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29 results on '"Madejski, Greg M."'

1. MERGER-DRIVEN FUELING OF ACTIVE GALACTIC NUCLEI: SIX DUAL AND OF AGNs DISCOVERED WITH CHANDRA AND HUBBLE SPACE TELESCOPE OBSERVATIONS

Author

Comerford, Julia M, Pooley, David, Barrows, R Scott, Greene, Jenny E, Zakamska, Nadia L, Madejski, Greg M, and Cooper, Michael C

Subjects
astro-ph.GA, astro-ph.CO, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Physical Chemistry (incl. Structural), Astronomy & Astrophysics
Abstract

Dual active galactic nuclei (AGNs) and offset AGNs are kpc-scale separation supermassive black holes pairs created during galaxy mergers, where both or one of the black holes are AGNs, respectively. These dual and offset AGNs are valuable probes of the link between mergers and AGNs but are challenging to identify. Here we present Chandra/ACIS observations of 12 optically selected dual AGN candidates at z < 0.34, where we use the X-rays to identify AGNs. We also present Hubble Space Telescope/Wide Field Camera 3 observations of 10 of these candidates, which reveal any stellar bulges accompanying the AGNs. We discover a dual AGN system with separation δx = 2.2 kpc, where the two stellar bulges have coincident [O iii] λ5007 and X-ray sources. This system is an extremely minor merger (460:1) that may include a dwarf galaxy hosting an intermediate mass black hole. We also find six single AGNs, and five systems that are either dual or offset AGNs with separations δx < 10 kpc. Four of the six dual AGNs and dual/offset AGNs are in ongoing major mergers, and these AGNs are 10 times more luminous, on average, than the single AGNs in our sample. This hints that major mergers may preferentially trigger higher luminosity AGNs. Further, we find that confirmed dual AGNs have hard X-ray luminosities that are half of those of single AGNs at fixed [O iii] λ5007 luminosity, on average. This could be explained by high densities of gas funneled to galaxy centers during mergers, and emphasizes the need for deeper X-ray observations of dual AGN candidates.

Published
2015

2. SYSTEMATIC STUDY OF GAMMA-RAY-BRIGHT BLAZARS WITH OPTICAL POLARIZATION AND GAMMA-RAY VARIABILITY

Author

Itoh, Ryosuke, primary, Nalewajko, Krzysztof, additional, Fukazawa, Yasushi, additional, Uemura, Makoto, additional, Tanaka, Yasuyuki T., additional, Kawabata, Koji S., additional, Madejski, Greg M., additional, Schinzel, Frank. K., additional, Kanda, Yuka, additional, Shiki, Kensei, additional, Akitaya, Hiroshi, additional, Kawabata, Miho, additional, Moritani, Yuki, additional, Nakaoka, Tatsuya, additional, Ohsugi, Takashi, additional, Sasada, Mahito, additional, Takaki, Katsutoshi, additional, Takata, Koji, additional, Ui, Takahiro, additional, Yamanaka, Masayuki, additional, and Yoshida, Michitoshi, additional

Published
2016
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3. 3C 273 WITHNuSTAR: UNVEILING THE ACTIVE GALACTIC NUCLEUS

Author

Madsen, Kristin K., primary, Fürst, Felix, additional, Walton, Dominic J., additional, Harrison, Fiona A., additional, Nalewajko, Krzysztof, additional, Ballantyne, David R., additional, Boggs, Steve E., additional, Brenneman, Laura W., additional, Christensen, Finn E., additional, Craig, William W., additional, Fabian, Andrew C., additional, Forster, Karl, additional, Grefenstette, Brian W., additional, Guainazzi, Matteo, additional, Hailey, Charles J., additional, Madejski, Greg M., additional, Matt, Giorgio, additional, Stern, Daniel, additional, Walter, Roland, additional, and Zhang, William W., additional

Published
2015
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5. THE VARIABLE HARD X-RAY EMISSION OF NGC 4945 AS OBSERVED BYNUSTAR

Author

Puccetti, Simonetta, primary, Comastri, Andrea, additional, Fiore, Fabrizio, additional, Arévalo, Patricia, additional, Risaliti, Guido, additional, Bauer, Franz E., additional, Brandt, William N., additional, Stern, Daniel, additional, Harrison, Fiona A., additional, Alexander, David M., additional, Boggs, Steve E., additional, Christensen, Finn E., additional, Craig, William W., additional, Gandhi, Poshak, additional, Hailey, Charles J., additional, Koss, Michael J., additional, Lansbury, George B., additional, Luo, Bin, additional, Madejski, Greg M., additional, Matt, Giorgio, additional, Walton, Dominic J., additional, and Zhang, Will, additional

Published
2014
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8. THENUCLEAR SPECTROSCOPIC TELESCOPE ARRAY(NuSTAR) HIGH-ENERGY X-RAY MISSION

