Search

We present the most extensive and well-sampled long-term multi-band near-infrared (NIR) temporal and spectral variability study of OJ 287, considered to be the best candidate binary supermassive black hole blazar. These observations were made between December 2007 and November 2021. The source underwent ~ 2 -- 2.5 magnitude variations in the J, H, and Ks NIR bands. Over these long-term timescales there were no systematic trends in either flux or spectral evolution with time or with the source's flux states. However, on shorter timescales, there are significant variations in flux and spectra indicative of strong changes during different activity states. The NIR spectral energy distributions show diverse facets at each flux state, from the lowest to the highest. The spectra are, in general, consistent with a power-law spectral profile (within 10%) and many of them indicate minor changes (observationally insignificant) in the shift of the peak. The NIR spectra generally steepens during bright phases. We briefly discuss these behaviors in the context of blazar emission scenarios/mechanisms, OJ 287's well-known traditional behavior, and implications for models of the source central engine invoked for its long-term optical semi-periodic variations., Comment: 17 pages, 6 figures, 5 tables. Accepted for publication in ApJS

Context. QSO B1420+326 is a blazar classified as a Flat Spectrum Radio Quasar (FSRQ). In the beginning of 2020 it underwent an enhanced flux state. An extensive multiwavelength campaign allowed us to trace the evolution of the flare. Aims. We search for VHE gamma-ray emission from QSO B1420+326 during this flaring state. We aim to characterize and model the broadband emission of the source over different phases of the flare. Methods. The source was observed with a number of instruments in radio, near infrared, optical (including polarimetry and spectroscopy), ultra-violet, X-ray and gamma-ray bands. We use dedicated optical spectroscopy results to estimate the accretion disk and the dust torus luminosity. We perform spectral energy distribution modeling in the framework of combined Synchrotron-Self-Compton and External Compton scenario in which the electron energy distribution is partially determined from acceleration and cooling processes. Results. During the enhanced state the flux of both SED components drastically increased and the peaks were shifted to higher energies. Follow up observations with the MAGIC telescopes led to the detection of very-high-energy gamma-ray emission from this source, making it one of only a handful of FSRQs known in this energy range. Modeling allows us to constrain the evolution of the magnetic field and electron energy distribution in the emission region. The gamma-ray flare was accompanied by a rotation of the optical polarization vector during a low polarization state. Also, a new, superluminal radio knot contemporaneously appeared in the radio image of the jet. The optical spectroscopy shows a prominent FeII bump with flux evolving together with the continuum emission and a MgII line with varying equivalent width., Comment: 20 pages, 15 figures, 7 tables, accepted for publication in A&A

Ever since their discovery, Infrared dark clouds (IRDCs) are generally considered to be the sites just at the onset of high-mass (HM) star formation. In recent years, it has been realized that not all IRDCs harbour HM Young Stellar Objects (YSOs). Only those IRDCs satisfying a certain mass-size criterion, or equivalently above a certain threshold density, are found to contain HMYSOs. In all cases, IRDCs provide ideal conditions for the formation of stellar clusters. In this paper, we study the massive stellar content of IRDCs to re-address the relation between IRDCs and HM star formation. For this purpose, we have identified all IRDCs associated to a sample of 12 Galactic molecular clouds (MCs). The selected MCs have been the target of a systematic search for YSOs in an earlier study. The catalogued positions of YSOs have been used to search all YSOs embedded in each identified IRDC. In total, we have found 834 YSOs in 128 IRDCs. The sample of IRDCs have mean surface densities of 319 Mo/pc2, mean mass of 1062 Mo, and a mass function power-law slope -1.8, which are similar to the corresponding properties for the full sample of IRDCs and resulting physical properties in previous studies. We find that all those IRDCs containing at least one intermediate to high-mass young star satisfy the often-used mass-size criterion for forming HM stars. However, not all IRDCs satisfying the mass-size criterion contain HM stars. We find that the often used mass-size criterion corresponds to 35% probability of an IRDC forming a massive star. Twenty five (20%) of the IRDCs are potential sites of stellar clusters of mass more than 100 Mo., Comment: 9 pages. Accepted for publication in ApJ

