic nuclei (AGN) to examine the gamma-ray detection statistics of the brightest radio-loud blazars in the northern sky. We find that 23% of these AGN were not detected above 0.1 GeV by the Fermi LAT during the 4-year 3FGL catalog period partly because of an instrumental selection effect, and partly due to their lower Doppler boosting factors. Blazars with synchrotron peaks in their spectral energy distributions located below $10^{13.4}$ Hz also tend to have high-energy peaks that lie below the 0.1 GeV threshold of the LAT, and are thus less likely to be detected by Fermi. The non-detected AGN in the 1.5 Jy sample also have significantly lower 15 GHz radio modulation indices and apparent jet speeds, indicating that they have lower than average Doppler factors. Since the effective amount of relativistic Doppler boosting is enhanced in gamma-rays (particularly in the case of external inverse-Compton scattering), this makes them less likely to appear in the 3FGL catalog. Based on their observed properties, we have identified several bright radio-selected blazars that are strong candidates for future detection by Fermi., Comment: Accepted for publication in Astrophysical Journal Letters
Published: 2015
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3. Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Author: V M Larionov, S G Jorstad, A P Marscher, M Villata, C M Raiteri, P S Smith, I Agudo, S S Savchenko, D A Morozova, J A Acosta-Pulido, M F Aller, H D Aller, T S Andreeva, A A Arkharov, R Bachev, G Bonnoli, G A Borman, V Bozhilov, P Calcidese, M I Carnerero, D Carosati, C Casadio, W-P Chen, G Damljanovic, A V Dementyev, A Di Paola, A Frasca, A Fuentes, J L Gómez, P Gónzalez-Morales, A Giunta, T S Grishina, M A Gurwell, V A Hagen-Thorn, T Hovatta, S Ibryamov, M Joshi, S Kiehlmann, J-Y Kim, G N Kimeridze, E N Kopatskaya, Yu A Kovalev, Y Y Kovalev, O M Kurtanidze, S O Kurtanidze, A Lähteenmäki, C Lázaro, L V Larionova, E G Larionova, G Leto, A Marchini, K Matsumoto, B Mihov, M Minev, M G Mingaliev, D Mirzaqulov, R V Muñoz Dimitrova, I Myserlis, A A Nikiforova, M G Nikolashvili, N A Nizhelsky, E Ovcharov, L D Pressburger, I A Rakhimov, S Righini, N Rizzi, K Sadakane, A C Sadun, M R Samal, R Z Sanchez, E Semkov, S G Sergeev, L A Sigua, L Slavcheva-Mihova, P Sola, Yu V Sotnikova, A Strigachev, C Thum, E Traianou, Yu V Troitskaya, I S Troitsky, P G Tsybulev, A A Vasilyev, O Vince, Z R Weaver, K E Williamson, and G V Zhekanis
Published: 2020
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4. Opacity, variability, and kinematics of AGN jets

Author: A M Kutkin, I N Pashchenko, K V Sokolovsky, Y Y Kovalev, M F Aller, and H D Aller
Published: 2019
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5. A Ring Accelerator? Unusual Jet Dynamics in the IceCube Candidate PKS 1502+106

Author: S Britzen, M Zajacek, L C Popovic, C Fendt, A Tramacere, I N Pashchenko, F Jaron, R Panis, L Petrov, M F Aller, and H D Aller
Subjects: Astrophysics
Abstract: On 2019/07/30.86853 UT, IceCube detected a high-energy astrophysical neutrino can-didate. The Flat Spectrum Radio Quasar PKS 1502+106 is located within the 50 percent uncertainty region of the event. Our analysis of 15 GHz Very Long Baseline Ar-ray (VLBA) and astrometric 8 GHz VLBA data, in a time span prior and after theIceCube event, reveals evidence for a radio ring structure which develops with time.Several arc-structures evolve perpendicular to the jet ridge line. We find evidence forprecession of a curved jet based on kinematic modelling and a periodicity analysis.An outflowing broad line region (BLR) based on the C IV line emission (Sloan Dig-ital Sky Survey, SDSS) is found. We attribute the atypical ring to an interaction ofthe precessing jet with the outflowing material.We discuss our findings in thecontext of a spine-sheath scenario where the ring reveals the sheath andits interaction with the surroundings (NLR clouds).We find that the radioemission is correlated with theγ-ray emission, with radio lagging theγ-rays. Basedon theγ-ray variability timescale, we constrain theγ-ray emission zone to the BLR(30-200rg) and within the jet launching region. We discuss that the outflowing BLRprovides the external radiation field forγ-ray production via external Compton scat-tering.The neutrino is most likely produced by proton-proton interactionin the blazar zone (beyond the BLR), enabled by episodic encounters ofthe jet with dense clouds, i.e. some molecular cloud in the NLR.
Published: 2021
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6. MOJAVE XXI. Decade-long linear polarization variability in AGN jets at parsec scales

Author: D I Zobnina, H D Aller, M F Aller, D C Homan, Y Y Kovalev, M L Lister, I N Pashchenko, A B Pushkarev, and T Savolainen
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: Using stacking of images obtained at different epochs, we studied the variability properties of linear polarization of active galactic nucleus (AGN) jets on parsec-scales. Our sample is drawn from the MOJAVE programme, and consists of 436 AGNs manifesting core-jet morphology and having at least five VLBA observing epochs at 15 GHz from January 1996 through August 2019, with some additional archival VLBA data reduced by us. We employed a stacking procedure and constructed maps of (i) standard deviation of fractional polarization and electric vector position angle (EVPA) over epochs as the measure of variability and (ii) median polarization degree to quantify typical values in time. The distributions of these values along and across the jet were analysed for the whole sample for the first time. We found that core EVPA variability is typically higher than that of the jet, presumably due to component blending and outflow bends in the core. The BL Lacertae object cores have lower EVPA variability, compared to that of quasars, possibly due to lower Faraday rotation measure, suggesting a stronger ordered magnetic field component. The EVPA becomes more stable down the jet. Most of the sources showing this trend have a time coverage of more than 12 years and at least 15 epochs. The possible cause could be the increase of stability in the magnetic field direction, reflecting an increase in the fraction of the magnetic field that is ordered. There are no significant optical-class-dependent or spectral-class-dependent relations in the EVPA variability properties in AGN jets., 15 pages, 11 figures, 5 tables; accepted by MNRAS; full electronic tables are available as ancillary files
Published: 2023
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7. MOJAVE – XX. Persistent linear polarization structure in parsec-scale AGN jets

Author: A B Pushkarev, H D Aller, M F Aller, D C Homan, Y Y Kovalev, M L Lister, I N Pashchenko, T Savolainen, D I Zobnina, Crimean Astrophysical Observatory, University of Michigan, Ann Arbor, Denison University, RAS - P.N. Lebedev Physics Institute, Purdue University, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), polarization, general [quasars], Space and Planetary Science, general [BL Lacertae objects], Astrophysics of Galaxies (astro-ph.GA), active [galaxies], jets [galaxies], FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, galaxies [radio continuum]
Abstract: We analysed the parsec-scale linear polarization properties of 436 active galactic nuclei (AGN) based on 15 GHz polarimetric Very Long Baseline Array (VLBA) observations. We present polarization and total intensity images averaged over at least five epochs since 1996 January 19 through 2019 August 4. Stacking improves the image sensitivity down to $\sim$30 $\mu$Jy/beam and effectively fills out the jet cross-section both in total intensity and linear polarization. It delineates the long-term persistent magnetic field configuration and its regularity by restoring spatial distributions of the electric vector position angle (EVPA) and fractional polarization, respectively. On average, about ten years of stacking period is needed to reveal the stable and most-complete polarization distribution of a source. We find that the degree of polarization significantly increases down and across the jet towards its edges, typically manifesting U or W-shaped transverse profiles, suggesting a presence of a large-scale helical magnetic field associated with the outflow. In some AGN jets, mainly BL Lacs, we detect quasi-constant fractional polarization profiles across the jet, accompanied by EVPAs that closely follow the outflow. BL Lacs show higher fractional polarization values in their cores and jets than those in quasars up to hectoparsec de-projected scales, while on larger scales, they become comparable. High-synchrotron-peaked BL Lac jets are found to be less polarized than intermediate and low-synchrotron-peaked BL Lacs. The spatial distribution of the EVPAs in BL Lacs tend to align with the local jet direction, while quasars show an excess of orthogonal polarization orientation., Comment: 18 pages, 16 figures, 5 tables; accepted by MNRAS; full electronic tables, animated movie and all Figure Set plots are available as ancillary files
Published: 2023

8. Identifying changing jets through their radio variability

Author: Ioannis Liodakis, Talvikki Hovatta, Mark Gurwell, H. D. Aller, Margo F. Aller, Anne Lähteenmäki, Merja Tornikoski, University of Turku, Metsähovi Radio Observatory, University of Michigan, Ann Arbor, Harvard University, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Supermassive black hole, Jet (fluid), 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Relativistic processes, FOS: Physical sciences, Astronomy and Astrophysics, Context (language use), Astrophysics, Jets [Galaxies], 01 natural sciences, Active [Galaxies], symbols.namesake, Relativistic beaming, Astrophysical jet, Space and Planetary Science, 0103 physical sciences, symbols, Radio frequency, Relativistic quantum chemistry, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Doppler effect
Abstract: Supermassive black holes launch highly relativistic jets with velocities reaching Lorentz factors as high as $\Gamma>50$. How the jets accelerate to such high velocities and where along the jet do they reach terminal velocity are open questions that are tightly linked to their structure, launching and dissipation mechanisms. Changes in the beaming factor along the jets could potentially reveal jet acceleration, deceleration, or bending. We aim to (1) quantify the relativistic effects in multiple radio frequencies and (2) study possible jet velocity--viewing angle variations at parsec scales. We used the state-of-the-art code Magnetron to model light curves from the University of Michigan Radio Observatory and the Mets\"{a}hovi Radio Observatory's monitoring programs in five frequencies covering about 25 years of observations in the 4.8-37~GHz range for 61 sources. We supplement our data set with high-frequency radio observations in the 100-340~GHz range from ALMA, CARMA, and SMA. For each frequency we estimate the Doppler factor which we use to quantify possible changes in the relativistic effects along the jets. The majority of our sources do not show any statistically significant difference in their Doppler factor across frequencies. This is consistent with constant velocity in a conical jet, as expected at parsec scales. However, our analysis reveals 17 sources where relativistic beaming changes as a function of frequency. In the majority of cases the Doppler factor increases towards lower frequencies. Only 1253-053 shows the opposite behavior. By exploring their jet properties we find that the jet of 0420-014 is likely bent across the 4.8-340~GHz range. For 0212+735 the jet is likely parabolic, and still accelerating in the 4.8-37~GHz range. We discuss possible interpretations for the trends found in the remaining sources., Comment: 15 pages, 5 figure, 3 Tables, accepted for publication in A&A
Published: 2021

9. Non-stationary emission of the blazar S4 0954+658 over a wide range of wavelength

Author: M. G. Larionov, G. Pooley, L. N. Volvach, Anne Lähteenmäki, E. Recillas, Merja Tornikoski, V. V. Vlasyuk, N. S. Kardashev, A. Porras, L. Carrasco, O. I. Spiridonova, A. E. Volvach, V. S. Bychkova, H. D. Aller, and M. F. Aller
Subjects: Physics, Active galactic nucleus, ta115, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Radio astronomy observatory, Wavelength, Radio observatory, Space and Planetary Science, Observatory, 0103 physical sciences, Range (statistics), Blazar, 010303 astronomy & astrophysics, Fermi Gamma-ray Space Telescope
Abstract: Data from long-term multi-frequency monitoring are used to analyze variations in the flux density of the active galactic nucleus S4 0954+658. These data were obtained at the CrimeanAstrophysical Observatory, the Metsahovi Radio Observatory of Aalto University, the University of Michigan Radio Astronomy Observatory, the Cavendish Laboratory of Cambridge University, the Special Astrophysical Observatory, and the National Institute of Astrophysics, Optics, and Electronics; 0.1–300-GeV data from the Fermi space gamma-ray observatory were also used. Radio data at 4.8, 8, 14.5, 15, 22.2, and 36.8 GHz are considered together with optical and near-infrared data in the R, J, H, and K filters.
Published: 2016

10. Physical characteristics of the Blazar AO 0235+164

Author: H. D. Aller, L. N. Volvach, M. G. Larionov, Mahito Sasada, Anne Lähteenmäki, Merja Tornikoski, M. F. Aller, and A. E. Volvach
Subjects: Physics, education.field_of_study, Supermassive black hole, ta115, Active galactic nucleus, ta213, ta114, Astrophysics::High Energy Astrophysical Phenomena, ta221, Population, ta1171, Binary number, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Wavelength, Space and Planetary Science, Elliptical galaxy, Binary system, ta216, education, Blazar, Astrophysics::Galaxy Astrophysics
Abstract: Long series of multi-frequency monitoring data of the active galactic nucleus (AGN) AO 0235+164 from the radio to the gamma-ray are analyzed. AO 0235+164 may be a close binary system comprised of two supermassive black holes (SMBHs). A harmonic analysis has established the presence of orbital and precessional periods of two and eight years, respectively. These values are close to the analogous periods found in other AGNs that have been proposed to be close SMBH binary systems in a stage of their evolution close to coalescence. A cross-correlation analysis is used to find the time delay between corresponding flares occurring in different wavebands. The empirical dependence found earlier for a number of other AGNS relating the delay in the flux variations with the frequency is observed for this object, and has the form of an inverse logarithmic dependence, providing evidence that the flux variability of AGNs at centimeter and shorter wavelengths is intrinsic. The standard picture of jet activity of AGNs supposes plasma formations that move from the central regions along outflows, becoming optically thin at longer and longer wavelengths as they do so. The physical and dynamical characteristics of AO 0235+164 suggest it is a close binary with SMBHs with similar masses of the order of 1010M⊙. This is one of the most massive systems of two SMBHs. The velocities of the companion and central black hole about their common center of mass are estimated to be 104 and 5×103 km/s. The results obtained suggest that observed bright AGNs form a relatiavely rare population among massive elliptical galaxies, due to their narrowly directed emission and their short lifetimes.
Published: 2015
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11. Long-term, multi-frequency monitoring of the blazar S0528+134 (Nimfa)

Author: A. E. Volvach, A. M. Kutkin, Mahito Sasada, A. Lakhteenmaki, Joni Tammi, H. D. Aller, M. G. Larionov, L. N. Volvach, M. F. Aller, Merja Tornikoski, and P. Savolainen
Subjects: Physics, Supermassive black hole, ta115, ta213, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, law.invention, Wavelength, Space and Planetary Science, law, Observatory, Precession, Radio frequency, Blazar, Flare
Abstract: Flux-density variations of the quasar S0528+134 (Nimfa) are analyzed based on long-term monitoring at five radio frequencies between 4.8 and 37 GHz, performed at the Crimean Astrophysical Observatory, the Metsahovi Radio Observatory of Aalto University, and the University of Michigan Radio Astronomy Observatory. The dynamics of a powerful flare in 1996 are analyzed using gamma-ray (0.1–300 GeV), X-ray (2–10 keV, 15–50 keV), and radio observations. The delays of the flare between different spectral ranges and between different radio wavelengths have been measured. The dependence for the delays at different radio wavelengths relative to the X-ray and optical flares is established based on long-term observations in the X-ray, optical, and radio obtained from 2004 to 2013. Multi-frequency monitoring in the radio is used to estimate the orbital and precession periods in the binary supermassive black hole system S0528+134 and the physical characteristics of this system.
Published: 2014
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12. Stochastic modeling of multiwavelength variability of the classical BL Lac object OJ 287 on timescales ranging from decades to hours

Author: A. Goyal, Ł. Stawarz, S. Zola, V. Marchenko, M. Soida, K. Nilsson, S. Ciprini, A. Baran, M. Ostrowski, P. J. Wiita, null Gopal-Krishna, A. Siemiginowska, M. Sobolewska, S. Jorstad, A. Marscher, M. F. Aller, H. D. Aller, T. Hovatta, D. B. Caton, D. Reichart, K. Matsumoto, K. Sadakane, K. Gazeas, M. Kidger, V. Piirola, H. Jermak, F. Alicavus, K. S. Baliyan, A. Baransky, A. Berdyugin, P. Blay, P. Boumis, D. Boyd, Y. Bufan, M. Campas Torrent, F. Campos, J. Carrillo Gómez, J. Dalessio, B. Debski, D. Dimitrov, M. Drozdz, H. Er, A. Erdem, A. Escartin Pérez, V. Fallah Ramazani, A. V. Filippenko, E. Gafton, F. Garcia, V. Godunova, F. Gómez Pinilla, M. Gopinathan, J. B. Haislip, S. Haque, J. Harmanen, R. Hudec, G. Hurst, K. M. Ivarsen, A. Joshi, M. Kagitani, N. Karaman, R. Karjalainen, N. Kaur, D. Kozieł-Wierzbowska, E. Kuligowska, T. Kundera, S. Kurowski, A. Kvammen, A. P. LaCluyze, B. C. Lee, A. Liakos, J. Lozano de Haro, J. P. Moore, M. Mugrauer, R. Naves Nogues, A. W. Neely, W. Ogloza, S. Okano, U. Pajdosz, J. C. Pandey, M. Perri, G. Poyner, J. Provencal, T. Pursimo, A. Raj, B. Rajkumar, R. Reinthal, T. Reynolds, J. Saario, S. Sadegi, T. Sakanoi, J. L. Salto González, null Sameer, A. O. Simon, M. Siwak, T. Schweyer, F. C. Soldán Alfaro, E. Sonbas, J. Strobl, L. O. Takalo, L. Tremosa Espasa, J. R. Valdes, V. V. Vasylenko, F. Verrecchia, J. R. Webb, M. Yoneda, M. Zejmo, W. Zheng, P. Zielinski, J. Janik, V. Chavushyan, I. Mohammed, C. C. Cheung, and M. Giroletti
Subjects: ACTIVE GALACTIC NUCLEI, Astrophysics::High Energy Astrophysical Phenomena, OJ-287, FOS: Physical sciences, Astrophysics, individual: OJ 287 [BL Lacertae objects], Type (model theory), Astronomy & Astrophysics, magnetic fields, 01 natural sciences, LARGE-AREA TELESCOPE, Radio telescope, PERIODICITIES, 0103 physical sciences, individual (OJ 287) [BL Lacertae objects], Blazar, 010303 astronomy & astrophysics, LACERTAE OBJECTS, acceleration of particles, MISSION, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Science & Technology, 010308 nuclear & particles physics, OPTICAL POLARIZATION, Spectral density, Astronomy and Astrophysics, Light curve, non-thermal [radiation mechanisms], BLAZARS, 13. Climate action, Space and Planetary Science, Colors of noise, Physical Sciences, active [galaxies], UNEQUALLY-SPACED DATA, Astrophysics - High Energy Astrophysical Phenomena, OJ 287, Noise (radio), BL Lac object
Abstract: We present the results of our power spectral density analysis for the BL Lac object OJ\,287, utilizing the {\it Fermi}-LAT survey at high-energy $\gamma$-rays, {\it Swift}-XRT in X-rays, several ground-based telescopes and the {\it Kepler} satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time auto-regressive moving average (CARMA) processes. Owing to the inclusion of the {\it Kepler} data, we were able to construct \emph{for the first time} the optical variability power spectrum of a blazar without any gaps across $\sim6$ dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the $\gamma$-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the {\it Fermi}-LAT data, corresponding to $\sim 150$\,days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise., Comment: ApJ accepted
Published: 2017
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13. A prolonged flare in the blazar 3C 454.3