Author

Harrison, Fiona A., primary, Craig, William W., additional, Christensen, Finn E., additional, Hailey, Charles J., additional, Zhang, William W., additional, Boggs, Steven E., additional, Stern, Daniel, additional, Cook, W. Rick, additional, Forster, Karl, additional, Giommi, Paolo, additional, Grefenstette, Brian W., additional, Kim, Yunjin, additional, Kitaguchi, Takao, additional, Koglin, Jason E., additional, Madsen, Kristin K., additional, Mao, Peter H., additional, Miyasaka, Hiromasa, additional, Mori, Kaya, additional, Perri, Matteo, additional, Pivovaroff, Michael J., additional, Puccetti, Simonetta, additional, Rana, Vikram R., additional, Westergaard, Niels J., additional, Willis, Jason, additional, Zoglauer, Andreas, additional, An, Hongjun, additional, Bachetti, Matteo, additional, Barrière, Nicolas M., additional, Bellm, Eric C., additional, Bhalerao, Varun, additional, Brejnholt, Nicolai F., additional, Fuerst, Felix, additional, Liebe, Carl C., additional, Markwardt, Craig B., additional, Nynka, Melania, additional, Vogel, Julia K., additional, Walton, Dominic J., additional, Wik, Daniel R., additional, Alexander, David M., additional, Cominsky, Lynn R., additional, Hornschemeier, Ann E., additional, Hornstrup, Allan, additional, Kaspi, Victoria M., additional, Madejski, Greg M., additional, Matt, Giorgio, additional, Molendi, Silvano, additional, Smith, David M., additional, Tomsick, John A., additional, Ajello, Marco, additional, Ballantyne, David R., additional, Baloković, Mislav, additional, Barret, Didier, additional, Bauer, Franz E., additional, Blandford, Roger D., additional, Brandt, W. Niel, additional, Brenneman, Laura W., additional, Chiang, James, additional, Chakrabarty, Deepto, additional, Chenevez, Jerome, additional, Comastri, Andrea, additional, Dufour, Francois, additional, Elvis, Martin, additional, Fabian, Andrew C., additional, Farrah, Duncan, additional, Fryer, Chris L., additional, Gotthelf, Eric V., additional, Grindlay, Jonathan E., additional, Helfand, David J., additional, Krivonos, Roman, additional, Meier, David L., additional, Miller, Jon M., additional, Natalucci, Lorenzo, additional, Ogle, Patrick, additional, Ofek, Eran O., additional, Ptak, Andrew, additional, Reynolds, Stephen P., additional, Rigby, Jane R., additional, Tagliaferri, Gianpiero, additional, Thorsett, Stephen E., additional, Treister, Ezequiel, additional, and Urry, C. Megan, additional

Published
2013
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23. Implications of Variability Patterns Observed in TeV Blazars on the Structure of the Inner Jet

Author

Madejski, Greg M., Tanihata, Chiharu, Takahashi, Tadayuki, and Kataoka, Jun

Subjects
Physics, Jet (fluid), Scale (ratio), Lorentz transformation, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Sigma, Astronomy and Astrophysics, Context (language use), Astrophysics, Light curve, Shock (mechanics), symbols.namesake, Space and Planetary Science, symbols, Blazar
Abstract

The recent long look X-ray observations of TeV blazars have revealed many important new features concerning their time variability. In this paper, we suggest a physical interpretation for those features based on the framework of the internal and external shock scenarios. We present a simplified model applicable to TeV blazars, and investigate through simulations how each of the model parameters would affect to the observed light curve or spectrum. In particular, we show that the internal shock scenario naturally leads to all the observed variability properties including the structure function, but for it to be applicable, the fractional fluctuation of the initial bulk Lorentz factors must be small, with sigma_gamma / gamma_average < 0.01. This implies very low dynamical efficiency of the internal shock scenario. We also suggest that several observational quantities -- such as the characteristic time scale, the relative amplitude of flares as compared to the steady (``offset'') component, and the slope of the structure function -- can be used to probe the inner jet. The results are applied to the TeV blazar Mrk421, and this, within the context of the model, leads to the determination of several physical parameters: the ejection of a shell with average thickness of ~1E13 cm occurs on average every 10 minutes, and the shells collide ~1E17 cm away from the central source., 12 pages, 13 figures, to appear in ApJ

Published
2003

26. Simultaneous Chandra and Rossi X-Ray Timing Explorer Observations of the Nearby Bright Seyfert 2 Galaxy NGC 4945

Author

Done, Chris, Madejski, Greg M., Zycki, Piotr T., and Greenhill, Lincoln J.

Abstract

We analyze recent simultaneous Chandra/RXTE observations of the Seyfert 2 galaxy NGC 4945. The unprecedented spatial resolution of Chandra means we are able to separate the spectra of the nucleus, starburst, and superwind regions, while the RXTE data extend the spectrum to higher energies. The extreme absorbing column of NH ~ 4 x 1024 cm-2 means that the nucleus is only directly seen above 8-10 keV, while the lower energy spectrum from the nuclear region in Chandra is dominated by reflection. By contrast, the superwind is dominated by emission from hot plasma, but the starburst region contains both hot plasma and reflection signatures. Forming a reflected spectrum requires that the starburst region contain clumps of cool, optically thick material, perhaps star-forming cores, which are irradiated by 7-10 keV photons from the nucleus. Since photons of this energy are obscured along the line of sight, this confirms the result of Madejski et al. that the extreme absorption material is disklike rather than toroidal. However, the IR/optical limits on the lack of high-excitation emission lines show that, by contrast, the lower energy photons from the nucleus are obscured in all directions. We discuss the complex absorption structure revealed by these observations and propose an overall source geometry in which the nucleus is completely embedded in material with NH ~ 1023 cm-2.