We present a near-infrared imaging polarimetric study of the pre-planetary nebula: Frosty Leo. The observations were carried out in J, H and K' bands using the new polarimeter POLICAN mounted on the 2.1m telescope of the Guillermo Haro Astrophysical Observatory, Sonora, Mexico. The most prominent result observed in the polarization maps is a large and well defined dusty envelope (35\arcsec\ diameter in H-band). The polarization position angles in the envelope are particularly well ordered and nearly parallel to the equator of the nebula (seen in J and H bands). The nebula presents a known bipolar outflow and the envelope completely wraps around it. Within the bipolar lobes, we find high polarization levels ranging from $60\%$ (J band) to $90\%$ (K' band) and the polarization angles trace a centrosymmetric pattern. We found the remnants of superwind shells at the edges of the bipolar lobes and the duration of this phase is around 600 yrs. The origin of polarization features in the nebula is most likely due to a combination of single and multiple scattering. Our results clearly demonstrate new structures that provide new hints on the evolution of Frosty Leo from its previous asymptotic giant branch phase., Comment: 5 figures, 9 pages, accepted in MNRAS

Here we present the long-term optical spectral monitoring of a changing-look active galactic nuclei (AGN) NGC 3516 that covers 22 years (from 1996 to 2018). We explore a variability in the broad lines and continuum, finding that the continuum is changing by more than a factor of 2, while the broad lines are varying by more than a factor of 10. The minimum of activity is observed in 2014, when the broad lines almost disappeared. We confirm that NGC 3516 is a changing-look AGN, and the absorption seen in the UV and X-ray may indicate that there is an obscuring region which is responsible for this. The line profiles are also changing. The mean profiles of the broad Halpha and Hbeta lines show shoulder-like structure in the wings, and enhanced peak, that may indicate a complex BLR. The rms-profiles of both lines seem to have the same shape and width of around 4200 km/s, indicating practically the same kinematics in the Halpha and Hbeta emitting regions. Measured time-lags between the continuum and Halpha and Hbeta broad-line variability are ~15 and 17 days, respectively, that in combination with the broad lines width allows us to estimate the NGC 3516 central black hole mass. We find that the black hole mass is 4.73+-1.40 x 10^7M_sun which is in agreement with previous estimates., Comment: Accepted for publication in MNRAS

We report on the coexistence of powerful gas outflows observed in millimeter and X-ray data of the Radio-Loud Narrow Line Seyfert 1 Galaxy IRAS 17020+4544. Thanks to the large collecting power of the Large Millimeter Telescope, a prominent line arising from the 12CO(1-0) transition was revealed in recent observations of this source. The complex profile is composed by a narrow double-peak line and a broad wing. While the double-peak structure may be arising in a disk of molecular material, the broad wing is interpreted as the signature of a massive outflow of molecular gas with an approximate bulk velocity of -660 km/s. This molecular wind is likely associated to a multi-component X-ray Ultra-Fast Outflow with velocities reaching up to ~0.1c and column densities in the range 10^{21-23.9} cm^-2 that was reported in the source prior to the LMT observations. The momentum load estimated in the two gas phases indicates that within the observational uncertainties the outflow is consistent with being propagating through the galaxy and sweeping up the gas while conserving its energy. This scenario, which has been often postulated as a viable mechanism of how AGN feedback takes place, has so far been observed only in ULIRGs sources. IRAS 17020+4544 with bolometric and infrared luminosity respectively of 5X10^{44} erg/s and 1.05X10^{11} L_sun appears to be an example of AGN feedback in a NLSy1 Galaxy (a low power AGN). New proprietary multi-wavelength data recently obtained on this source will allow us to corroborate the proposed hypothesis., Comment: Accepted for publication on ApJ Letters, 9 pages, 4 figures