Author: M. F. Aller, H. D. Aller, L. N. Volvach, Anne Lähteenmäki, A. E. Volvach, Joni Tammi, Merja Tornikoski, M. G. Larionov, Jonathan León-Tavares, Emilia Järvelä, and A. M. Kutkin
Subjects: Physics, Supermassive black hole, Orbital plane, ta115, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Orbital period, law.invention, Black hole, Binary black hole, Space and Planetary Science, law, Astrophysics::Earth and Planetary Astrophysics, Blazar, Schwarzschild radius, Flare
Abstract: We present an analysis of data from multi-frequency monitoring of the blazar 3C 454.3 in 2010–2012, when the source experienced an unusually prolonged flare with a duration of about two years. This corresponds to the orbital period of the companion in a scenario in which two supermassive black holes are present in the nucleus of 3C 454.3. The flare’s shape, duration, and amplitude can be explained as a result of precession, if the plane of the accretion disk and the orbital plane of the binary are coincident. We detected small-scale structure of the flare, on time scales of no more than a month. These features probably correspond to inhomogeneities in the accretion disk and surrounding regions, with sizes of the order of 1015 cm. We estimated the size of the accretion disk based on the dynamical and geometrical parameters of this binary system: its diameter is comparable to the size of the orbit of the supermassive binary black hole, and its thickness does not exceed the gravitational radius of the central black hole. The presence of characteristic small-scale features during the flare makes it possible to estimate the relative time delays of variations in different spectral ranges: from gamma-ray to millimeter wavelengths.
Published: 2013
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14. A new method for estimating frequency-dependent core shifts in active galactic nucleus jets

Author: Denise C. Gabuzda, Nadia Kudryavtseva, H. D. Aller, and Margo F. Aller
Subjects: Physics, Jet (fluid), Active galactic nucleus, Opacity, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Quasar, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 7. Clean energy, Magnetic field, Core (optical fiber), Space and Planetary Science, Very-long-baseline interferometry, Astrophysics::Galaxy Astrophysics
Abstract: We discuss the opacity in the core regions of active galactic nuclei observed with Very Long Baseline Interferometry (VLBI), and describe a new method for deriving the frequency-dependent shifts of the VLBI core from the frequency-dependent time lags of flares observed with single-dish observations. Application of the method to the core shifts of the quasar 3C 345 shows a very good agreement between the core shifts directly measured from VLBI observations and derived from flares in the total flux density using the proposed method. The frequency-dependent time lags of flares can be used to derive physical parameters of the jets, such as distance from the VLBI core to the base of the jet and the magnetic fields in the core region. Our estimates for 3C 345 indicate core magnetic fields ~0.1 G and magnetic field at 1 pc ~0.4 G.
Published: 2011
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15. Evolution of flux density and parsec-scale structure of compact extragalactic radio sources from monitoring results at 4.8–36.8 GHz and imaging on the basis of geodetic VLBI observations

Author: L. N. Volvach, Alexander B. Pushkarev, A.E. Volvach, H. D. Aller, and M. F. Aller
Subjects: Physics, Basis (linear algebra), Very-long-baseline interferometry, Scale structure, Geodetic datum, Astrophysics, Parsec
Published: 2009
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16. Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006–2007 outburst

Author: C. M. Raiteri, M. Villata, V. M. Larionov, M. F. Aller, U. Bach, M. Gurwell, O. M. Kurtanidze, A. Lähteenmäki, K. Nilsson, A. Volvach, H. D. Aller, A. A. Arkharov, R. Bachev, A. Berdyugin, M. Böttcher, C. S. Buemi, P. Calcidese, E. Cozzi, A. Di Paola, M. Dolci, J. H. Fan, E. Forné, L. Foschini, A. C. Gupta, V. A. Hagen-Thorn, L. Hooks, T. Hovatta, M. Joshi, M. Kadler, G. N. Kimeridze, T. S. Konstantinova, A. Kostov, T. P. Krichbaum, L. Lanteri, L. V. Larionova, C.-U. Lee, P. Leto, E. Lindfors, F. Montagni, R. Nesci, E. Nieppola, M. G. Nikolashvili, J. Ohlert, A. Oksanen, E. Ovcharov, P. Pääkkönen, M. Pasanen, T. Pursimo, J. A. Ros, E. Semkov, L. A. Sigua, R. L. Smart, A. Strigachev, L. O. Takalo, K. Torii, I. Torniainen, M. Tornikoski, C. Trigilio, H. Tsunemi, G. Umana, and A. Valcheva
Subjects: Physics, Time delays, Brightness, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Phase (waves), FOS: Physical sciences, Flux, Astronomy and Astrophysics, Astrophysics, Light curve, Synchrotron, law.invention, Wavelength, Space and Planetary Science, law, Blazar
Abstract: The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the radio and optical bands. Moreover, an extra emission component contributing to the UV and soft X-ray flux was detected, whose nature is not yet clear. A predicted optical outburst was observed in late 2006/early 2007. We here present the radio-to-optical WEBT light curves during the outburst, together with UV data acquired by Swift in the same period. We found the optical outburst to be as strong as the big outbursts of the past: starting from late September 2006, a brightness increase of 5 mag led to the outburst peak in February 19-21, 2007. We also observed an outburst at mm and then at cm wavelengths, with an increasing time delay going toward lower frequencies during the rising phase. Cross-correlation analysis indicates that the 1 mm and 37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2 months, respectively. These short time delays suggest that the corresponding jet emitting regions are only slightly separated and/or misaligned. In contrast, during the outburst decreasing phase the flux faded contemporaneously at all cm wavelengths. This abrupt change in the emission behaviour may suggest the presence of some shutdown mechanism of intrinsic or geometric nature. The behaviour of the UV flux closely follows the optical and near-IR one. By separating the synchrotron and extra component contributions to the UV flux, we found that they correlate, which suggests that the two emissions have a common origin., Comment: 9 pages, 7 figures, in press for Astronomy and Astrophysics
Published: 2008
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17. Why Have Many of the Brightest Radio-loud Blazars Not Been Detected in Gamma-Rays by Fermi?

Author: M. L. Lister, M. F. Aller, H. D. Aller, T. Hovatta, W. Max-Moerbeck, A. C. S. Readhead, J. L. Richards, E. Ros, Aalto-yliopisto, and Aalto University
Subjects: Astrofísica, Active galactic nucleus, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, jets [galaxies], Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, general [gamma-ray burst], 7. Clean energy, 01 natural sciences, law.invention, symbols.namesake, law, 0103 physical sciences, Blazar, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common, Physics, general [quasars], 010308 nuclear & particles physics, Scattering, Spectral density, Astronomy and Astrophysics, galaxies [radio continuum], Synchrotron, 13. Climate action, Space and Planetary Science, Sky, active [galaxies], Astronomia, symbols, Doppler effect, Fermi Gamma-ray Space Telescope
Abstract: We use the complete MOJAVE 1.5 Jy sample of active galactic nuclei (AGNs) to examine the gamma-ray detection statistics of the brightest radio-loud blazars in the northern sky. We find that 23% of these AGNs were not detected above 0.1 GeV by the Fermi-LAT during the four-year 3FGL catalog period partly because of an instrumental selection effect and partly due to their lower Doppler boosting factors. Blazars with synchrotron peaks in their spectral energy distributions located below 10^(13.4) Hz also tend to have high-energy peaks that lie below the 0.1 GeV threshold of the LAT, and are thus less likely to be detected by Fermi. The non-detected AGNs in the 1.5 Jy sample also have significantly lower 15 GHz radio modulation indices and apparent jet speeds, indicating that they have lower than average Doppler factors. Since the effective amount of relativistic Doppler boosting is enhanced in gamma-rays (particularly in the case of external inverse-Compton scattering), this makes them less likely to appear in the 3FGL catalog. Based on their observed properties, we have identified several bright radio-selected blazars that are strong candidates for future detection by Fermi.
Published: 2015

18. Synchrotron flaring in the jet of 3C 279

Author: Jamie Stevens, Marc Türler, Esko Valtaoja, Margo F. Aller, Elina Lindfors, M. Villata, H. D. Aller, Gino Tosti, C. M. Raiteri, Merja Tornikoski, and D. Mazin
Subjects: Physics, Shock wave, Jet (fluid), 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Flux, Astronomy and Astrophysics, Quasar, Astrophysics, 01 natural sciences, Synchrotron, law.invention, Space and Planetary Science, law, 0103 physical sciences, Very-long-baseline interferometry, Astrophysics::Solar and Stellar Astrophysics, Blazar, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Line (formation)
Abstract: We study the synchrotron flaring behaviour of the blazar 3C279 based on an extensive dataset covering 10 years of monitoring at 19 different frequencies in the radio-to-optical range. The properties of a typical outburst are derived from the observations by decomposing the 19 lightcurves into a series of self-similar events. This analysis is achieved by fitting all data simultaneously to a succession of outbursts defined according to the shock-in-jet model of Marscher & Gear (1985). We compare the derived properties of the synchrotron outbursts in 3C279 to those obtained with a similar method for the quasar 3C273. It is argued that differences in the flaring behaviour of these two sources are intrinsic to the sources themselves rather than being due to orientation effects. We also compare the start times and flux densities of our modelled outbursts with those measured from radio components identified in Very Long Baseline Interferometry (VLBI) images. We find VLBI counterparts for most of our model outbursts, although some high-frequency peaking events are not seen in the radio maps. Finally, we study the link between the appearance of a new synchrotron component and the EGRET gamma-ray state of the source at 10 different epochs. We find that an early-stage shock component is always present during high gamma-ray states, while in low gamma-ray states the time since the onset of the last synchrotron outburst is significantly longer. This statistically significant correlation supports the idea that gamma-ray flares are associated with the early stages of shock components propagating in the jet. We note, however, that the shock wave is already beyond the broad line region during the gamma-ray flaring., 10 pages, 5 figures, accepted for publication in A&A
Published: 2006
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19. Multiwavelength observations of Mrk 501 in 2008