Published
2003

27. Variability Timescales of TeV Blazars Observed in the ASCA Continuous Long-Look X-Ray Monitoring

Author

Tanihata, Chiharu, Urry, Megan, Takahashi, Tadayuki, Kataoka, Jun, Wagner, Stefan J., Madejski, Greg M., Tashiro, Makoto, and Kouda, Manabu

Abstract

Three uninterrupted, long (lasting respectively 7, 10, and 10 days) ASCA observations of the well-studied TeV-bright blazars Mrk 421, Mrk 501, and PKS 2155-304 all show continuous strong X-ray flaring. Despite the relatively faint intensity states in two of the three sources, there was no identifiable quiescent period in any of the observations. Structure function analysis shows that all blazars have a characteristic timescale of ~1 day, comparable to the recurrence time and to the timescale of the stronger flares. On the other hand, examination of these flares in more detail reveals that each of the strong flares is not a smooth increase and decrease but exhibits substructures of shorter flares having timescales of ~10 ks. We verify via simulations that in order to explain the observed structure function, these shorter flares ("shots") are unlikely to be fully random, but in some way are correlated with each other. The energy dependent cross-correlation analysis shows that interband lags are not universal in TeV blazars. This is important since in the past only positive detections of lags were reported. In this work, we determine that the sign of a lag may differ from flare to flare; significant lags of both signs were detected from several flares, while no significant lag was detected from others. However, we also argue that the nature of the underlying component can affect these values. The facts that all flares are nearly symmetric and that fast variability shorter than the characteristic timescale is strongly suppressed, support the scenario where the light crossing time dominates the variability timescales of the day-scale flares.

Published
2001

29. 3C 273 WITHNuSTAR: UNVEILING THE ACTIVE GALACTIC NUCLEUS

Author

Dominic J. Walton, Karl Forster, William W. Craig, Andrew C. Fabian, Giorgio Matt, Fiona A. Harrison, Charles J. Hailey, Brian W. Grefenstette, Greg Madejski, S. E. Boggs, Laura Brenneman, Finn Erland Christensen, Matteo Guainazzi, Felix Fürst, Daniel Stern, Kristin K. Madsen, Krzysztof Nalewajko, William W. Zhang, Roland Walter, David R. Ballantyne, Madsen, Kristin K., Fürst, Felix, Walton, Dominic J., Harrison, Fiona A., Nalewajko, Krzysztof, Ballantyne, David R., Boggs, Steve E., Brenneman, Laura W., Christensen, Finn E., Craig, William W., Fabian, Andrew C., Forster, Karl, Grefenstette, Brian W., Guainazzi, Matteo, Hailey, Charles J., Madejski, Greg M., Matt, Giorgio, Stern, Daniel, Walter, Roland, and Zhang, William W.

Subjects
Physics, Nuclear and High Energy Physics, Photon, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, Extrapolation, Astronomy and Astrophysics, Quasar, Astrophysics, individual (3C 273) [X-rays], Power law, Accretion (astrophysics), Spectral line, Space and Planetary Science, individual (3C 273) [quasars], Fermi Gamma-ray Space Telescope
Abstract

We present results from a 244 ks NuSTAR observation of 3C 273 obtained during a cross-calibration campaign with the Chandra, INTEGRAL, Suzaku, Swift, and XMM-Newton observatories. We show that the spectrum, when fit with a power-law model using data from all observatories except INTEGRAL over the 1-78 keV band, leaves significant residuals in the NuSTAR data between 30 and 78 keV. The NuSTAR 3-78 keV spectrum is well. described by an exponentially cutoff power law (Γ = 1.646± 0.006, Ecutoff = 202-34 +51 keV) with a weak reflection component from cold, dense material. There is also evidence for a weak (EW = 23 ± 11 eV) neutral iron line. We interpret these features as arising from coronal emission plus reflection off an accretion disk or distant material. Beyond 80 keV INTEGRAL data show clear excess flux relative to an extrapolation of the active galactic nucleus model fit to NuSTAR. This high-energy power. law is consistent with the presence of a beamed jet, which begins to dominate over emission from the inner accretion flow at 30-40 keV. Modeling the jet locally (in the NuSTAR + INTEGRAL band) as a power. law, we find that the coronal component is fit by ΓAGN = 1.638 ± 0.045, Ecutoff = 47 ± 15 keV, and jet photon index by Γjet = 1.05 ± 0.4. We also consider Fermi/LAT observations of 3C 273, and here the broadband spectrum of the jet can be described by a log-parabolic model, peaking at ∼ 2 MeV. Finally, we investigate the spectral variability in the NuSTAR band and find an inverse correlation between flux and Gamma.

Published
2015
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