In this paper, we present light curves for 3C 279 over a time period of six years; from 2008 to 2014. Our multiwavelength data comprise 1 mm to gamma-rays, with additional optical polarimetry. Based on the behaviour of the gamma-ray light curve with respect to other bands, we identified three different activity periods. One of the activity periods shows anomalous behaviour with no gamma-ray counterpart associated with optical and NIR flares. Another anomalous activity period shows a flare in gamma-rays, 1 mm and polarization degree, however, it does not have counterparts in the UV continuum, optical and NIR bands. We find a significant overall correlation of the UV continuum emission, the optical and NIR bands. This correlation suggests that the NIR to UV continuum is co-spatial. We also find a correlation between the UV continuum and the 1 mm data, which implies that the dominant process in producing the UV continuum is synchrotron emission. The gamma-ray spectral index shows statistically significant variability and an anti-correlation with the gamma-ray luminosity. We demonstrate that the dominant gamma-ray emission mechanism in 3C 279 changes over time. Alternatively, the location of the gamma-ray emission zone itself may change depending on the activity state of the central engine., Comment: 32 pages, 19 figures, Accepted for publication in MNRAS

Flat spectrum radio quasars (FSRQs) can suffer strong absorption above E = 25/(1+z) GeV, due to gamma-gamma interaction if the emitting region is at sub-parsec scale from the super-massive black hole (SMBH). Gamma-ray flares from these astrophysical sources can investigate the location of the high-energy emission region and the physics of the radiating processes. We present a remarkable gamma-ray flaring activity from FSRQ PKS 2023-07 during April 2016, as detected by both AGILE and Fermi satellites. An intensive multi-wavelength campaign, triggered by Swift, covered the entire duration of the flaring activity, including the peak gamma-ray activity. We report the results of multiwavelength observations of the blazar. We found that, during the peak emission, the most energetic photon had an energy of 44 GeV, putting strong constraints on the opacity of the gamma-ray dissipation region. The overall Spectral Energy Distribution (SED) is interpreted in terms of leptonic models for blazar jet, with the emission site located beyond the Broad Line Region (BLR).

POLICAN is a near-infrared imaging linear polarimeter developed for the Cananea Near-infrared Camera (CANICA) at the 2.1m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, Mexico. POLICAN is mounted ahead of CANICA and consist of a rotating super-achromatic 1-2.7 micron half-wave plate (HWP) as the modulator and a fixed wire-grid polarizer as the analyzer. CANICA has a 1024 x 1024 HgCdTe detector with a plate scale of 0.32 arcsec/pixel and provides a field of view of 5.5 x 5.5 arcmin^2. The polarimetric observations are carried out by modulating the incoming light through different steps of half-wave plate angles 0, 22.5, 45, 67.5 deg, to establish linear Stokes parameters (I, Q, and U). Image reduction consists of dark subtraction, polarimetric flat fielding, and sky subtraction. The astrometry and photometric calibrations are performed using the publicly available data from the Two Micron All Sky Survey. Polarimetric calibration includes observations of globular clusters and polarization standards available in the literature. Analysis of multiple observations of globular clusters yielded an instrumental polarization of 0.51%. Uncertainties in polarization range from 0.1% to 10% from the brightest 7 mag to faintest 16 mag stars. The polarimetric accuracy achieved is better than 0.5% and the position angle errors less than 5 deg for stars brighter than 13 mag in H-band. POLICAN is mainly being used to study the scattered polarization and magnetic fields in and around star-forming regions of the interstellar medium., Comment: Accepted for PASP, 23 pages

We present details of characterization and imaging performance of the Cananea Near-infrared camera (CANICA) at the 2.1m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, Mexico. CANICA has a HAWAII array with a HgCdTe detector of 1024 x 1024 pixels covering a field of view of 5.5 x 5.5 arcmin^2 with a plate scale of 0.32 arcsec/pixel. The camera characterization involved measuring key detector parameters: conversion gain, dark current, readout noise, and linearity. The pixels in the detector have a full-well-depth of 100,000 e- with the conversion gain measured to be 5.8 e-/ADU. The time-dependent dark current was estimated to be 1.2 e-/sec. Readout noise for correlated double sampled (CDS) technique was measured to be 30 e-/pixel. The detector shows 10% non-linearity close to the full-well-depth. The non-linearity was corrected within 1% levels for the CDS images. Full-field imaging performance was evaluated by measuring the point spread function, zeropoints, throughput, and limiting magnitude. The average zeropoint value in each filter are J = 20.52, H = 20.63, and K = 20.23. The saturation limit of the detector is about sixth magnitude in all the primary broadbands. CANICA on the 2.1m OAGH telescope reaches background-limited magnitudes of J = 18.5, H = 17.6, and K = 16.0 for a signal-to-noise ratio of 10 with an integration time of 900s., Comment: Accepted for PASP, 18 pages