Author: MAGIC Collaboration, J. Aleksić(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. Ansoldi(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), L. A. Antonelli(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Antoranz(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), A. Babic(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), P. Bangale(Max-Planck-Institut für Physik, D-80805 München, Germany), U. Barres de Almeida(Max-Planck-Institut für Physik, D-80805 München, Germany), J. A. Barrio(Universidad Complutense, E-28040 Madrid, Spain), J. Becerra González(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), W. Bednarek(University of Lodz, PL-90236 Lodz, Poland), K. Berger(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), E. Bernardini(Deutsches Elektronen-Synchrotron), A. Biland(ETH Zurich, CH-8093 Zurich, Switzerland), O. Blanch(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), R. K. Bock(Max-Planck-Institut für Physik, D-80805 München, Germany), S. Bonnefoy(Universidad Complutense, E-28040 Madrid, Spain), G. Bonnoli(INAF National Institute for Astrophysics, I-00136 Rome, Italy), F. Borracci(Max-Planck-Institut für Physik, D-80805 München, Germany), T. Bretz(Universität Würzburg, D-97074 Würzburg, Germany), E. Carmona(Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, Spain), A. Carosi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), D. Carreto Fidalgo(Universität Würzburg, D-97074 Würzburg, Germany), P. Colin(Max-Planck-Institut für Physik, D-80805 München, Germany), E. Colombo(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), J. L. Contreras(Universidad Complutense, E-28040 Madrid, Spain), J. Cortina(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. Covino(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Da Vela(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), F. Dazzi(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), A. De Angelis(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), G. De Caneva(Deutsches Elektronen-Synchrotron), B. De Lotto(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), C. Delgado Mendez(Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, Spain), M. Doert(Technische Universität Dortmund, D-44221 Dortmund, Germany), A. Domínguez(Inst. de Astrofísica de Andalucía), D. Dominis Prester(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Dorner(Universität Würzburg, D-97074 Würzburg, Germany), M. Doro(Università di Padova and INFN, I-35131 Padova, Italy), S. Einecke(Technische Universität Dortmund, D-44221 Dortmund, Germany), D. Eisenacher(Universität Würzburg, D-97074 Würzburg, Germany), D. Elsaesser(Universität Würzburg, D-97074 Würzburg, Germany), E. Farina(Università dell'Insubria, Como, I-22100 Como, Italy), D. Ferenc(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), M. V. Fonseca(Universidad Complutense, E-28040 Madrid, Spain), L. Font(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), K. Frantzen(Technische Universität Dortmund, D-44221 Dortmund, Germany), C. Fruck(Max-Planck-Institut für Physik, D-80805 München, Germany), R. J. García López(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), M. Garczarczyk(Deutsches Elektronen-Synchrotron), D. Garrido Terrats(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), M. Gaug(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), G. Giavitto(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), N. Godinović(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), A. González Muñoz(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. R. Gozzini(Deutsches Elektronen-Synchrotron), A. Hadamek(Technische Universität Dortmund, D-44221 Dortmund, Germany), D. Hadasch(Institut de Ciències de l'Espai), A. Herrero(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), D. Hildebrand(ETH Zurich, CH-8093 Zurich, Switzerland), J. Hose(Max-Planck-Institut für Physik, D-80805 München, Germany), D. Hrupec(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), W. Idec(University of Lodz, PL-90236 Lodz, Poland), V. Kadenius(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), H. Kellermann(Max-Planck-Institut für Physik, D-80805 München, Germany), M. L. Knoetig(ETH Zurich, CH-8093 Zurich, Switzerland), J. Krause(Max-Planck-Institut für Physik, D-80805 München, Germany), J. Kushida(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. La Barbera(INAF National Institute for Astrophysics, I-00136 Rome, Italy), D. Lelas(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), N. Lewandowska(Universität Würzburg, D-97074 Würzburg, Germany), E. Lindfors(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), S. Lombardi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), M. López(Universidad Complutense, E-28040 Madrid, Spain), R. López-Coto(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), A. López-Oramas(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), E. Lorenz(Max-Planck-Institut für Physik, D-80805 München, Germany), I. Lozano(Universidad Complutense, E-28040 Madrid, Spain), M. Makariev(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), K. Mallot(Deutsches Elektronen-Synchrotron), G. Maneva(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), N. Mankuzhiyil(2,*), K. Mannheim(Universität Würzburg, D-97074 Würzburg, Germany), L. Maraschi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), B. Marcote(Universitat de Barcelona), M. Mariotti(Università di Padova and INFN, I-35131 Padova, Italy), M. Martínez(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), D. Mazin(Max-Planck-Institut für Physik, D-80805 München, Germany), U. Menzel(Max-Planck-Institut für Physik, D-80805 München, Germany), M. Meucci(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), J. M. Miranda(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), R. Mirzoyan(Max-Planck-Institut für Physik, D-80805 München, Germany), A. Moralejo(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), P. Munar-Adrover(Universitat de Barcelona), D. Nakajima(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. Niedzwiecki(University of Lodz, PL-90236 Lodz, Poland), K. Nilsson(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), N. Nowak(Max-Planck-Institut für Physik, D-80805 München, Germany), R. Orito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. Overkemping(Technische Universität Dortmund, D-44221 Dortmund, Germany), S. Paiano(Università di Padova and INFN, I-35131 Padova, Italy), M. Palatiello(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), D. Paneque(6,*), R. Paoletti(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), J. M. Paredes(Universitat de Barcelona), X. Paredes-Fortuny(Universitat de Barcelona), S. Partini(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), M. Persic(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), F. Prada(Inst. de Astrofísica de Andalucía), P. G. Prada Moroni(Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy), E. Prandini(Università di Padova and INFN, I-35131 Padova, Italy), S. Preziuso(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), I. Puljak(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), R. Reinthal(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), W. Rhode(Technische Universität Dortmund, D-44221 Dortmund, Germany), M. Ribó(Universitat de Barcelona), J. Rico(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), J. Rodriguez Garcia(Max-Planck-Institut für Physik, D-80805 München, Germany), S. Rügamer(Universität Würzburg, D-97074 Würzburg, Germany), A. Saggion(Università di Padova and INFN, I-35131 Padova, Italy), T. Saito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), K. Saito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), M. Salvati(INAF National Institute for Astrophysics, I-00136 Rome, Italy), K. Satalecka(7,*), V. Scalzotto(Università di Padova and INFN, I-35131 Padova, Italy), V. Scapin(Universidad Complutense, E-28040 Madrid, Spain), C. Schultz(Università di Padova and INFN, I-35131 Padova, Italy), T. Schweizer(Max-Planck-Institut für Physik, D-80805 München, Germany), S. N. Shore(Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy), A. Sillanpää(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), J. Sitarek(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), I. Snidaric(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Sobczynska(University of Lodz, PL-90236 Lodz, Poland), F. Spanier(Universität Würzburg, D-97074 Würzburg, Germany), V. Stamatescu(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), A. Stamerra(INAF National Institute for Astrophysics, I-00136 Rome, Italy), T. Steinbring(Universität Würzburg, D-97074 Würzburg, Germany), J. Storz(Universität Würzburg, D-97074 Würzburg, Germany), S. Sun(Max-Planck-Institut für Physik, D-80805 München, Germany), T. Surić(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), L. Takalo(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), F. Tavecchio(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Temnikov(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), T. Terzić(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Tescaro(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), M. Teshima(Max-Planck-Institut für Physik, D-80805 München, Germany), J. Thaele(Technische Universität Dortmund, D-44221 Dortmund, Germany), O. Tibolla(Universität Würzburg, D-97074 Würzburg, Germany), D. F. Torres(Institut de Ciències de l'Espai), T. Toyama(Max-Planck-Institut für Physik, D-80805 München, Germany), A. Treves(Università dell'Insubria, Como, I-22100 Como, Italy), M. Uellenbeck(Technische Universität Dortmund, D-44221 Dortmund, Germany), P. Vogler(ETH Zurich, CH-8093 Zurich, Switzerland), R. M. Wagner(Max-Planck-Institut für Physik, D-80805 München, Germany), F. Zandanel(Inst. de Astrofísica de Andalucía), R. Zanin(Universitat de Barcelona), VERITAS Collaboration(Deutsches Elektronen-Synchrotron), (Deutsches Elektronen-Synchrotron), B. Behera(Deutsches Elektronen-Synchrotron), M. Beilicke(Department of Physics, Washington University, St. Louis, MO 63130, USA), W. Benbow(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), R. Bird(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), A. Bouvier(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), V. Bugaev(Department of Physics, Washington University, St. Louis, MO 63130, USA), M. Cerruti(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), X. Chen(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), L. Ciupik(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), E. Collins-Hughes(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), W. Cui(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), C. Duke(Department of Physics, Grinnell College, Grinnell, IA 50112-1690, USA), J. Dumm(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), A. Falcone(Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA), S. Federici(now at GRAPPA Institute, University of Amsterdam, 1098XH), Q. Feng(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), J. P. Finley(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), L. Fortson(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), A. Furniss(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), N. Galante(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), G. H. Gillanders(School of Physics, National University of Ireland Galway, University Road, Galway, Ireland), S. Griffin(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), S. T. Griffiths(Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA), J. Grube(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), G. Gyuk(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), D. Hanna(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), J. Holder(Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA), C. A. Johnson(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), P. Kaaret(Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA), M. Kertzman(Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA), D. Kieda(Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA), H. Krawczynski(Department of Physics, Washington University, St. Louis, MO 63130, USA), M. J. Lang(School of Physics, National University of Ireland Galway, University Road, Galway, Ireland), A. S Madhavan(Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA), G. Maier(Deutsches Elektronen-Synchrotron), P. Majumdar(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), K. Meagher(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), P. Moriarty(Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland), R. Mukherjee(Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA), D. Nieto(Physics Department, Columbia University, New York, NY 10027, USA), A. O'Faoláin de Bhróithe(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), R. A. Ong(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), A. N. Otte(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), A. Pichel(Instituto de Astronomia y Fisica del Espacio, Casilla de Correo 67 - Sucursal 28), M. Pohl(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), A. Popkow(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), H. Prokoph(Deutsches Elektronen-Synchrotron), J. Quinn(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), J. Rajotte(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), G. Ratliff(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), L. C. Reyes(Physics Department, California Polytechnic State University, San Luis Obispo, CA 94307, USA), P. T. Reynolds(Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Ireland), G. T. Richards(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), E. Roache(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), G. H. Sembroski(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), K. Shahinyan(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), F. Sheidaei(Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA), A. W. Smith(Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA), D. Staszak(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), I. Telezhinsky(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), M. Theiling(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), J. Tyler(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), A. Varlotta(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), S. Vincent(Deutsches Elektronen-Synchrotron), S. P. Wakely(Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA), T. C. Weekes(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), R. Welsing(Deutsches Elektronen-Synchrotron), D. A. Williams(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), A. Zajczyk(Department of Physics, Washington University, St. Louis, MO 63130, USA), B. Zitzer(Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA), External Collaborators(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), (INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), M. Villata(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), C. M. Raiteri(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), M. Ajello(Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA), M. Perri(ASI-Science Data Center, Via del Politecnico, I-00133 Rome, Italy), H. D. Aller(Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA), M. F. Aller(Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA), V. M. Larionov(Astron. Inst., St.-Petersburg State Univ., Russia), N. V. Efimova(Astron. Inst., St.-Petersburg State Univ., Russia), T. S. Konstantinova(Astron. Inst., St.-Petersburg State Univ., Russia), E. N. Kopatskaya(Astron. Inst., St.-Petersburg State Univ., Russia), W. P. Chen(Graduate Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan), E. Koptelova(Graduate Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan), H. Y. Hsiao(Graduate Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan), O. M. Kurtanidze(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), M. G. Nikolashvili(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), G. N. Kimeridze(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), B. Jordan(School of Cosmic Physics, Dublin Institute For Advanced Studies, Ireland), P. Leto(INAF - Osservatorio Astrofisico di Catania, Italy), C. S. Buemi(INAF - Osservatorio Astrofisico di Catania, Italy), C. Trigilio(INAF - Osservatorio Astrofisico di Catania, Italy), G. Umana(INAF - Osservatorio Astrofisico di Catania, Italy), A. Lahtenmaki(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), E. Nieppola(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), M. Tornikoski(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), J. Sainio(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), M. Giroletti(INAF Istituto di Radioastronomia, 40129 Bologna, Italy), A. Cesarini(University of Trento, Department of Physics, I38050 Povo, Trento, Italy), L. Fuhrmann(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), Yu. A. Kovalev(Astro Space Center of the Lebedev Physical Institute, 117997), Y. Y. Kovalev(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), Anne Lähteenmäki Group, Department of Radio Science and Engineering, Aalto-yliopisto, Aalto University, Universitat de Barcelona, School services, ELEC, and ~
Subjects: extragalactic background light, Ciencias Físicas, Flux, Electron, Astrophysics, 7. Clean energy, law.invention, purl.org/becyt/ford/1 [https], Raigs gamma, bl lacertae objects, law, individual: Mrk 501 [BL Lacertae objects], Physics, High Energy Astrophysical Phenomena (astro-ph.HE), astro-ph.HE, 213 Electronic, automation and communications engineering, electronics, Astroparticle physics, BL Lacertae objects: individual: Mrk 501, Gamma rays: general, Astronomy and Astrophysics, Space and Planetary Science, Synchrotron, individual: Mrk 50 [BL Lacertae objects], Homogeneous, astroparticle physics, Spectral energy distribution, Electrónica, Física nuclear, Electricidad, Astrophysics - High Energy Astrophysical Phenomena, CIENCIAS NATURALES Y EXACTAS, 1171 Geosciences, Astrophysics::High Energy Astrophysical Phenomena, emitting electrons, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 114 Physical sciences, bl lacertae objects: individual: mrk 501, crab-nebula, Blazar, Astrophysics::Galaxy Astrophysics, tev blazars, variability, 221 Nanotechnology, Gamma rays, Individual: Mrk 501, Institut für Physik und Astronomie, purl.org/becyt/ford/1.3 [https], gamma rays: general, Galaxies, gamma-ray emission, telescope system, Galàxies, Active Galaxies, blazars, gamma-rays, Mrk 501, Astronomía, Crab Nebula, x-ray, 115 Astronomy and space science, Low emission, 216 Materials engineering, Galàxies actives, active galactic nuclei, Active galaxies, ddc:520, general [gamma rays]
Abstract: Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. Our goal is to characterize in detail the source gamma-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE gamma-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity., Comment: Accepted for publication in A&A
Published: 2015
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20. The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies

Author: MAGIC Collaboration, J. Aleksić(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. Ansoldi(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), L. A. Antonelli(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Antoranz(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), A. Babic(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), P. Bangale(Max-Planck-Institut für Physik, D-80805 München, Germany), U. Barres de Almeida(Max-Planck-Institut für Physik, D-80805 München, Germany), J. A. Barrio(Universidad Complutense, E-28040 Madrid, Spain), J. Becerra González(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), W. Bednarek(University of Lodz, PL-90236 Lodz, Poland), K. Berger(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), E. Bernardini(Deutsches Elektronen-Synchrotron), A. Biland(ETH Zurich, CH-8093 Zurich, Switzerland), O. Blanch(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), R. K. Bock(Max-Planck-Institut für Physik, D-80805 München, Germany), S. Bonnefoy(Universidad Complutense, E-28040 Madrid, Spain), G. Bonnoli(INAF National Institute for Astrophysics, I-00136 Rome, Italy), F. Borracci(Max-Planck-Institut für Physik, D-80805 München, Germany), T. Bretz(Universität Würzburg, D-97074 Würzburg, Germany), E. Carmona(Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, Spain), A. Carosi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), D. Carreto Fidalgo(Universität Würzburg, D-97074 Würzburg, Germany), P. Colin(Max-Planck-Institut für Physik, D-80805 München, Germany), E. Colombo(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), J. L. Contreras(Universidad Complutense, E-28040 Madrid, Spain), J. Cortina(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. Covino(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Da Vela(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), F. Dazzi(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), A. De Angelis(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), G. De Caneva(Deutsches Elektronen-Synchrotron), B. De Lotto(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), C. Delgado Mendez(Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, Spain), M. Doert(Technische Universität Dortmund, D-44221 Dortmund, Germany), A. Domínguez(Inst. de Astrofísica de Andalucía), D. Dominis Prester(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Dorner(Universität Würzburg, D-97074 Würzburg, Germany), M. Doro(Università di Padova and INFN, I-35131 Padova, Italy), S. Einecke(Technische Universität Dortmund, D-44221 Dortmund, Germany), D. Eisenacher(Universität Würzburg, D-97074 Würzburg, Germany), D. Elsaesser(Universität Würzburg, D-97074 Würzburg, Germany), E. Farina(Università dell'Insubria, Como, I-22100 Como, Italy), D. Ferenc(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), M. V. Fonseca(Universidad Complutense, E-28040 Madrid, Spain), L. Font(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), K. Frantzen(Technische Universität Dortmund, D-44221 Dortmund, Germany), C. Fruck(Max-Planck-Institut für Physik, D-80805 München, Germany), R. J. García López(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), M. Garczarczyk(Deutsches Elektronen-Synchrotron), D. Garrido Terrats(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), M. Gaug(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), G. Giavitto(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), N. Godinović(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), A. González Mu\ noz(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. R. Gozzini(Deutsches Elektronen-Synchrotron), A. Hadamek(Technische Universität Dortmund, D-44221 Dortmund, Germany), D. Hadasch(Institut de Ciències de l'Espai), A. Herrero(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), D. Hildebrand(ETH Zurich, CH-8093 Zurich, Switzerland), J. Hose(Max-Planck-Institut für Physik, D-80805 München, Germany), D. Hrupec(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), W. Idec(University of Lodz, PL-90236 Lodz, Poland), V. Kadenius(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), H. Kellermann(Max-Planck-Institut für Physik, D-80805 München, Germany), M. L. Knoetig(ETH Zurich, CH-8093 Zurich, Switzerland), J. Krause(Max-Planck-Institut für Physik, D-80805 München, Germany), J. Kushida(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. La Barbera(INAF National Institute for Astrophysics, I-00136 Rome, Italy), D. Lelas(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), N. Lewandowska(Universität Würzburg, D-97074 Würzburg, Germany), E. Lindfors(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), F. Longo(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), S. Lombardi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), M. López(Universidad Complutense, E-28040 Madrid, Spain), R. López-Coto(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), A. López-Oramas(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), E. Lorenz(Max-Planck-Institut für Physik, D-80805 München, Germany), I. Lozano(Universidad Complutense, E-28040 Madrid, Spain), M. Makariev(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), K. Mallot(Deutsches Elektronen-Synchrotron), G. Maneva(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), N. Mankuzhiyil(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), K. Mannheim(Universität Würzburg, D-97074 Würzburg, Germany), L. Maraschi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), B. Marcote(Universitat de Barcelona), M. Mariotti(Università di Padova and INFN, I-35131 Padova, Italy), M. Martínez(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), D. Mazin(Max-Planck-Institut für Physik, D-80805 München, Germany), U. Menzel(Max-Planck-Institut für Physik, D-80805 München, Germany), M. Meucci(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), J. M. Miranda(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), R. Mirzoyan(Max-Planck-Institut für Physik, D-80805 München, Germany), A. Moralejo(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), P. Munar-Adrover(Universitat de Barcelona), D. Nakajima(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. Niedzwiecki(University of Lodz, PL-90236 Lodz, Poland), K. Nilsson(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), N. Nowak(6,32,*), R. Orito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. Overkemping(Technische Universität Dortmund, D-44221 Dortmund, Germany), S. Paiano(Università di Padova and INFN, I-35131 Padova, Italy), M. Palatiello(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), D. Paneque(6,*), R. Paoletti(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), J. M. Paredes(Universitat de Barcelona), X. Paredes-Fortuny(Universitat de Barcelona), S. Partini(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), M. Persic(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), F. Prada(Inst. de Astrofísica de Andalucía), P. G. Prada Moroni(Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy), E. Prandini(Università di Padova and INFN, I-35131 Padova, Italy), S. Preziuso(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), I. Puljak(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), R. Reinthal(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), W. Rhode(Technische Universität Dortmund, D-44221 Dortmund, Germany), M. Ribó(Universitat de Barcelona), J. Rico(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), J. Rodriguez Garcia(Max-Planck-Institut für Physik, D-80805 München, Germany), S. Rügamer(Universität Würzburg, D-97074 Würzburg, Germany), A. Saggion(Università di Padova and INFN, I-35131 Padova, Italy), K. Saito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), M. Salvati(INAF National Institute for Astrophysics, I-00136 Rome, Italy), K. Satalecka(Universidad Complutense, E-28040 Madrid, Spain), V. Scalzotto(Università di Padova and INFN, I-35131 Padova, Italy), V. Scapin(Universidad Complutense, E-28040 Madrid, Spain), C. Schultz(Università di Padova and INFN, I-35131 Padova, Italy), T. Schweizer(Max-Planck-Institut für Physik, D-80805 München, Germany), S. N. Shore(Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy), A. Sillanpää(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), J. Sitarek(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), I. Snidaric(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Sobczynska(University of Lodz, PL-90236 Lodz, Poland), F. Spanier(Universität Würzburg, D-97074 Würzburg, Germany), V. Stamatescu(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), A. Stamerra(INAF National Institute for Astrophysics, I-00136 Rome, Italy), T. Steinbring(Universität Würzburg, D-97074 Würzburg, Germany), J. Storz(Universität Würzburg, D-97074 Würzburg, Germany), S. Sun(Max-Planck-Institut für Physik, D-80805 München, Germany), T. Surić(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), L. Takalo(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), F. Tavecchio(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Temnikov(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), T. Terzić(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Tescaro(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), M. Teshima(Max-Planck-Institut für Physik, D-80805 München, Germany), J. Thaele(Technische Universität Dortmund, D-44221 Dortmund, Germany), O. Tibolla(Universität Würzburg, D-97074 Würzburg, Germany), D. F. Torres(Institut de Ciències de l'Espai), T. Toyama(Max-Planck-Institut für Physik, D-80805 München, Germany), A. Treves(Università dell'Insubria, Como, I-22100 Como, Italy), M. Uellenbeck(Technische Universität Dortmund, D-44221 Dortmund, Germany), P. Vogler(ETH Zurich, CH-8093 Zurich, Switzerland), R. M. Wagner(Max-Planck-Institut für Physik, D-80805 München, Germany), F. Zandanel(Inst. de Astrofísica de Andalucía), R. Zanin(Universitat de Barcelona), VERITAS collaboration(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), (Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), S. Archambault(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), B. Behera(Deutsches Elektronen-Synchrotron), M. Beilicke(Department of Physics, Washington University, St. Louis, MO 63130, USA), W. Benbow(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), R. Bird(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), J. H. Buckley(Department of Physics, Washington University, St. Louis, MO 63130, USA), V. Bugaev(Department of Physics, Washington University, St. Louis, MO 63130, USA), M. Cerruti(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), X. Chen(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), L. Ciupik(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), E. Collins-Hughes(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), W. Cui(Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA), J. Dumm(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), J. D. Eisch(Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA), A. Falcone(Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA), S. Federici(DESY, Platanenallee 6, 15738 Zeuthen, Germany), Q. Feng(Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA), J. P. Finley(Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA), H. Fleischhack(Deutsches Elektronen-Synchrotron), P. Fortin(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA), L. Fortson(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), A. Furniss(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), S. Griffin(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), S. T. Griffiths(Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA), J. Grube(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), G. Gyuk(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), D. Hanna(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), J. Holder(Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA), G. Hughes(Deutsches Elektronen-Synchrotron), T. B. Humensky(Physics Department, Columbia University, New York, NY 10027, USA), C. A. Johnson(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), P. Kaaret(Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA), M. Kertzman(Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA), Y. Khassen(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), D. Kieda(Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA), H. Krawczynski(Department of Physics, Washington University, St. Louis, MO 63130, USA), F. Krennrich(Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA), S. Kumar(Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA), M. J. Lang(School of Physics, National University of Ireland Galway, University Road, Galway, Ireland), G. Maier(Deutsches Elektronen-Synchrotron), S. McArthur(Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA), K. Meagher(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), P. Moriarty(Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland), R. Mukherjee(Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA), R. A. Ong(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), A. N. Otte(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), N. Park(Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA), A. Pichel(Instituto de Astronomia y Fisica del Espacio, Casilla de Correo 67 - Sucursal 28), M. Pohl(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), A. Popkow(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), H. Prokoph(Deutsches Elektronen-Synchrotron), J. Quinn(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), K. Ragan(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), J. Rajotte(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), P. T. Reynolds(Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Ireland), G. T. Richards(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), E. Roache(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), A. C. Rovero(Instituto de Astronomia y Fisica del Espacio, Casilla de Correo 67 - Sucursal 28), G. H. Sembroski(Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA), K. Shahinyan(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), D. Staszak(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), I. Telezhinsky(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), M. Theiling(Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA), J. V. Tucci(Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA), J. Tyler(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), A. Varlotta(Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA), S. P. Wakely(Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA), T. C. Weekes(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), A. Weinstein(Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA), R. Welsing(Deutsches Elektronen-Synchrotron), A. Wilhelm(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), D. A. Williams(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), B. Zitzer(Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA), External collaborators(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), (INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), M. Villata(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), C. Raiteri(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), H. D. Aller(Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA), M. F. Aller(Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA), W. P. Chen(Graduate Institute of Astronomy, National Central University, Jhongli 32054, Taiwan), B. Jordan(School of Cosmic Physics, Dublin Institute for Advanced Studies, Dublin, 2, Ireland), E. Koptelova(Graduate Institute of Astronomy, National Central University, Jhongli 32054, Taiwan), O. M. Kurtanidze(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), A. Lähteenmäki(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), B. McBreen(University College Dublin, Belfield, Dublin 4, Ireland), V. M. Larionov(Isaac Newton Institute of Chile, St. Petersburg Branch, St. Petersburg, Russia), C. S. Lin(Graduate Institute of Astronomy, National Central University, Jhongli 32054, Taiwan), M. G. Nikolashvili(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), E. Angelakis(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), M. Capalbi(ASI-Science Data Center, Via del Politecnico, I-00133 Rome, Italy), A. Carrami\ nana(Instituto Nacional de Astrofísica, Óptica y Electrónica, Tonantzintla, Puebla 72840, Mexico), L. Carrasco(Instituto Nacional de Astrofísica, Óptica y Electrónica, Tonantzintla, Puebla 72840, Mexico), P. Cassaro(INAF Istituto di Radioastronomia, Sezione di Noto, Contrada Renna Bassa, 96017 Noto), A. Cesarini(Department of Physics, University of Trento, I38050, Povo, Trento, Italy), L. Fuhrmann(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), M. Giroletti(INAF Istituto di Radioastronomia, 40129 Bologna, Italy), T. Hovatta(Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125), T. P. Krichbaum(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), H. A. Krimm(Astro Space Center of the Lebedev Physical Institute, 117997 Moscow, Russia), W. Max-Moerbeck(Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125), J. W. Moody(Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, USA), G. Maccaferri(INAF Istituto di Radioastronomia, Stazione Radioastronomica di Medicina, I-40059 Medicina), Y. Mori(Department of Physics, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551, Japan), I. Nestoras(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), A. Orlati(INAF Istituto di Radioastronomia, Stazione Radioastronomica di Medicina, I-40059 Medicina), C. Pace(Indiana University, Department of Astronomy, Swain Hall West 319, Bloomington, IN 47405-7105, USA), R. Pearson(Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, USA), M. Perri(INAF National Institute for Astrophysics, I-00136 Rome, Italy), A. C. S. Readhead(Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125), J. L. Richards(Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907), A. C. Sadun(Department of Physics, University of Colorado, Denver, CO 80220, USA), T. Sakamoto(Department of Physics and Mathematics, College of Science and 952 Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuoku, Sagamihara-shi Kanagawa 252-5258, Japan), J. Tammi(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), M. Tornikoski(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), Y. Yatsu(Department of Physics, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551, Japan), A. Zook(Department of Physics and Astronomy, Pomona College, Claremont CA 91711-6312, USA), Aleksić, J, Ansoldi, Stefano, Antonelli, L. A., Antoranz, P., Babic, A., Bangale, P., Barres De Almeida, U., Barrio, J. A., Becerra González, J., Bednarek, W., Berger, K., Bernardini, E., Biland, A., Blanch, O., Bock, R. K., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Carmona, E., Carosi, A., Carreto Fidalgo, D., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Da Vela, P., Dazzi, F., De Angelis, A., De Caneva, G., De Lotto, B., Delgado Mendez, C., Doert, M., Domínguez, A., Dominis Prester, D., Dorner, D., Doro, M., Einecke, S., Eisenacher, D., Elsaesser, D., Farina, E., Ferenc, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., García López, R. J., Garczarczyk, M., Garrido Terrats, D., Gaug, M., Giavitto, G., Godinović, N., González Muñoz, A., Gozzini, S. R., Hadamek, A., Hadasch, D., Herrero, A., Hildebrand, D., Hose, J., Hrupec, D., Idec, W., Kadenius, V., Kellermann, H., Knoetig, M. L., Krause, J., Kushida, J., La Barbera, A., Lelas, D., Lewandowska, N., Lindfors, E., Longo, Francesco, Lombardi, S., López, M., López Coto, R., López Oramas, A., Lorenz, E., Lozano, I., Makariev, M., Mallot, K., Maneva, G., Mankuzhiyil, N., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, M., Mazin, D., Menzel, U., Meucci, M., Miranda, J. M., Mirzoyan, R., Moralejo, A., Munar Adrover, P., Nakajima, D., Niedzwiecki, A., Nilsson, K., Nowak, N., Orito, R., Overkemping, A., Paiano, S., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Paredes Fortuny, X., Partini, S., Persic, M., Prada, F., Prada Moroni, P. G., Prandini, E., Preziuso, S., Puljak, I., Reinthal, R., Rhode, W., Ribó, M., Rico, J., Rodriguezgarcia, J., Rügamer, S., Saggion, A., Saito, K., Salvati, M., Satalecka, K., Scalzotto, V., Scapin, V., Schultz, C., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Spanier, F., Stamatescu, V., Stamerra, A., Steinbring, T., Storz, J., Sun, S., Surić, T., Takalo, L., Tavecchio, F., Temnikov, P., Terzić, T., Tescaro, D., Teshima, M., Thaele, J., Tibolla, O., Torres, D. F., Toyama, T., Treves, A., Uellenbeck, M., Vogler, P., Wagner, R. M., Zandanel, F., Zanin, R., Archambault, S., Behera, B., Beilicke, M., Benbow, W., Bird, R., Buckley, J. H., Bugaev, V., Cerruti, M., Chen, X., Ciupik, L., Collins Hughes, E., Cui, W., Dumm, J., Eisch, J. D., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., Mcarthur, S., Meagher, K., Moriarty, P., Mukherjee, R., Ong, R. A., Otte, A. N., Park, N., Pichel, A., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Theiling, M., Tucci, J. V., Tyler, J., Varlotta, A., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Wilhelm, A., Williams, D. A., Zitzer, B., Villata, M., Raiteri, C., Aller, H. D., Aller, M. F., Chen, W. P., Jordan, B., Koptelova, E., Kurtanidze, O. M., Lähteenmäki, A., Mcbreen, B., Larionov, V. M., Lin, C. S., Nikolashvili, M. G., Angelakis, E., Capalbi, M., Carramiñana, A., Carrasco, L., Cassaro, P., Cesarini, A., Fuhrmann, L., Giroletti, M., Hovatta, T., Krichbaum, T. P., Krimm, H. A., Max Moerbeck, W., Moody, J. W., Maccaferri, G., Mori, Y., Nestoras, I., Orlati, A., Pace, C., Pearson, R., Perri, M., Readhead, A. C. S., Richards, J. L., Sadun, A. C., Sakamoto, T., Tammi, J., Tornikoski, M., Yatsu, Y., Zook, A., Department of Radio Science and Engineering, Aalto-yliopisto, Aalto University, and Universitat de Barcelona
Subjects: Astrofísica, Brightness, Ciencias Físicas, blazars, Astrophysics, telescope, x-ray variability, 01 natural sciences, Spectral line, BL Lacertae objects, individual, Mrk 421, purl.org/becyt/ford/1 [https], Raigs gamma, emission, MAGIC (telescope), 010303 astronomy & astrophysics, Physics, astro-ph.HE, High Energy Astrophysical Phenomena (astro-ph.HE), individual: Mrk 421 [BL Lacertae objects], Galaxies: BL Lacertae objects: individual: Markarian 421, Spectral energy distribution, Electrónica, Electricidad, Astrophysics - High Energy Astrophysical Phenomena, CIENCIAS NATURALES Y EXACTAS, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Context (language use), Astrophysics::Cosmology and Extragalactic Astrophysics, power spectra, BL Lacertae object, tev photons, 0103 physical sciences, Nucli galàctic actiu, bl lacertae objects: individual: mrk 421, Blazar, Astronomy and Astrophysics, Space and Planetary Science, Active galactic nuclei, 010308 nuclear & particles physics, light curves, Gamma rays, Institut für Physik und Astronomie, purl.org/becyt/ford/1.3 [https], Light curve, Galaxies, Galàxies, Astronomía, Crab Nebula, optical variability, active galactic nuclei, Galàxies actives, Active galaxies, markarian-421, ddc:520
Abstract: We performed a 4.5-month multi-instrument campaign (from radio to VHE gamma rays) on Mrk421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical/UV and X-rays extending over the duration of the campaign. The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multi-wavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk421 during non-flaring activity. Such a temporally extended X-ray/VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies., Comment: Accepted for publication in A&A, 18 pages, 14 figures (v2 has a small modification in the acknowledgments, and also corrects a typo in the field "author" in the metadata)
Published: 2015
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21. AGILE detection of intense gamma-ray emission from the blazar PKS 1510-089

Author: C. Pittori, T. Froysland, A. Pellizzoni, Alessio Trois, Margo F. Aller, H. D. Aller, F. Boffelli, Filippo D'Ammando, Marco Feroci, D. Zanello, Luigi Pacciani, G. Pucella, F. Perotti, Fulvio Gianotti, C. M. Raiteri, A. Rappoldi, E. Vallazza, E. Del Monte, Francesco Longo, A. W. Chen, G. De Paris, V. Cocco, Francesco Lazzarotto, Y. Evangelista, Marco Tavani, S. Cutini, G. Di Cocco, M. Prest, Sergio Colafrancesco, M. Villata, L. A. Antonelli, Sandro Mereghetti, P. W. Cattaneo, I. Donnarumma, A. Argan, M. Fiorini, Massimo Rapisarda, D. Carosati, P. Lipari, Andrea Bulgarelli, Dario Gasparrini, F. Fuschino, Enrico Costa, Martino Marisaldi, V. Vittorini, Valeri M. Larionov, M. Trifoglio, A. Giuliani, I. Lapshov, A. Morselli, P. A. Caraveo, Claudio Labanti, M. Galli, Piergiorgio Picozza, F. Verrecchia, L. Salotti, A. Zambra, Guido Barbiellini, R. Ligustri, Paolo Giommi, S. Vercellone, Paolo Soffitta, G., Pucella, V., Vittorini, F., D'Ammando, M., Tavani, C. M., Raiteri, M., Villata, A., Argan, G., Barbiellini, F., Boffelli, A., Bulgarelli, P., Caraveo, P. W., Cattaneo, A. W., Chen, V., Cocco, E., Costa, E., Delmonte, G. D., Pari, G. D., Cocco, I., Donnarumma, Y., Evangelista, M., Feroci, M., Fiorini, T., Froysland, F., Fuschino, M., Galli, F., Gianotti, A., Giuliani, C., Labanti, I., Lapshov, F., Lazzarotto, P., Lipari, Longo, Francesco, M., Marisaldi, S., Mereghetti, A., Morselli, L., Pacciani, A., Pellizzoni, F., Perotti, P., Picozza, M., Prest, M., Rapisarda, A., Rappoldi, P., Soffitta, M., Trifoglio, A., Troi, E., Vallazza, S., Vercellone, A., Zambra, D., Zanello, L. A., Antonelli, S., Colafrancesco, S., Cutini, D., Gasparrini, P., Giommi, C., Pittori, F., Verrecchia, L., Salotti, M. F., Aller, H. D., Aller, D., Carosati, V. M., Larionov, R., Ligustri, Pucella G, Vittorini V, DAmmando F, Tavani M, Raiteri CM, Villata M, Argan A, Barbiellini G, Boffelli F, Bulgarelli A, Caraveo P, Cattaneo PW, Chen AW, Cocco V, Costa E, DelMonte E, De Paris G, Di Cocco G, Donnarumma I, Evangelista Y, Feroci M, Fiorini M, Froysland T, Fuschino F, Galli M, Gianotti F, Giuliani A, Labanti C, Lapshov I, Lazzarotto F, Lipari P, Longo F, Marisaldi M, Mereghetti S, Morselli A, Pacciani L, Pellizzoni A, Perotti F, Picozza P, Prest M, Rapisarda M, Rappoldi A, Soffitta P, Trifoglio M, Trois A, Vallazza E, Vercellone S, Zambra A, Zanello D, Antonelli LA, Colafrancesco S, Cutini S, Gasparrini D, Giommi P, Pittori C, Verrecchia F, Salotti L, Aller MF, Aller HD, Carosati D, Larionov VM, and Ligustri R
Subjects: High Energy Gamma-ray Astronomy, Active Galactic Nuclei, AGILE satellite, Photon, Astrophysics::High Energy Astrophysical Phenomena, satellite, FOS: Physical sciences, Astrophysics, Photon energy, law.invention, Telescope, AGILE, law, gamma ray satellite, quasar, Blazar, Physics, Astrophysics (astro-ph), Gamma ray, Astronomy and Astrophysics, Quasar, gamma rays: observations -- radiation mechanisms: non-thermal -- quasars: individual: PKS 1510-089, Space and Planetary Science, Spectral energy distribution, Flare
Abstract: We report the detection by the AGILE (Astro-rivelatore Gamma a Immagini LEggero) satellite of an intense gamma-ray flare from the source AGL J1511-0909, associated with the powerful quasar PKS 1510-089, during ten days of observations from 23 August to 1 September 2007. During the observation period, the source was in optical decrease following a flaring event monitored by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). The simultaneous gamma-ray, optical, and radio coverage allows us to study the spectral energy distribution and the theoretical models based on the synchrotron and inverse Compton (IC) emission mechanisms. AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV - 50 GeV and 18 - 60 keV bands, respectively. Between 23 and 27 August 2007, AGILE detected gamma-ray emission from PKS 1510-089 when this source was located about 50 degrees off-axis, with an average flux of (270 +/- 65) x 10^{-8} photons cm^{-2} s^{-1} for photon energy above 100 MeV. In the following period, 28 August - 1 September, after a satellite re-pointing, AGILE detected the source at about 35 degrees off-axis, with an average flux (E > 100 MeV) of (195 +/- 30) x 10^{-8} photons cm^{-2} s^{-1}. No emission was detected by Super-AGILE, with a 3-sigma upper limit of 45 mCrab in 200 ksec. The spectral energy distribution is modelled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions by external photons: the SSC emission contributes primarily to the X-ray band, whereas the contribution of the IC from the external disc and the broad line region match the hard gamma-ray spectrum observed., 5 pages, 5 figures, accepted for publication in A&A
Published: 2008
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22. A multifrequency analysis of radio variability of blazars

Author: C. Bongardo, S. Urpo, H. D. Aller, Margo F. Aller, G. de Zotti, Roberto Tagliaferri, Giuseppe Longo, Harri Teräsranta, Angelo Ciaramella, Merja Tornikoski, Anne Lähteenmäki, Leopoldo Milano, A., Ciaramella, C., Bongardo, H. D., Aller, M. F., Aller, G., DE ZOTTI, A., Lahteenmaki, Longo, Giuseppe, Milano, Leopoldo, R., Tagliaferri, H., Terasranta, M., Tornikoski, and AND S., Urpo
Subjects: Radiation mechanisms: non-thermal, FOS: Physical sciences, Flux, Astrophysics, 01 natural sciences, symbols.namesake, Radio continuum: general, Radio observatory, 0103 physical sciences, Planck, signal processing, Blazar, 010303 astronomy & astrophysics, Methods: statistical, Physics, 010308 nuclear & particles physics, Galaxies: BL Lacertae objects: general, Astrophysics (astro-ph), radiation mechanisms, non linear PCA, Astronomy and Astrophysics, Quasar, Galaxies: active, Light curve, CMB cold spot, Intensity (physics), Space and Planetary Science, symbols
Abstract: We have carried out a multifrequency analysis of the radio variability of blazars, exploiting the data obtained during the extensive monitoring programs carried out at the University of Michigan Radio Astronomy Observatory (UMRAO, at 4.8, 8, and 14.5 GHz) and at the Metsahovi Radio Observatory (22 and 37 GHz). Two different techniques detect, in the Metsahovi light curves, evidences of periodicity at both frequencies for 5 sources (0224+671, 0945+408, 1226+023, 2200+420, and 2251+158). For the last three sources consistent periods are found also at the three UMRAO frequencies and the Scargle (1982) method yields an extremely low false-alarm probability. On the other hand, the 22 and 37 GHz periodicities of 0224+671 and 0945+408 (which were less extensively monitored at Metsahovi and for which we get a significant false-alarm probability) are not confirmed by the UMRAO database, where some indications of ill-defined periods about a factor of two longer are retrieved. We have also investigated the variability index, the structure function, and the distribution of intensity variations of the most extensively monitored sources. We find a statistically significant difference in the distribution of the variability index for BL Lac objects compared to flat-spectrum radio quasars (FSRQs), in the sense that the former objects are more variable. For both populations the variability index steadily increases with increasing frequency. The distribution of intensity variations also broadens with increasing frequency, and approaches a log-normal shape at the highest frequencies. We find that variability enhances by 20-30% the high frequency counts of extragalactic radio-sources at bright flux densities, such as those of the WMAP and Planck surveys., Comment: A&A accepted. 12 pages, 16 figures
Published: 2004