We study the star formation (SF) law in 12 Galactic molecular clouds with ongoing high-mass star formation (HMSF) activity, as traced by the presence of a bright IRAS source and other HMSF tracers. We define the molecular cloud (MC) associated to each IRAS source using 13CO line emission, and count the young stellar objects (YSOs) within these clouds using GLIMPSE and MIPSGAL 24 micron Spitzer databases.The masses for high luminosity YSOs (Lbol>10~Lsun) are determined individually using Pre Main Sequence evolutionary tracks and the evolutionary stages of the sources, whereas a mean mass of 0.5 Msun was adopted to determine the masses in the low luminosity YSO population. The star formation rate surface density (sigsfr) corresponding to a gas surface density (siggas) in each MC is obtained by counting the number of the YSOs within successive contours of 13CO line emission. We find a break in the relation between sigsfr and siggas, with the relation being power-law (sigsfr ~ siggas^N) with the index N varying between 1.4 and 3.6 above the break. The siggas at the break is between 150-360 Msun/pc^2 for the sample clouds, which compares well with the threshold gas density found in recent studies of Galactic star-forming regions. Our clouds treated as a whole lie between the Kennicutt (1998) relation and the linear relation for Galactic and extra-galactic dense star-forming regions. We find a tendency for the high-mass YSOs to be found preferentially in dense regions at densities higher than 1200 Msun/pc^2 (~0.25 g/cm^2)., Comment: 21 pages, To appear in ApJ

We present the results of the long-term (20-year period, from 1996 to 2015) optical spectral monitoring of the Seyfert 1 galaxy NGC 7469. The variation in the light-curves of the broad He II {\lambda}4686A H{\beta} and H{\alpha} lines, and the continuum at 5100A and 6300A have been explored. The maximum of activity was in 1998, and the variability in the continuum and lines seems to have two periods of around 1200 and 2600 days, however these periodicities should be taken with caution because of the red-noise. Beside these periods, there are several short-term (1-5 days) flare-like events in the light-curves. There are good correlations between the continuum fluxes and H{\alpha} and H{\beta} line fluxes, but significantly smaller correlation between the He II and continuum. We found that the time-lags between the continuum and broad lines are different for H{\beta} (~20 l.d.) and H{\alpha} (~3 l.d.), and that He II also has a smaller lag (~2-3 l.d.). The H{\alpha} and H{\beta} line profiles show a slight red asymmetry, and the broad line profiles did not changed in the 20-year period. Using the lags and widths of H{\alpha} and H{\beta} we estimated the central black hole mass and found that it is ~(1-6)x$10^7 M_{\odot}$, which is in agreement with previous reverberation estimates., Comment: Accepted in Monthly Notices of the Royal Astronomical Society

We present an extensive study of the BL Lac object Mrk 501 based on a data set collected during the multi-instrument campaign spanning from 2009 March 15 to 2009 August 1 which includes, among other instruments, MAGIC, VERITAS, Whipple 10-m, Fermi-LAT, RXTE, Swift, GASP-WEBT and VLBA. We find an increase in the fractional variability with energy, while no significant interband correlations of flux changes are found in the acquired data set. The higher variability in the very high energy (>100 GeV, VHE) gamma-ray emission and the lack of correlation with the X-ray emission indicate that the highest-energy electrons that are responsible for the VHE gamma-rays do not make a dominant contribution to the ~1 keV emission. Alternatively, there could be a very variable component contributing to the VHE gamma-ray emission in addition to that coming from the synchrotron self-Compton (SSC) scenarios. The space of SSC model parameters is probed following a dedicated grid-scan strategy, allowing for a wide range of models to be tested and offering a study of the degeneracy of model-to-data agreement in the individual model parameters. We find that there is some degeneracy in both the one-zone and the two-zone SSC scenarios that were probed, with several combinations of model parameters yielding a similar model-to-data agreement, and some parameters better constrained than others. The SSC model grid-scan shows that the flaring activity around 2009 May 22 cannot be modeled adequately with a one-zone SSC scenario, while it can be suitably described within a two-independent-zone SSC scenario. The observation of an electric vector polarization angle rotation coincident with the gamma-ray flare from 2009 May 1 resembles those reported previously for low frequency peaked blazars, hence suggesting that there are many similarities in the flaring mechanisms of blazars with different jet properties., Comment: 33 pages, 15 figures, accepted for publication in A&A. Corresponding authors: Marlene Doert (marlene.doert@tu-dortmund.de) and David Paneque (dpaneque@mppmu.mpg.de)