23. VLBA observations of a rare multiple quasar imaging event caused by refraction in the interstellar medium

Author: Talvikki Hovatta, Anthony C. S. Readhead, Alexander B. Pushkarev, Matthew L. Lister, Eduardo Ros, J. A. Zensus, Margo F. Aller, H. D. Aller, Yuri Y. Kovalev, Walter Max-Moerbeck, Tuomas Savolainen, and Joseph L. Richards
Subjects: Astrofísica, Proper motion, Active galactic nucleus, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Angular diameter, 0103 physical sciences, Very-long-baseline interferometry, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Line (formation), Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Scattering, Astronomy and Astrophysics, Quasar, Interstellar medium, Space and Planetary Science, Astronomia, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We report on the first detection of the theoretically-predicted rare phenomenon of multiple parsec-scale imaging of an active galactic nucleus induced by refractive effects due to localized foreground electron density enhancements, e.g., in an AU-scale plasma lens(es) in the ionized component of the Galactic interstellar medium. We detected multiple imaging in the low galactic latitude (b=-2 deg) quasar 2023+335 from the 15.4 GHz MOJAVE observations when the source was undergoing an ESE. While the parsec-scale jet of the source normally extends along PA -20 deg, in the 28 May 2009 and 23 July 2009 images a highly significant multi-component pattern of secondary images is stretched out nearly along the constant galactic latitude line with a local PA 40 deg, indicating that the direction of relative motion of the plasma lens is close to orbital. Weaker but still detectable imaging patterns at similar position angles are sporadically manifest at several other epochs. Modeling the ESE that occurred in early 2009 and lasted ~0.14 yr, we determined that the foreground screen has a double-lens structure, with proper motion (~6.8 mas/yr), and angular size (~0.27 mas). We also found that the angular separation between the two brightest sub-images roughly follows a wavelength-squared dependence expected from plasma scattering. Furthermore, by analyzing archival non-simultaneous VLBA observations covering a wide frequency range from 1.4 to 86 GHz, we found that the scattered angular size of the VLBI core follows a $\nu^{-1.89}$ dependence, implying the presence of a turbulent, refractive dominated scattering screen that has a confined structure or is truncated transverse to the line of sight toward 2023+335., Comment: 13 pages, 7 figures, accepted for publication in A&A on 22 May, 2013
Published: 2013

24. III Zw 2: Evolution of a Radio Galaxy in a Nutshell

Author: Geoffrey C. Bower, Harri Teräsranta, Heino Falcke, Margo F. Aller, Thomas P. Krichbaum, H. D. Aller, and Andreas Brunthaler
Subjects: Physics, Active galactic nucleus, Superluminal motion, Space and Planetary Science, Radio galaxy, Milky Way, Molecular cloud, Astronomy, Astronomy and Astrophysics, Quasar, Astrophysics, Light curve, Galaxy
Abstract: III Zw 2 shows dramatic radio outbursts roughly every five years. Here we present the light curves and VLBA observations of the latest flare with an excellent time sampling. We have detected superluminal motion with a lower limit for the apparent expansion speed of 1.25±0.09 c at 43 GHz. Spectral and spatial evolution are closely linked and the evolution of III Zw 2 in a turnover frequency vs. linear size diagram is similar to the correlation for GPS and CSS sources. Before and after this rapid expansion we observe a period of virtually no expansion. However, at 15 GHz III Zw 2 shows a constant slow expansion (∼0.6 c). The difference is qualitatively explained by optical depth effects in an ‘inflating-balloon model’, describing the evolution of radio lobes on an ultra-compact scale. The stop-and-go behaviour could be explained by a jet interacting with a molecular cloud or the molecular torus.
Published: 2003
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25. MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VIII. Faraday rotation in parsec-scale AGN jets

Author: Talvikki Hovatta, Daniel C. Homan, Tuomas Savolainen, Alexander B. Pushkarev, Matthew L. Lister, H. D. Aller, Yuri Y. Kovalev, and Margo F. Aller
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Polarization (waves), Galaxy, law.invention, Magnetic field, symbols.namesake, Space and Planetary Science, law, Faraday effect, symbols, Faraday cage, Astrophysics - High Energy Astrophysical Phenomena, Very Long Baseline Array, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We report observations of Faraday rotation measures (RMs) for a sample of 191 extragalactic radio jets observed within the MOJAVE program. Multifrequency VLBA observations were carried out over twelve epochs in 2006 at four frequencies between 8 and 15 GHz. We detect parsec-scale Faraday RMs in 149 sources and find the quasars to have larger RMs on average than BL Lac objects. The median core RMs are significantly higher than in the jet components. This is especially true for quasars where we detect a significant negative correlation between the magnitude of the RM and the de-projected distance from the core. We perform detailed simulations of the observational errors of total intensity, polarization and Faraday rotation, and concentrate on the errors of transverse Faraday RM gradients in unresolved jets. Our simulations show that the finite image restoring beam size has a significant effect on the observed RM gradients, and spurious gradients can occur due to noise in the data if the jet is less than two beams wide in polarization. We detect significant transverse RM gradients in four sources (0923+392, 1226+023, 2230+114 and 2251+158). In 1226+023 the RM is for the first time seen to change sign from positive to negative over the transverse cuts, which supports the presence of a helical magnetic field in the jet. In this source we also detect variations in the jet RM over a time scale of three months, which are difficult to explain with external Faraday screens and suggest internal Faraday rotation. By comparing fractional polarization changes in jet components between the four frequency bands to depolarization models we find that an external purely random Faraday screen viewed through only a few lines of sight can explain most of our polarization observations but in some sources, such as 1226+023 and 2251+158, internal Faraday rotation is needed., Revised version wherein Figure 8 is corrected to include both of the epochs listed in the caption
Published: 2012

26. The broadband emission properties of AGN jets

Author: Matthias Kadler, Eduardo Ros, Margo F. Aller, Joern Wilms, Emmanouil Angelakis, Lars Fuhrmann, C. S. Chang, M. Boeck, H. D. Aller, and I. Nestoras
Subjects: Physics, Jet (fluid), Cosmology and Nongalactic Astrophysics (astro-ph.CO), Photon, Astrophysics::High Energy Astrophysical Phenomena, Hadron, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysical jet, Broadband, Very-long-baseline interferometry, Spectral energy distribution, Blazar, Astrophysics::Galaxy Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The origin of the high-energy emission of blazars is still a matter of debate. To investigate the emission mechanism of extragalactic outflows and to pin down the location of the emission, we have constructed a broadband spectral energy distribution (SED) database covering from the radio to the gamma-ray band for the complete MOJAVE sample, which consists of 135 relativistically beamed AGN with well-studied parsec-scale jets. Typically, the broadband SEDs of blazars shows a double-humped profile. It is believed that the lower-energy hump is due to synchrotron emission from the radio jet, and the higher-energy hump is generated by i) inverse-Compton upscattered seed photons (leptonic), ii) proton-induced shower (hadronic). Combining the results of high-resolution VLBI observations and the gamma-ray properties of the MOJAVE sources, we attempt to reveal the origin of the high-energy emission in relativistic jets, and search for correlations between VLBI and high-energy properties., Comment: 4 pages, 1 figure, 10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radio arrays, September 20-24, 2010, Manchester UK
Published: 2011
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27. Faraday rotation in the MOJAVE blazars: 3C 273 a case study

Author: Talvikki Hovatta, Daniel C. Homan, Margo F. Aller, Matthew L. Lister, Alexander B. Pushkarev, Tuomas Savolainen, H. D. Aller, and Yuri Y. Kovalev
Subjects: History, Active galactic nucleus, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 010501 environmental sciences, Rotation, 01 natural sciences, Education, symbols.namesake, 0103 physical sciences, Faraday effect, Blazar, 010303 astronomy & astrophysics, Very Long Baseline Array, 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Jet (fluid), Computer Science Applications, Magnetic field, Transverse plane, symbols, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio polarimetric observations of Active Galactic Nuclei can reveal the magnetic field structure in the parsec-scale jets of these sources. We have observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with the Very Long Baseline Array to study Faraday rotation in a large sample of jets. Our observations re-confirm the transverse rotation measure gradient in 3C 273. For the first time the gradient is seen to cross zero which is further indication for a helical magnetic field and spine-sheath structure in the jet. We believe the difference to previous epochs is due to a different part of the jet being illuminated in our observations., Comment: 6 pages, 3 figures. To appear in the proceedings of "Beamed and Unbeamed Gamma-rays from Galaxies", held in Muonio, Finland, April 11-15, 2011. Journal of Physics: Conference Series
Published: 2011
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28. The long-lasting activity of 3C 454.3: GASP-WEBT and satellite observations in 2008-2010

Author: C. M. Raiteri, M. Villata, M. F. Aller, M. A. Gurwell, O. M. Kurtanidze, A. Lähteenmäki, V. M. Larionov, P. Romano, S. Vercellone, I. Agudo, H. D. Aller, A. A. Arkharov, U. Bach, E. Benítez, A. Berdyugin, D. A. Blinov, E. V. Borisova, M. Böttcher, O. J. A. Bravo Calle, C. S. Buemi, P. Calcidese, D. Carosati, R. Casas, W.-P. Chen, N. V. Efimova, J. L. Gómez, C. Gusbar, K. Hawkins, J. Heidt, D. Hiriart, H. Y. Hsiao, B. Jordan, S. G. Jorstad, M. Joshi, G. N. Kimeridze, E. Koptelova, T. S. Konstantinova, E. N. Kopatskaya, S. O. Kurtanidze, E. G. Larionova, L. V. Larionova, P. Leto, Y. Li, R. Ligustri, E. Lindfors, M. Lister, A. P. Marscher, S. N. Molina, D. A. Morozova, E. Nieppola, M. G. Nikolashvili, K. Nilsson, N. Palma, M. Pasanen, R. Reinthal, V. Roberts, J. A. Ros, P. Roustazadeh, A. C. Sadun, T. Sakamoto, R. D. Schwartz, L. A. Sigua, A. Sillanpää, L. O. Takalo, J. Tammi, B. Taylor, M. Tornikoski, C. Trigilio, I. S. Troitsky, G. Umana, A. Volvach, T. A. Yuldasheva, Anne Lähteenmäki Group, Aalto-yliopisto, and Aalto University
Subjects: Photon, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, education, jets [galaxies], quasars: individual: 3C 454.3 [galaxies], Synchrotron radiation, Flux, FOS: Physical sciences, Astrophysics, 01 natural sciences, law.invention, law, 0103 physical sciences, 010303 astronomy & astrophysics, Physics, 010308 nuclear & particles physics, quasars: general [galaxies], Astronomy and Astrophysics, Light curve, Synchrotron, Wavelength, Amplitude, 13. Climate action, Space and Planetary Science, active [galaxies], Fermi Gamma-ray Space Telescope, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present multiwavelength observations of 3C 454.3 from April 2008 to March 2010. The radio to optical data are mostly from the GASP-WEBT, UV and X-ray data from Swift, and gamma-ray data from the AGILE and Fermi satellites. We improved the calibration of optical-UV data from the UVOT and OM instruments and estimated the Lyalpha flux to disentangle the contributions from different components in this spectral region. The observations reveal prominent variability above 8 GHz. In the optical-UV band, the variability amplitude decreases with increasing frequency due to a steadier radiation from both a broad line region and an accretion disc. The optical flux reaches nearly the same levels in the 2008-2009 and 2009-2010 observing seasons; the mm one shows similar behaviour, whereas the gamma and X-ray flux levels rise in the second period. Two prominent gamma-ray flares in mid 2008 and late 2009 show a double-peaked structure, with a variable gamma/optical flux ratio. The X-ray flux variations seem to follow the gamma-ray and optical ones by about 0.5 and 1 d, respectively. We interpret the multifrequency behaviour in terms of an inhomogeneous curved jet, where synchrotron radiation of increasing wavelength is produced in progressively outer and wider jet regions, which can change their orientation in time. In particular, we assume that the long-term variability is due to this geometrical effect. By combining the optical and mm light curves to fit the gamma and X-ray ones, we find that the gamma (X-ray) emission may be explained by inverse-Comptonisation of synchrotron optical (IR) photons by their parent relativistic electrons (SSC process). A slight, variable misalignment between the synchrotron and Comptonisation zones would explain the increased gamma and X-ray flux levels in 2009-2010, as well as the change in the gamma/optical flux ratio during the outbursts peaks., 17 pages, 9 figures, accepted for publication in A&A
Published: 2011

29. The catalog of periods of the variability of blazars 3C120, 3C273, 3C279, 3C345 and 3C454.3 at centimeter and millimeter wavelengths

Author: M. I. Ryabov, L. N. Volvach, M. F. Aller, A. E. Volvach, A. I. Suharev, and H. D. Aller
Subjects: Physics, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Flux, Astronomy, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Light curve, Radio telescope, Observatory, Millimeter, Blazar, Radio astronomy
Abstract: Variations in the radio flux of 3C120, 3C273, 3C279, 3C345, 3C 454.3 are analyzed using long‐term monitoring data at five frequencies from 4.8 to 36.8 GHz obtained at the University of Michigan Radio Astronomy Observatory and the Crimean Astrophysical Observatory. A spectral analysis of the light curves at the various frequencies reveals the presence of periodic components. Using method of model calculations for each of the found period tested its ability to reproduce the observed flux variability at different frequencies. On the basis of the model calculations presented the catalog of the most reliable periods of flux variable of radio sources.
Published: 2010
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30. Multiwavelength observations of markarian 421 in 2005-2006

Author: D. Horan, V. A. Acciari, S. M. Bradbury, J. H. Buckley, V. Bugaev, K. L. Byrum, A. Cannon, O. Celik, A. Cesarini, Y. C. K. Chow, L. Ciupik, P. Cogan, A. D. Falcone, S. J. Fegan, J. P. Finley, P. Fortin, L. F. Fortson, D. Gall, G. H. Gillanders, J. Grube, G. Gyuk, D. Hanna, E. Hays, M. Kertzman, J. Kildea, A. Konopelko, H. Krawczynski, F. Krennrich, M. J. Lang, K. Lee, P. Moriarty, T. Nagai, J. Niemiec, R. A. Ong, J. S. Perkins, M. Pohl, J. Quinn, P. T. Reynolds, H. J. Rose, G. H. Sembroski, A. W. Smith, D. Steele, S. P. Swordy, J. A. Toner, V. V. Vassiliev, S. P. Wakely, T. C. Weekes, R. J. White, D. A. Williams, M. D. Wood, B. Zitzer, H. D. Aller, M. F. Aller, M. Baker, D. Barnaby, M. T. Carini, P. Charlot, J. P. Dumm, N. E. Fields, T. Hovatta, B. Jordan, Y. A. Kovalev, Y. Y. Kovalev, H. A. Krimm, O. M. Kurtanidze, A. Lähteenmäki, J. F. Le Campion, J. Maune, T. Montaruli, A. C. Sadun, S. Smith, M. Tornikoski, M. Turunen, and R. Walters
Subjects: spectral slope variability, bl-lacertae objects, FOS: Physical sciences, bl lacertae objects: individual (markarian 421), proton blazar, tev blazar markarian-421, Astrophysics, timing explorer, Radio spectrum, law.invention, Telescope, Observatory, law, Blazar, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Northern Hemisphere, Astronomy and Astrophysics, gamma-ray emission, lac objects, Wavelength, x-ray, Space and Planetary Science, correlated variability, active galactic nuclei, Spectral energy distribution, Astrophysics - High Energy Astrophysical Phenomena, gamma rays: observations, x-rays: individual (markarian 421)
Abstract: Since September 2005, the Whipple 10m Gamma-ray Telescope has been operated primarily as a blazar monitor. The five Northern Hemisphere blazars that have already been detected at the Whipple Observatory, Markarian 421, H1426+428, Markarian 501, 1ES 1959+650 and 1ES 2344+514, are monitored routinely each night that they are visible. We report on the Markarian 421 observations taken from November 2005 to June 2006 in the gamma-ray, X-ray, optical and radio bands. During this time, Markarian 421 was found to be variable at all wavelengths probed. Both the variability and the correlations among different energy regimes are studied in detail here. A tentative correlation, with large spread, was measured between the X-ray and gamma-ray bands, while no clear correlation was evident among the other energy bands. In addition to this, the well-sampled spectral energy distribution of Markarian 421 (1101+384) is presented for three different activity levels. The observations of the other blazar targets will be reported separately., Comment: 58 pages, 22 Figures. Accepted for publication in ApJ
Published: 2009

31. Spectral Analysis of the Accretion Flow in NGC 1052 with Suzaku

Author: S. Kaufmann, Matthias Kadler, Jack Tueller, Jürgen Kerp, Margo F. Aller, Jimmy A. Irwin, Alan P. Marscher, Kimberly A. Weaver, Laura Brenneman, Eduardo Ros, Anton Zensus, H. D. Aller, and Yuri Y. Kovalev
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Plasma, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Accretion (astrophysics), Galaxy, Gravitation, Rotating black hole, Space and Planetary Science, Spectral analysis, Astrophysics - High Energy Astrophysical Phenomena, Equivalent width, Astrophysics::Galaxy Astrophysics
Abstract: We present an analysis of the 101 ks, 2007 Suzaku spectrum of the LINER galaxy NGC 1052. The 0.5-10 keV continuum is well-modeled by a power-law modified by Galactic and intrinsic absorption, and it exhibits a soft, thermal emission component below 1 keV. Both a narrow core and a broader component of Fe K emission centered at 6.4 keV are robustly detected. While the narrow line is consistent with an origin in material distant from the black hole, the broad line is best fit empirically by a model that describes fluorescent emission from the inner accretion disk around a rapidly rotating black hole. We find no evidence in this observation for Comptonized reflection of the hard X-ray source by the disk above 10 keV, however, which casts doubt on the hypothesis that the broad iron line originates in the inner regions of a standard accretion disk. We explore other possible scenarios for producing this spectral feature and conclude that the high equivalent width (EW ~ 185 keV) and full-width-half-maximum velocity of the broad iron line (v ~ 0.37c) necessitate an origin within d ~ 8 gravitational radii of the hard X-ray source. Based on the confirmed presence of a strong radio jet in this galaxy nucleus, the broad iron line may be produced in dense plasma near the base of the jet, implying that emission mechanisms in the centralmost portions of active galactic nuclei are more complex than previously thought., 33 pages, 8 figures, accepted for publication in ApJ
Published: 2009

32. Fermi Discovery of Gamma-Ray Emission from NGC 1275

Author: A. A. Abdo, M. Ackermann, M. Ajello, K. Asano, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, B. M. Baughman, K. Bechtol, R. Bellazzini, R. D. Blandford, E. D. Bloom, E. Bonamente, A. W. Borgland, J. Bregeon, A. Brez, M. Brigida, P. Bruel, T. H. Burnett, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, J. M. Casandjian, E. Cavazzuti, C. Cecchi, A. Celotti, A. Chekhtman, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, S. Colafrancesco, L. R. Cominsky, J. Conrad, L. Costamante, C. D. Dermer, A. de Angelis, F. de Palma, S. W. Digel, D. Donato, E. do Couto e Silva, P. S. Drell, R. Dubois, D. Dumora, C. Farnier, C. Favuzzi, J. Finke, W. B. Focke, M. Frailis, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, M. Georganopoulos, S. Germani, B. Giebels, N. Giglietto, F. Giordano, T. Glanzman, I. A. Grenier, M.-H. Grondin, J. E. Grove, L. Guillemot, S. Guiriec, Y. Hanabata, A. K. Harding, R. C. Hartman, M. Hayashida, E. Hays, R. E. Hughes, G. Jóhannesson, A. S. Johnson, R. P. Johnson, W. N. Johnson, M. Kadler, T. Kamae, Y. Kanai, H. Katagiri, J. Kataoka, N. Kawai, M. Kerr, J. Knödlseder, F. Kuehn, M. Kuss, L. Latronico, M. Lemoine-Goumard, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, A. Makeev, M. N. Mazziotta, J. E. McEnery, C. Meurer, P. F. Michelson, W. Mitthumsiri, T. Mizuno, A. A. Moiseev, C. Monte, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, T. Nakamori, P. L. Nolan, J. P. Norris, E. Nuss, T. Ohsugi, N. Omodei, E. Orlando, J. F. Ormes, D. Paneque, J. H. Panetta, D. Parent, M. Pepe, M. Pesce-Rollins, F. Piron, T. A. Porter, S. Rainò, M. Razzano, A. Reimer, O. Reimer, T. Reposeur, S. Ritz, A. Y. Rodriguez, R. W. Romani, F. Ryde, H. F.-W. Sadrozinski, R. Sambruna, D. Sanchez, A. Sander, R. Sato, P. M. Saz Parkinson, C. Sgrò, D. A. Smith, P. D. Smith, G. Spandre, P. Spinelli, J.-L. Starck, M. S. Strickman, A. W. Strong, D. J. Suson, H. Tajima, H. Takahashi, T. Takahashi, T. Tanaka, G. B. Taylor, J. G. Thayer, D. J. Thompson, D. F. Torres, G. Tosti, Y. Uchiyama, T. L. Usher, N. Vilchez, V. Vitale, A. P. Waite, K. S. Wood, T. Ylinen, M. Ziegler, H. D. Aller, M. F. Aller, K. I. Kellermann, Y. Y. Kovalev, Yu. A. Kovalev, M. L. Lister, A. B. Pushkarev, Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Leprince-Ringuet (LLR), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique Théorique et Astroparticules (LPTA), Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre d'étude spatiale des rayonnements (CESR), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Fermi-LAT, Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), Université Sciences et Technologies - Bordeaux 1-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Abdo, A. A., Ackermann, M., Ajello, M., Asano, K., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Baughman, B. M., Bechtol, K., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Borgland, A. W., Bregeon, J., Brez, A., Brigida, M., Bruel, P., Burnett, T. H., Caliandro, G. A., Cameron, R. A., Caraveo, A., Casandjian, J. M., Cavazzuti, E., Cecchi, C., Celotti, A., Chekhtman, A., Cheung, C. C., Chiang, J., Ciprini, S., Claus, R., Cohen Tanugi, J., Colafrancesco, S., Cominsky, L. R., Conrad, J., Costamante, L., Dermer, C. D., Angelis, A. d., Palma, F. d., Digel, S. W., Donato, D., Silva, E. D. E., Drell, P. S., Dubois, R., Dumora, D., Farnier, C., Favuzzi, C., Finke, J., Focke, W. B., Frailis, M., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Georganopoulos, M., Germani, S., Giebels, B., Giglietto, N., Giordano, F., Glanzman, T., Grenier, I. A., Grondin, M. H., Grove, J. E., Guillemot, L., Guiriec, S., Hanabata, Y., Harding, A. K., Hartman, R. C., Hayashida, M., Hays, E., Hughes, R. E., Johannesson, G., Johnson, A. S., Johnson, R. P., Johnson, W. N., Kadler, M., Kamae, T., Kanai, Y., Katagiri, H., Kataoka, J., Kawai, N., Kerr, M., Knodlseder, J., Kuehn, F., Kuss, M., Latronico, L., Lemoine Goumard, M., Longo, Francesco, Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Madejski, G. M., Makeev, A., Mazziotta, M. N., Mcenery, J. E., Meurer, C., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A., Monte, C., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nakamori, T., Nolan, L., Norris, J. P., Nuss, E., Ohsugi, T., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Panetta, J. H., Parent, D., Pepe, M., Pesce Rollins, M., Piron, F., Porter, T. A., Raino, S., Razzano, M., Reimer, A., Reimer, O., Reposeur, T., Ritz, S., Rodriguez, A. Y., Romani, R. W., Ryde, F., Sadrozinski, H. F. W., Sambruna, R., Sanchez, D., Sander, A., Sato, R., Parkinson, P. M. S., Sgro, C., Smith, D. A., Smith, P. D., Spandre, G., Spinelli, P., Starck, J. L., Strickman, M. S., Strong, A. W., Suson, D. J., Tajima, H., Takahashi, H., Takahashi, T., Tanaka, T., Taylor, G. B., Thayer, J. G., Thompson, D. J., Torres, D. F., Tosti, G., Uchiyama, Y., Usher, T. L., Vilchez, N., Vitale, V., Waite, A. P., Wood, K. S., Ylinen, T., Ziegler, M., Aller, H. D., Aller, M. F., Kellermann, K. I., Kovalev, Y. Y., Kovalev, Y. A., Lister, M. L., and Pushkarev, A. B.
Subjects: [PHYS.ASTR.HE]Physics [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE], Cosmology and Nongalactic Astrophysics (astro-ph.CO), Radiation mechanisms: non-thermal, Point source, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Flux, Fermi satellite, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Gamma rays: observations, 01 natural sciences, High Energy Gamma-ray Astronomy, law.invention, Telescope, Galaxies: individual (NGC 1275), Settore FIS/05 - Astronomia e Astrofisica, law, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Galaxies: active, Galaxies: jets, 010308 nuclear & particles physics, Gamma ray, Center (category theory), galaxies: active, galaxies: individual: NGC 1275, galaxies: jets, gamma rays: observations, radiation mechanisms: non-thermal, Astronomy and Astrophysics, Galaxies, Galaxy, Space and Planetary Science, Elliptical galaxy, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Fermi Gamma-ray Space Telescope
Abstract: 著者人数：170名, Accepted: 2009-04-20, 資料番号: SA1000972000
Published: 2009
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33. Long-term variability of radio-bright BL Lacertae objects

Author: Merja Tornikoski, Margo F. Aller, E. Nieppola, Talvikki Hovatta, H. D. Aller, and Esko Valtaoja
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010504 meteorology & atmospheric sciences, Structure function, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Correlation function (astronomy), 01 natural sciences, Term (time), law.invention, Wavelength, symbols.namesake, Space and Planetary Science, law, 0103 physical sciences, symbols, Range (statistics), Adiabatic process, 010303 astronomy & astrophysics, Doppler effect, Astrophysics - Cosmology and Nongalactic Astrophysics, 0105 earth and related environmental sciences, Flare
Abstract: Radio-bright BL Lacertae objects (BLOs) are typically variable and exhibit prominent flaring. We use a sample of 24 BLOs to get a clear idea of their flaring behavior and to find possible commonalities in their variability patterns. Our goal was to compare the results given by computational time scales and the observed variability parameters determined directly from the flux curves. Also, we wanted to find out if the BLO flares adhere to the generalized shock model. We use long-term monitoring data from 4.8, 8, 14.5, 22, 37, 90 and 230 GHz. The structure function, discrete correlation function and Lomb-Scargle periodogram time scales, calculated in a previous study, are analyzed in more detail. We determine flare durations, rise and decay times, absolute and relative peak fluxes from the monitoring data. We find that BLOs demonstrate a wide range of variability behavior. BLOs include sources with fast and strong variability, such as OJ 287, PKS 1749+096 and BL Lac, but also sources with more rolling fluctuations like PKS 0735+178. The most extreme flares can last for up to 13 years or have peak fluxes of approximately 12 Jy in the observer's frame. When the Doppler boosting effect is taken into account, the peak flux of a flare does not depend on the duration of the flare. A rough analysis of the time lags and peak flux evolution indicates that BLO flares in the mm - cm wavelengths are high-peaking, i.e., are in the adiabatic stage. Thus, the results concur with the generalized shock model., Comment: Published in the Astronomical Journal
Published: 2009
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34. WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008. Unveiling different emission components

Author: C. M. Raiteri, M. Villata, A. Capetti, M. F. Aller, U. Bach, P. Calcidese, M. A. Gurwell, V. M. Larionov, J. Ohlert, K. Nilsson, A. Strigachev, I. Agudo, H. D. Aller, R. Bachev, E. Benítez, A. Berdyugin, M. Böttcher, C. S. Buemi, S. Buttiglione, D. Carosati, P. Charlot, W. P. Chen, D. Dultzin, E. Forné, L. Fuhrmann, J. L. Gómez, A. C. Gupta, J. Heidt, D. Hiriart, W.-S. Hsiao, M. Jelínek, S. G. Jorstad, G. N. Kimeridze, T. S. Konstantinova, E. N. Kopatskaya, A. Kostov, O. M. Kurtanidze, A. Lähteenmäki, L. Lanteri, L. V. Larionova, P. Leto, G. Latev, J.-F. Le Campion, C.-U. Lee, R. Ligustri, E. Lindfors, A. P. Marscher, B. Mihov, M. G. Nikolashvili, Y. Nikolov, E. Ovcharov, D. Principe, T. Pursimo, B. Ragozzine, R. M. Robb, J. A. Ros, A. C. Sadun, R. Sagar, E. Semkov, L. A. Sigua, R. L. Smart, M. Sorcia, L. O. Takalo, M. Tornikoski, C. Trigilio, K. Uckert, G. Umana, A. Valcheva, A. Volvach, INAF - Osservatorio Astrofisico di Torino (OATo), Istituto Nazionale di Astrofisica (INAF), Instituto de Neurociencias de Alicante, Universidad Miguel Hernández [Elche] (UMH), Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), and Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Brightness, [PHYS.ASTR.HE]Physics [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE], Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Power law, Spectral line, Luminosity, law.invention, Telescope, law, 0103 physical sciences, Blazar, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Line-of-sight, 010308 nuclear & particles physics, Molecular cloud, [SDU.ASTR.HE]Sciences of the Universe [physics]/Astrophysics [astro-ph]/High Energy Astrophysical Phenomena [astro-ph.HE], Astronomy and Astrophysics, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: In 2007-2008 we carried out a new multiwavelength campaign of the Whole Earth Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the XMM-Newton satellite, to study its emission properties. The source was monitored in the optical-to-radio bands by 37 telescopes. The brightness level was relatively low. Some episodes of very fast variability were detected in the optical bands. The X-ray spectra are well fitted by a power law with photon index of about 2 and photoelectric absorption exceeding the Galactic value. However, when taking into account the presence of a molecular cloud on the line of sight, the data are best fitted by a double power law, implying a concave X-ray spectrum. The spectral energy distributions (SEDs) built with simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations suggest that the peak of the synchrotron emission lies in the near-IR band, and show a prominent UV excess, besides a slight soft-X-ray excess. A comparison with the SEDs corresponding to previous observations with X-ray satellites shows that the X-ray spectrum is extremely variable. We ascribe the UV excess to thermal emission from the accretion disc, and the other broad-band spectral features to the presence of two synchrotron components, with their related SSC emission. We fit the thermal emission with a black body law and the non-thermal components by means of a helical jet model. The fit indicates a disc temperature greater than 20000 K and a luminosity greater than 6 x 10^44 erg/s., 11 pages, 7 figures, accepted for publication in A&A
Published: 2009

35. The GASP-WEBT monitoring of 3C 454.3 during the 2008 optical-to-radio and gamma-ray outburst

Author: M. Villata, C. M. Raiteri, M. A. Gurwell, V. M. Larionov, O. M. Kurtanidze, M. F. Aller, A. Lähteenmäki, W. P. Chen, K. Nilsson, I. Agudo, H. D. Aller, A. A. Arkharov, U. Bach, R. Bachev, P. Beltrame, E. Benítez, C. S. Buemi, M. Böttcher, P. Calcidese, D. Capezzali, D. Carosati, D. Da Rio, A. Di Paola, M. Dolci, D. Dultzin, E. Forné, J. L. Gómez, V. A. Hagen-Thorn, A. Halkola, J. Heidt, D. Hiriart, T. Hovatta, H.-Y. Hsiao, S. G. Jorstad, G. N. Kimeridze, T. S. Konstantinova, E. N. Kopatskaya, E. Koptelova, P. Leto, R. Ligustri, E. Lindfors, J. M. Lopez, A. P. Marscher, M. Mommert, R. Mujica, M. G. Nikolashvili, N. Palma, M. Pasanen, M. Roca-Sogorb, J. A. Ros, P. Roustazadeh, A. C. Sadun, J. Saino, L. A. Sigua, M. Sorcia, L. O. Takalo, M. Tornikoski, C. Trigilio, R. Turchetti, and G. Umana
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Brightness, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, Gamma ray, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, law.invention, Telescope, Space and Planetary Science, law, Radio frequency, Blazar, Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Since 2001, the radio quasar 3C 454.3 has undergone a period of high optical activity, culminating in the brightest optical state ever observed, during the 2004-2005 outburst. The Whole Earth Blazar Telescope (WEBT) consortium has carried out several multifrequency campaigns to follow the source behaviour. The GLAST-AGILE Support Program (GASP) was born from the WEBT to provide long-term continuous optical-to-radio monitoring of a sample of gamma-loud blazars, during the operation of the AGILE and GLAST (now known as Fermi GST) gamma-ray satellites. The main aim is to shed light on the mechanisms producing the high-energy radiation, through correlation analysis with the low-energy emission. Thus, since 2008 the monitoring task on 3C 454.3 passed from the WEBT to the GASP, while both AGILE and Fermi detected strong gamma-ray emission from the source. We present the main results obtained by the GASP at optical, mm, and radio frequencies in the 2008-2009 season, and compare them with the WEBT results from previous years. An optical outburst was observed to peak in mid July 2008, when Fermi detected the brightest gamma-ray levels. A contemporaneous mm outburst maintained its brightness for a longer time, until the cm emission also reached the maximum levels. The behaviour compared in the three bands suggests that the variable relative brightness of the different-frequency outbursts may be due to the changing orientation of a curved inhomogeneous jet. The optical light curve is very well sampled during the entire season, which is also well covered by the various AGILE and Fermi observing periods. The relevant cross-correlation studies will be very important in constraining high-energy emission models., Comment: 5 pages, 5 figures, to be published in A&A (Letters)
Published: 2009
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36. Full Polarization Spectra of 3C 279

Author: Daniel C. Homan, H. D. Aller, Margo F. Aller, Matthew L. Lister, and John F. C. Wardle
Subjects: Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, Linear polarization, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Electron, Astrophysics, Polarization (waves), 01 natural sciences, Magnetic flux, Relativistic particle, Computational physics, Magnetic field, symbols.namesake, Space and Planetary Science, 0103 physical sciences, Faraday effect, symbols, 010303 astronomy & astrophysics, Circular polarization, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We report the results of parsec-scale, multi-frequency VLBA observations of the core region of 3C 279 in Stokes I, linear polarization, and circular polarization. These full polarization spectra are modeled by radiative transfer simulations to constrain the magnetic field and particle properties of the parsec-scale jet in 3C 279. The polarization properties of the core region, including the amount of linear polarization, the amount and sign of Faraday rotation, and the amount and sign of circular polarization can be explained by a consistent physical picture. The base of the jet is modeled as an inhomogeneous Blandford-Konigl style conical jet dominated by a vector-ordered poloidal magnetic field along the jet axis, and we estimate its net magnetic flux. This poloidal field is responsible for the linear and circular polarization from this inhomogeneous component. Farther down the jet the magnetic field in two homogeneous features is dominated by local shocks and a smaller fraction of vector-ordered poloidal field remains along the jet axis. In this picture, we find the jet to be kinetically dominated by protons with the radiating particles being dominated by electrons at an approximate fraction of >~ 75%. Based on the amounts of Faraday conversion deduced for the homogeneous components, we find a plausible range for the lower cutoff in the relativistic particle energy spectrum to be 5, Comment: 21 pages, 12 figures, accepted to appear in The Astrophysical Journal
Published: 2009
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37. The correlated optical and radio variability of BL Lacertae. WEBT data analysis 1994-2005

Author: M. Villata, C. M. Raiteri, V. M. Larionov, M. G. Nikolashvili, M. F. Aller, U. Bach, D. Carosati, F. Hroch, M. A. Ibrahimov, S. G. Jorstad, Y. Y. Kovalev, A. Lähteenmäki, K. Nilsson, H. Teräsranta, G. Tosti, H. D. Aller, A. A. Arkharov, A. Berdyugin, P. Boltwood, C. S. Buemi, R. Casas, P. Charlot, J. M. Coloma, A. Di Paola, G. Di Rico, G. N. Kimeridze, T. S. Konstantinova, E. N. Kopatskaya, Yu. A. Kovalev, O. M. Kurtanidze, L. Lanteri, E. G. Larionova, L. V. Larionova, J.-F. Le Campion, P. Leto, E. Lindfors, A. P. Marscher, K. Marshall, J. P. McFarland, I. M. McHardy, H. R. Miller, G. Nucciarelli, M. P. Osterman, M. Pasanen, T. Pursimo, J. A. Ros, A. C. Sadun, L. A. Sigua, L. Sixtova, L. O. Takalo, M. Tornikoski, C. Trigilio, G. Umana, G. Z. Xie, X. Zhang, S. B. Zhou, INAF - Osservatorio Astrofisico di Torino (OATo), Istituto Nazionale di Astrofisica (INAF), Instituto de Neurociencias de Alicante, Universidad Miguel Hernández [Elche] (UMH), Dipartimento di Fisica e Geologia [Perugia], Università degli Studi di Perugia = University of Perugia (UNIPG), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Departamento de Bioquímica y Biología Molecular, Universitat de València (UV), Abteilung Klinische Sozialmedizin, Berufs- und Umweltdermatologie, Universität Heidelberg [Heidelberg] = Heidelberg University, Institut des Sciences Chimiques de Rennes (ISCR), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Università degli Studi di Perugia (UNIPG), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Facultad de Farmacia, Universidad de Valencia, Valencia, Spain, Universität Heidelberg [Heidelberg], Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), and Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], galaxies: active, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], FOS: Physical sciences, Astrophysics, 01 natural sciences, law.invention, Telescope, law, 0103 physical sciences, BL+Lacertae<%2FASTROBJ>%22">galaxies: BL Lacertae objects: individual: BL Lacertae, Blazar, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, Physics, galaxies: BL Lacertae objects: individual: BL Lacertae, 010308 nuclear & particles physics, galaxies: BL Lacertae objects: general, galaxies: jets, galaxies: quasars: general, Radio flux, Astronomy and Astrophysics, Light curve, Space and Planetary Science, Correlation analysis, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Since 1997, BL Lacertae has undergone a phase of high optical activity, with the occurrence of several prominent outbursts. Starting from 1999, the Whole Earth Blazar Telescope (WEBT) consortium has organized various multifrequency campaigns on this blazar, collecting tens of thousands of data points. One of the main issues in the study of this huge dataset has been the search for correlations between the optical and radio flux variations, and for possible periodicities in the light curves. The analysis of the data assembled during the first four campaigns (comprising also archival data to cover the period 1968-2003) revealed a fair optical-radio correlation in 1994-2003, with a delay of the hard radio events of ~100 days. Moreover, various statistical methods suggested the existence of a radio periodicity of ~8 years. In 2004 the WEBT started a new campaign to extend the dataset to the most recent observing seasons, in order to possibly confirm and better understand the previous results. In this campaign we have collected and assembled about 11000 new optical observations from twenty telescopes, plus near-IR and radio data at various frequencies. Here, we perform a correlation analysis on the long-term R-band and radio light curves. In general, we confirm the ~100-day delay of the hard radio events with respect to the optical ones, even if longer (~200-300 days) time lags are also found in particular periods. The radio quasi-periodicity is confirmed too, but the "period" seems to progressively lengthen from 7.4 to 9.3 years in the last three cycles. The optical and radio behaviour in the last forty years suggests a scenario where geometric effects play a major role. In particular, the alternation of enhanced and suppressed optical activity (accompanied by hard and soft radio events, respectively) can, Comment: 6 pages, 4 figures
Published: 2009
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38. Long-term radio variability of AGN: flare characteristics

Author: Margo F. Aller, Talvikki Hovatta, E. Nieppola, Merja Tornikoski, H. D. Aller, and Esko Valtaoja
Subjects: Physics, Time delays, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Sampling (statistics), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Radio spectrum, Term (time), law.invention, Telescope, Radio observatory, Space and Planetary Science, law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Energy (signal processing), Astrophysics::Galaxy Astrophysics, Flare
Abstract: We have studied the flare characteristics of 55 AGN at 8 different frequency bands between 4.8 and 230 GHz. Our extensive database enables us to study the various observational properties of flares in these sources and compare our results with theoretical models. We visually extracted 159 individual flares from the flux density curves and calculated different parameters, such as the peak flux density and duration, in all the frequency bands. The selection of flares is based on the 22 and 37 GHz data from Mets\"ahovi Radio Observatory and 90 and 230 GHz data from the SEST telescope. Additional lower frequency 4.8, 8, and 14.5 GHz data are from the University of Michigan Radio Observatory. We also calculated variability indices and compared them with earlier studies. The observations seem to adhere well to the shock model, but there is still large scatter in the data. Especially the time delays between different frequency bands are difficult to study due to the incomplete sampling of the higher frequencies. The average duration of the flares is 2.5 years at 22 and 37 GHz, which shows that long-term monitoring is essential for understanding the typical behaviour in these sources. It also seems that the energy release in a flare is independent of the duration of the flare., Comment: 11 pages, 9 figures, 2 tables, accepted for publication in A&A
Published: 2008

39. Long term radio variability of AGN

Author: Harry J. Lehto, Margo F. Aller, Markku Lainela, Anne Lähteenmäki, Merja Tornikoski, E. Nieppola, Talvikki Hovatta, H. D. Aller, I. Torniainen, and Esko Valtaoja
Subjects: Physics, Radio observatory, biology, Elina, Observatory, Astrophysics (astro-ph), Library science, FOS: Physical sciences, Astrophysics, biology.organism_classification, Term (time)
Abstract: A large number of AGN have been monitored for nearly 30 years at 22, 37 and 87 GHz in Mets\"ahovi Radio Observatory. These data were combined with lower frequency 4.8, 8.0 and 14.5 GHz data from the University of Michigan Radio Astronomy Observatory, higher frequency data at 90 and 230 GHz from SEST, and supplementary higher frequency data from the literature to study the long-term variability of a large sample of AGN. Both the characteristics of individual flares from visual inspection and statistically-determined variability timescales as a function of frequency and optical class type were determined. Based on past behaviour, predictions of sources expected to exhibit large flares in 2008--2009 appropriate for study by GLAST and other instruments are made. The need for long-term data for properly understanding source behaviour is emphasised., Comment: 7 pages, 3 figures, "Workshop on Blazar Variability across the Electromagnetic Spectrum", 2008 April 22-25, Palaiseau, France
Published: 2008
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40. The multiwavelength variability of 3C 273

Author: E. I. Robson, Ian M. McHardy, R. Walter, Marc Türler, G. Burki, Merja Tornikoski, Margo F. Aller, Simona Soldi, Stéphane Paltani, Thierry J.-L. Courvoisier, Maria Chernyakova, Ruediger Staubert, Anne Lähteenmäki, and H. D. Aller
Subjects: Shock wave, Physics, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Synchrotron radiation, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Electron, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, 01 natural sciences, Synchrotron, law.invention, Amplitude, 13. Climate action, Space and Planetary Science, law, 0103 physical sciences, Millimeter, 010303 astronomy & astrophysics
Abstract: We present an update of 3C 273's database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the multiwavelength properties of this quasar,especially focussing on its variability behaviour. We study the amplitude of the variations and the maximum variability time scales across the broad-band spectrum and correlate the light curves in different bands, specifically with the X-rays, to search for possible connections between the emission at different energies. 3C 273 shows variability at all frequencies, with amplitudes and time scales strongly depending on the energy and being the signatures of the different emission mechanisms. The variability properties of the X-ray band imply the presence of either two separate components (possibly a Seyfert-like and a blazar-like) or at least two parameters with distinct timing properties to account for the X-ray emission below and above ~20 keV. The dominant hard X-ray emission is most probably not due to electrons accelerated by the shock waves in the jet as their variability does not correlate with the flaring millimeter emission, but seems to be associated to long-timescale variations in the optical. This optical component is consistent with being optically thin synchrotron radiation from the base of the jet and the hard X-rays would be produced through inverse Compton processes (SSC and/or EC) by the same electron population. We show evidence that this synchrotron component extends from the optical to the near-infrared domain, where it is blended by emission of heated dust that we find to be located within about 1 light-year from the ultraviolet source., Comment: 16 pages, 13 figures, 2 tables, accepted for publication in A&A
Published: 2008
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41. Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007

Author: M. Villata, C. M. Raiteri, V. M. Larionov, O. M. Kurtanidze, K. Nilsson, M. F. Aller, M. Tornikoski, A. Volvach, H. D. Aller, A. A. Arkharov, U. Bach, P. Beltrame, G. Bhatta, C. S. Buemi, M. Böttcher, P. Calcidese, D. Carosati, A. J. Castro-Tirado, D. Da Rio, A. Di Paola, M. Dolci, E. Forné, A. Frasca, V. A. Hagen-Thorn, J. Heidt, D. Hiriart, M. Jelínek, G. N. Kimeridze, T. S. Konstantinova, E. N. Kopatskaya, L. Lanteri, P. Leto, R. Ligustri, E. Lindfors, A. Lähteenmäki, E. Marilli, E. Nieppola, M. G. Nikolashvili, M. Pasanen, B. Ragozzine, J. A. Ros, L. A. Sigua, R. L. Smart, M. Sorcia, L. O. Takalo, M. Tavani, C. Trigilio, R. Turchetti, K. Uckert, G. Umana, S. Vercellone, and J. R. Webb
Subjects: Physics, Swift, business.industry, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Light curve, law.invention, Telescope, Space and Planetary Science, law, Monitoring data, Blazar, business, computer, computer.programming_language, Agile software development
Abstract: Since the CGRO operation in 1991-2000, one of the primary unresolved questions about the blazar gamma-ray emission has been its possible correlation with the low-energy (in particular optical) emission. To help answer this problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring data to be compared with the gamma-ray detections by the AGILE and GLAST satellites. This new WEBT project started in early September 2007, just before a strong gamma-ray detection of 0716+714 by AGILE. We present the GASP-WEBT optical and radio light curves of this blazar obtained in July-November 2007, about various AGILE pointings at the source. We construct NIR-to-UV spectral energy distributions (SEDs), by assembling GASP-WEBT data together with UV data from the Swift ToO observations of late October. We observe a contemporaneous optical-radio outburst, which is a rare and interesting phenomenon in blazars. The shape of the SEDs during the outburst appears peculiarly wavy because of an optical excess and a UV drop-and-rise. The optical light curve is well sampled during the AGILE pointings, showing prominent and sharp flares. A future cross-correlation analysis of the optical and AGILE data will shed light on the expected relationship between these flares and the gamma-ray events., 5 pages, 5 figures, to be published in A&A (Letters); revised to match the final version (changes in Fig. 5 and related text)
Published: 2008

42. The high activity of 3C 454.3 in autumn 2007. Monitoring by the WEBT during the AGILE detection

Author: C. M. Raiteri, M. Villata, W. P. Chen, W.-S. Hsiao, O. M. Kurtanidze, K. Nilsson, V. M. Larionov, M. A. Gurwell, I. Agudo, H. D. Aller, M. F. Aller, E. Angelakis, A. A. Arkharov, U. Bach, M. Böttcher, C. S. Buemi, P. Calcidese, P. Charlot, F. D'Ammando, I. Donnarumma, E. Forné, A. Frasca, L. Fuhrmann, J. L. Gómez, V. A. Hagen-Thorn, S. G. Jorstad, G. N. Kimeridze, T. P. Krichbaum, A. Lähteenmäki, L. Lanteri, G. Latev, J.-F. Le Campion, C.-U. Lee, P. Leto, H.-C. Lin, N. Marchili, E. Marilli, A. P. Marscher, R. Nesci, E. Nieppola, M. G. Nikolashvili, J. Ohlert, E. Ovcharov, D. Principe, T. Pursimo, B. Ragozzine, A. C. Sadun, L. A. Sigua, R. L. Smart, A. Strigachev, L. O. Takalo, M. Tavani, C. Thum, M. Tornikoski, C. Trigilio, K. Uckert, G. Umana, A. Valcheva, S. Vercellone, A. Volvach, H. Wiesemeyer, INAF - Osservatorio Astrofisico di Torino (OATo), Istituto Nazionale di Astrofisica (INAF), Laboratoire de Physico-Chimie de l'Atmosphère (LPCA), Centre National de la Recherche Scientifique (CNRS)-Université du Littoral Côte d'Opale, Laboratoire de chimie bactérienne (LCB), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS), Fujian Institute of Research on the Structure of Matter, National Engineering Research Center for Optoelectronic Crystalline Materials, Chinese Academy of Sciences, Insitute of Geology China Earthquake Administration Beijing 100029, China (X.X., G.C., W.C.) (INSITUTE OF GEOLOGY), Insitute of Geology, ECE Dept., University of Wisconsin-Madison, Harbin Institute of Technology (HIT), Department of Information Science and Media Studies [Bergen], University of Bergen (UIB), Institute of Geology, Chinese Academy of Sciences [Changchun Branch] (CAS), Linköping University (LIU), Department of Mechanical Engineering, National Chung-Hsing University, Research Center for Environmental Changes, Institute of Earthquake Prediction Research, Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université du Littoral Côte d'Opale (ULCO)-Centre National de la Recherche Scientifique (CNRS), Department of Information Science and Media Studies [Bergen] (UiB), University of Bergen (UiB), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Raiteri CM, Villata M, Chen WP, Hsiao WS, Kurtanidze OM, Nilsson K, Larionov VM, Gurwell MA, Agudo I, Aller HD, Aller MF, Angelakis E, Arkharov AA, Bach U, Bottcher M, Buemi CS, Calcidese P, Charlot P, DAmmando F, Donnarumma I, Forne E, Frasca A, Fuhrmann L, Gomez JL, Hagen-Thorn VA, Jorstad SG, Kimeridze GN, Krichbaum TP, Lahteenmaki A, Lanteri L, Latev G, Le Campion JF, Lee CU, Leto P, Lin HC, Marchili N, Marilli E, Marscher AP, Nesci R, Nieppola E, Nikolashvili MG, Ohlert J, Ovcharov E, Principe D, Pursimo T, Ragozzine B, Sadun AC, Sigua LA, Smart RL, Strigachev A, Takalo LO, Tavani M, Thum C, Tornikoski M, Trigilio C, Uckert K, Umana G, Valcheva A, Vercellone S, Volvach A, and Wiesemeyer H
Subjects: Brightness, Swift Gamma-Ray Burst Mission, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Extinction (astronomy), galaxies: active, FOS: Physical sciences, Flux, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, galaxies: active -- galaxies: quasars: general -- galaxies: quasars: individual: 3C 454.3, 01 natural sciences, law.invention, Telescope, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], law, 0103 physical sciences, galaxies: quasars: individual: 3C 454.3, Blazar, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics (astro-ph), Astronomy and Astrophysics, Light curve, galaxies: quasars: general, Space and Planetary Science, Satellite
Abstract: The quasar-type blazar 3C 454.3 underwent a phase of high activity in summer and autumn 2007, which was intensively monitored in the radio-to-optical bands by the Whole Earth Blazar Telescope (WEBT). The gamma-ray satellite AGILE detected this source first in late July, and then in November-December 2007. In this letter we present the multifrequency data collected by the WEBT and collaborators during the second AGILE observing period, complemented by a few contemporaneous data from UVOT onboard the Swift satellite. The aim is to trace in detail the behaviour of the synchrotron emission from the blazar jet, and to investigate the contribution from the thermal emission component. Optical data from about twenty telescopes have been homogeneously calibrated and carefully assembled to construct an R-band light curve containing about 1340 data points in 42 days. This extremely well-sampled optical light curve allows us to follow the dramatic flux variability of the source in detail. In addition, we show radio-to-UV spectral energy distributions (SEDs) at different epochs, which represent different brightness levels. In the considered period, the source varied by 2.6 mag in a couple of weeks in the R band. Many episodes of fast (i.e. intranight) variability were observed, most notably on December 12, when a flux increase of about 1.1 mag in 1.5 hours was detected, followed by a steep decrease of about 1.2 mag in 1 hour. The contribution by the thermal component is difficult to assess, due to the uncertainties in the Galactic, and possibly also intrinsic, extinction in the UV band. However, polynomial fitting of radio-to-UV SEDs reveals an increasing spectral bending going towards fainter states, suggesting a UV excess likely due to the thermal emission from the accretion disc., 5 pages, 4 figures, accepted for publication in Astronomy & Astrophysics Letters
Published: 2008
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43. WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst phase. Detection of the little and big blue bumps

Author: C. M. Raiteri, M. Villata, V. M. Larionov, T. Pursimo, M. A. Ibrahimov, K. Nilsson, M. F. Aller, O. M. Kurtanidze, L. Foschini, J. Ohlert, I. E. Papadakis, N. Sumitomo, A. Volvach, H. D. Aller, A. A. Arkharov, U. Bach, A. Berdyugin, M. Böttcher, C. S. Buemi, P. Calcidese, P. Charlot, A. J. Delgado Sánchez, A. Di Paola, A. A. Djupvik, M. Dolci, N. V. Efimova, J. H. Fan, E. Forné, C. A. Gomez, A. C. Gupta, V. A. Hagen-Thorn, L. Hooks, T. Hovatta, Y. Ishii, M. Kamada, T. Konstantinova, E. Kopatskaya, Yu. A. Kovalev, Y. Y. Kovalev, A. Lähteenmäki, L. Lanteri, J.-F. Le Campion, C.-U. Lee, P. Leto, H.-C. Lin, E. Lindfors, M. G. Mingaliev, S. Mizoguchi, F. Nicastro, M. G. Nikolashvili, S. Nishiyama, L. Östman, E. Ovcharov, P. Pääkkönen, M. Pasanen, E. Pian, T. Rector, J. A. Ros, K. Sadakane, J. H. Selj, E. Semkov, D. Sharapov, A. Somero, I. Stanev, A. Strigachev, L. Takalo, K. Tanaka, M. Tavani, I. Torniainen, M. Tornikoski, C. Trigilio, G. Umana, S. Vercellone, A. Valcheva, L. Volvach, M. Yamanaka, INAF - Osservatorio Astrofisico di Torino (OATo), Istituto Nazionale di Astrofisica (INAF), Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Observatoire aquitain des sciences de l'univers (OASU)
Subjects: Brightness, Astrophysics::High Energy Astrophysical Phenomena, galaxies: active, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Spectral line, [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], 0103 physical sciences, galaxies: quasars: individual: 3C 454.3, Astrophysics::Solar and Stellar Astrophysics, Blazar, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Line (formation), Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Astrophysics (astro-ph), Astronomy and Astrophysics, Light curve, Wavelength, Amplitude, galaxies: quasars: general, Space and Planetary Science, Radio frequency
Abstract: The blazar 3C 454.3 underwent an unprecedented optical outburst in spring 2005. This was first followed by a mm and then by a cm radio outburst, which peaked in February 2006. We report on follow-up observations by the WEBT to study the multiwavelength emission in the post-outburst phase. XMM-Newton observations on July and December 2006 added information on the X-ray and UV fluxes. The source was in a faint state. The radio flux at the higher frequencies showed a fast decreasing trend, which represents the tail of the big radio outburst. It was followed by a quiescent state, common at all radio frequencies. In contrast, moderate activity characterized the NIR and optical light curves, with a progressive increase of the variability amplitude with increasing wavelength. We ascribe this redder-when-brighter behaviour to the presence of a "little blue bump" due to line emission from the broad line region, which is clearly visible in the source SED during faint states. Moreover, the data from the XMM-Newton OM reveal a rise of the SED in the UV, suggesting the existence of a "big blue bump" due to thermal emission from the accretion disc. The X-ray spectra are well fitted with a power-law model with photoelectric absorption, possibly larger than the Galactic one. However, the comparison with previous X-ray observations would imply that the amount of absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum presents a curvature, which may depend on the X-ray brightness. In this case, two scenarios are possible., 9 pages, 7 figures, accepted for publication in A&A
Published: 2007

44. The radio delay of the exceptional 3C 454.3 outburst. Follow-up WEBT observations in 2005-2006

Author: M. Villata, C. M. Raiteri, M. F. Aller, U. Bach, M. A. Ibrahimov, Y. Y. Kovalev, O. M. Kurtanidze, V. M. Larionov, C.-U. Lee, P. Leto, A. Lähteenmäki, K. Nilsson, T. Pursimo, J. A. Ros, N. Sumitomo, A. Volvach, H. D. Aller, A. Arai, C. S. Buemi, J. M. Coloma, V. T. Doroshenko, Yu. S. Efimov, L. Fuhrmann, V. A. Hagen-Thorn, M. Kamada, M. Katsuura, T. Konstantinova, E. Kopatskaya, D. Kotaka, Yu. A. Kovalev, M. Kurosaki, L. Lanteri, L. Larionova, M. G. Mingaliev, S. Mizoguchi, K. Nakamura, M. G. Nikolashvili, S. Nishiyama, K. Sadakane, S. G. Sergeev, L. A. Sigua, A. Sillanpää, R. L. Smart, L. O. Takalo, K. Tanaka, M. Tornikoski, C. Trigilio, and G. Umana
Subjects: Physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Phase (waves), Flux, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Light curve, law.invention, Correlation function (statistical mechanics), symbols.namesake, Space and Planetary Science, law, symbols, Radio frequency, Blazar, Doppler effect, Flare
Abstract: In spring 2005 the blazar 3C 454.3 was observed in an unprecedented bright state from the near-IR to the hard X-ray frequencies. A mm outburst peaked in June-July 2005, and it was followed by a flux increase at high radio frequencies. In this paper we report on multifrequency monitoring by the WEBT aimed at following the further evolution of the outburst in detail. In particular, we investigate the expected correlation and time delays between the optical and radio emissions in order to derive information on the variability mechanisms and jet structure. A comparison among the light curves at different frequencies is performed by means of visual inspection and discrete correlation function, and the results are interpreted with a simple model taking into account Doppler factor variations of geometric origin. The high-frequency radio light curves show a huge outburst starting during the dimming phase of the optical one and lasting more than 1 year. The first phase is characterized by a slow flux increase, while in early 2006 a major flare is observed. The lower-frequency radio light curves show a progressively delayed and fainter event, which disappears below 8 GHz. We suggest that the radio major peak is not physically connected with the spring 2005 optical one, but it is actually correlated with a minor optical flare observed in October-November 2005. This interpretation involves both an intrinsic and a geometric mechanism. The former is represented by disturbances travelling down the emitting jet, the latter being due to the curved-jet motion, with the consequent differential changes of viewing angles of the different emitting regions., Comment: 5 pages, 3 figures, to be published in A&A (Letters)
Published: 2007
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45. A Possible Periodicity in the Radio Lightcurves of 3C454.3

Author: Shan-Jie Qian, N. A Kudryavtseva, S Britzen, T. P Krichbaum, Long Gao, A Witzel, J. A Zensus, M. F Aller, H. D Aller, and Xi-Zhen Zhang
Subjects: Physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Rest frame, symbols.namesake, Space and Planetary Science, Orbital motion, symbols, Astrophysics::Earth and Planetary Astrophysics, Doppler effect
Abstract: During the period 1966.5 - 2006.2 the 15GHz and 8GHz lightcurves of 3C454.3 (z=0.859) show a qsasi-periodicity of ~12.8 yr (~6.9 yr in the rest frame of the source) with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-jet model in which the two jets are created from the black holes in a binary system and rotate with the period of the orbital motion. The periodic variations in the radio fluxes of 3C454.3 are suggested to be mainly due to the lighthouse effects (or the variation in Doppler boosting) of the precessing jets which are caused by the orbital motion. In addition, variations in the mass-flow rates accreting onto the black holes may be also involved., Comment: 15 pages, 11 figures
Published: 2007
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46. Doppler Boosting, Superluminal Motion, and the Kinematics of AGN Jets

Author: Eduardo Ros, Matthew L. Lister, Marshall H. Cohen, Matthias Kadler, Margo F. Aller, Kenneth I. Kellermann, J. A. Zensus, Rene C. Vermeulen, Daniel C. Homan, H. D. Aller, and Yuri Y. Kovalev
Subjects: Physics, Brightness, Jet (fluid), Superluminal motion, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Luminosity, Lorentz factor, symbols.namesake, Relativistic plasma, 13. Climate action, Space and Planetary Science, Brightness temperature, 0103 physical sciences, symbols, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics
Abstract: We discuss results from a decade long program to study the fine-scale structure and the kinematics of relativistic AGN jets with the aim of better understanding the acceleration and collimation of the relativistic plasma forming AGN jets. From the observed distribution of brightness temperature, apparent velocity, flux density, time variability, and apparent luminosity, the intrinsic properties of the jets including Lorentz factor, luminosity, orientation, and brightness temperature are discussed. Special attention is given to the jet in M87, which has been studied over a wide range of wavelengths and which, due to its proximity, is observed with excellent spatial resolution. Most radio jets appear quite linear, but we also observe curved non-linear jets and non-radial motions. Sometimes, different features in a given jet appear to follow the same curved path but there is evidence for ballistic trajectories as well. The data are best fit with a distribution of Lorentz factors extending up to gamma ~30 and intrinsic luminosity up to ~10^26 W/Hz. In general, gamma-ray quasars may have somewhat larger Lorentz factors than non gamma-ray quasars. Initially the observed brightness temperature near the base of the jet extend up to ~5x10^13 K which is well in excess of the inverse Compton limit and corresponds to a large excess of particle energy over magnetic energy. However, more typically, the observed brightness temperatures are ~2x10^11 K, i.e., closer to equipartition., Comment: 10 pages, 12 color figures; proceedings of the 5th Stromlo Symposium: Disks, Winds, and Jets - from Planets to Quasars; accepted in Astrophysics & Space Science
Published: 2007
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47. Statistical analyses of long-term variability of AGN at high radio frequencies

Author: I. Torniainen, Margo F. Aller, Harry J. Lehto, Merja Tornikoski, Talvikki Hovatta, Markku Lainela, H. D. Aller, and Esko Valtaoja
Subjects: Physics, Active galactic nucleus, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Polarization (waves), Lorentz factor, symbols.namesake, Radio observatory, Space and Planetary Science, Statistical analyses, symbols, Radio frequency, Astrophysics::Galaxy Astrophysics
Abstract: We present a study of variability time scales in a large sample of Active Galactic Nuclei at several frequencies between 4.8 and 230 GHz. We investigate the differences of various AGN types and frequencies and correlate the measured time scales with physical parameters such as the luminosity and the Lorentz factor. Our sample consists of both high and low polarization quasars, BL Lacertae objects and radio galaxies. The basis of this work is the 22 GHz, 37 GHz and 87 GHz monitoring data from the Metsahovi Radio Observatory spanning over 25 years. In addition,we used higher 90 GHz and 230 GHz frequency data obtained with the SEST-telescope between 1987 and 2003. Further lower frequency data at 4.8 GHz, 8 GHz and 14.5 GHz from the University of Michigan monitoring programme have been used. We have applied three different statistical methods to study the time scales: The structure function, the discrete correlation function and the Lomb-Scargle periodogram. We discuss also the differences and relative merits of these three methods. Our study reveals that smaller flux density variations occur in these sources on short time scales of 1-2 years, but larger outbursts happen quite rarely, on the average only once in every 6 years. We do not find any significant differences in the time scales between the source classes. The time scales are also only weakly related to the luminosity suggesting that the shock formation is caused by jet instabilities rather than the central black hole., Comment: 19 pages, 12 figures, Accepted for publication in A&A
Published: 2007
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48. Optical and radio variability of BL Lacertae

Author: O. M. Kurtanidze, Maria G. Nikolashvili, A. E. Volvach, Alok C. Gupta, Haritma Gaur, A. Strigachev, H. D. Aller, I. Agudo, L. A. Sigua, Margo F. Aller, Aditi Agarwal, S. Peneva, Anne Lähteenmäki, L. N. Volvach, S. O. Kurtanidze, R. Bachev, Evgeni Semkov, Minfeng Gu, Paul J. Wiita, Merja Tornikoski, Anne Lähteenmäki Group, Department of Radio Science and Engineering, Aalto-yliopisto, and Aalto University
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, general [quasars], general [BL Lacertae objects], 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, jets [galaxies], FOS: Physical sciences, Flux, Astronomy and Astrophysics, Context (language use), Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Radio spectrum, Galaxy, 13. Climate action, Space and Planetary Science, Active phase, active [galaxies], 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Blazar, 010303 astronomy & astrophysics, individual: BL Lacertae [BL Lacertae objects]
Abstract: We observed the prototype blazar, BL Lacertae, extensively in optical and radio bands during an active phase in the period 2010--2013 when the source showed several prominent outbursts. We searched for possible correlations and time lags between the optical and radio band flux variations using multifrequency data to learn about the mechanisms producing variability. During an active phase of BL Lacertae, we searched for possible correlations and time lags between multifrequency light curves of several optical and radio bands. We tried to estimate any possible variability timescales and inter-band lags in these bands. We performed optical observations in B, V, R and I bands from seven telescopes in Bulgaria, Georgia, Greece and India and obtained radio data at 36.8, 22.2, 14.5, 8 and 4.8 GHz frequencies from three telescopes in Ukraine, Finland and USA. Significant cross-correlations between optical and radio bands are found in our observations with a delay of cm-fluxes with respect to optical ones of ~250 days. The optical and radio light curves do not show any significant timescales of variability. BL Lacertae showed many optical 'mini-flares' on short time-scales. Variations on longer term timescales are mildly chromatic with superposition of many strong optical outbursts. In radio bands, the amplitude of variability is frequency dependent. Flux variations at higher radio frequencies lead the lower frequencies by days or weeks. The optical variations are consistent with being dominated by a geometric scenario where a region of emitting plasma moves along a helical path in a relativistic jet. The frequency dependence of the variability amplitude supports an origin of the observed variations intrinsic to the source., Comment: 10 pages, 9 figures, Accepted for publication in A&A
Published: 2015
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49. Multifrequency variability of the blazar AO 0235+164. The WEBT campaign in 2004-2005 and long-term SED analysis

Author: C. M. Raiteri, M. Villata, M. Kadler, M. A. Ibrahimov, O. M. Kurtanidze, V. M. Larionov, M. Tornikoski, P. Boltwood, C.-U. Lee, M. F. Aller, G. E. Romero, H. D. Aller, A. T. Araudo, A. A. Arkharov, U. Bach, D. Barnaby, A. Berdyugin, C. S. Buemi, M. T. Carini, D. Carosati, S. A. Cellone, R. Cool, M. Dolci, N. V. Efimova, L. Fuhrmann, V. A. Hagen-Thorn, M. Holcomb, I. Ilyin, V. Impellizzeri, R. Z. Ivanidze, B. Z. Kapanadze, J. Kerp, T. S. Konstantinova, Y. Y. Kovalev, Yu. A. Kovalev, A. Kraus, T. P. Krichbaum, A. Lähteenmäki, L. Lanteri, P. Leto, E. Lindfors, J. R. Mattox, N. Napoleone, M. G. Nikolashvili, K. Nilsson, J. Ohlert, I. E. Papadakis, M. Pasanen, C. Poteet, T. Pursimo, E. Ros, L. A. Sigua, S. Smith, L. O. Takalo, C. Trigilio, M. Tröller, G. Umana, H. Ungerechts, R. Walters, A. Witzel, and E. Xilouris
Subjects: Ciencias Astronómicas, active [Galaxies], Galaxies: quasars: general, Ciencias Físicas, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, AO 0235+164 (objeto BL Lac), Spectral line, law.invention, Telescope, purl.org/becyt/ford/1 [https], law, Jets, quasars: general [Galaxies], Blazar, Quasars, Ciencias Exactas, Physics, Astrophysics (astro-ph), Spectral density, Astronomy and Astrophysics, Galaxies: active, purl.org/becyt/ford/1.3 [https], Galaxies: BL lacertae objects: individual: AO 0235+164, BL lacertae objects: general [Galaxies], Light curve, Astronomía, BL lacertae objects: individual: AO 0235+164 [Galaxies], Wavelength, Galaxies: jets, Space and Planetary Science, Active galaxies, BL Lacertae objects, jets [Galaxies], Satellite, Radio frequency, Galaxies: BL lacertae objects: general, CIENCIAS NATURALES Y EXACTAS
Abstract: Aims. A huge multiwavelength campaign targeting the blazar AO 0235+164 was organized by the Whole Earth Blazar Telescope (WEBT) in 2003-2005 to study the variability properties of the source. Methods. Monitoring observations were carried out at cm and mm wavelengths, and in the near-IR and optical bands, while three pointings by the XMM-Newton satellite provided information on the X-ray and UV emission. Results. We present the data acquired during the second observing season, 2004-2005, by 27 radio-to-optical telescopes. The ∼2600 data points collected allow us to trace the low-energy behaviour of the source in detail, revealing an increased near-IR and optical activity with respect to the previous season. Increased variability is also found at the higher radio frequencies, down to ∼15 GHz, but not at the lower ones. While the X-ray (and optical) light curves obtained during the XMM-Newton pointings reveal no significant short-term variability, the simultaneous intraday radio observations with the 100 m telescope at Effelsberg show flux-density changes at 10.5 GHz, which are more likely due to a combination of intrinsic and extrinsic processes. Conclusions. The radio (and optical) outburst predicted to peak around February-March 2004 on the basis of the previously observed 5-6 yr quasi-periodicity did not occur. The analysis of the optical light curves reveals now a longer characteristic time scale of variability of ∼8 yr, which is also present in the radio data. The spectral energy distributions corresponding to the XMM-Newton observations performed during the WEBT campaign are compared with those pertaining to previous pointings of X-ray satellites. Bright, soft X-ray spectra can be described in terms of an extra component, which appears also when the source is faint through a hard UV spectrum and a curvature of the X-ray spectrum. Finally, there might be a correlation between the X-ray and optical bright states with a long time delay of about 5 yr, which would require a geometrical interpretation., La lista completa de autores que integran el documento puede consultarse en el archivo., Facultad de Ciencias Astronómicas y Geofísicas
Published: 2006

50. A historic jet-emission minimum reveals hidden spectral features in 3C 273

Author: Marc Türler, Margo F. Aller, H. D. Aller, Ian M. McHardy, Thierry J.-L. Courvoisier, P. T. O'Brien, Maria Chernyakova, C. Foellmi, K. L. Page, Alex Kraus, Thomas P. Krichbaum, Alan P. Marscher, Anne Lähteenmäki, L. Popescu, E. I. Robson, H. Ungerechts, Merja Tornikoski, Laboratoire d'Astrophysique de Grenoble (LAOG), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Physics, Jet (fluid), 010308 nuclear & particles physics, Infrared, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Quasar, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Synchrotron, law.invention, Rotating black hole, Space and Planetary Science, law, 0103 physical sciences, Thermal, Millimeter, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Line (formation)
Abstract: Aims. The aim of this work is to identify and study spectral features in the quasar 3C 273 usually blended by its strong jet emission. Method. A historic minimum in the sub-millimetre emission of 3C 273 triggered coordinated multi-wavelength observations in June 2004. X-ray observations from the INTEGRAL, XMM-Newton and RXTE satellites are complemented by ground-based optical, infrared, millimetre and radio observations. The overall spectrum is used to model the infrared and X-ray spectral components. Results. Three thermal dust emission components are identified in the infrared. The dust emission on scales from 1 pc to several kpc is comparable to that of other quasars, as expected by AGN unification schemes. The observed weakness of the X-ray emission supports the hypothesis of a synchrotron self-Compton origin for the jet component. There is a clear soft-excess and we find evidence for a very broad iron line which could be emitted in a disk around a Kerr black hole. Other signatures of a Seyfert-like X-ray component are not detected., 4 pages. Accepted for publication in A&A Letters
Published: 2006
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