In search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we performed a multi-wavelength campaign, in the X-ray band with Swift and XMM-Newton, performed infrared, optical (with OAGH, ESO-NTT and IAC80) and radio (ATCA) observations, as well as analysed archival hard X-ray data taken by INTEGRAL. We report on three X-ray sources consistent with the position of the Fermi-LAT source. We confirm the identification of the brightest object, RX J0838-2827, as a magnetic cataclysmic variable, that we recognize as an asynchronous system (not associated with the Fermi-LAT source). RX J0838-2827, is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as due to the binary system orbital period of ~1.64h and the white dwarf spin period of ~1.47h. A strong flux modulation at ~15h is observed at all energy bands, consistent with the beat frequency between spin and orbital periods. Optical spectra show prominent Hbeta, HeI and HeII emission lines Doppler-modulated at the orbital period and at the beat period. Therefore, RX J0838-2827, accretes through a diskless configuration and could be either a strongly asynchronous polar or a rare example of a pre-polar system in its way to reach synchronism. Among the other two X-ray sources, XMM J083850.4-282759 showed a variable X-ray emission, with a powerful flare lasting ~600s, similar to what is observed in transitional millisecond pulsars during the sub-luminous disc state: that would possibly associate this source with the Fermi-LAT source., Comment: 19 pages, 14 figures. MNRAS accepted (submitted on November 10th, 2016)

Supermassive black holes launching plasma jets at close to speed of light, producing gamma-rays, have ubiquitously been found to be hosted by massive elliptical galaxies. Since elliptical galaxies are generally believed to be built through galaxy mergers, active galactic nuclei (AGN) launching relativistic jets are associated to the latest stages of galaxy evolution. We have discovered a pseudo-bulge morphology in the host galaxy of the gamma-ray AGN PKS 2004-447. This is the first gamma-ray emitter radio loud AGN found to be launched from a system where both black hole and host galaxy have been actively growing via secular processes. This is evidence for an alternative black hole-galaxy co-evolutionary path to develop powerful relativistic jets that is not merger-driven., Comment: 20 pages, 4 figures. Astrophysical Journal, accepted

We present deep Near-infrared (NIR) images of a sample of 19 intermediate-redshift ($0.310^{27}$ WHz$^{-1}$), previously classified as flat-spectrum radio quasars. We also compile host galaxy and nuclear magnitudes for blazars from literature. The combined sample (this work and compilation) contains 100 radio-loud AGN with host galaxy detections and a broad range of radio luminosities $L_{1.4GHz} \sim 10^{23.7} - 10^{28.3}$~WHz$^{-1}$, allowing us to divide our sample into high-luminosity blazars (HLBs) and low-luminosity blazars (LLBs). The host galaxies of our sample are bright and seem to follow the $\mu_{e}$-$R_{eff}$ relation for ellipticals and bulges. The two populations of blazars show different behaviours in the \mnuc - \mbulge plane, where a statistically significant correlation is observed for HLBs. Although it may be affected by selection effects, this correlation suggests a close coupling between the accretion mode of the central supermassive black hole and its host galaxy, that could be interpreted in terms of AGN feedback. Our findings are consistent with semi--analytical models where low--luminosity AGN emit the bulk of their energy in the form of radio jets, producing a strong feedback mechanism, and high--luminosity AGN are affected by galaxy mergers and interactions, which provide a common supply of cold gas to feed both nuclear activity and star formation episodes., Comment: Final version to appear in MNRAS

The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5 {\sigma} using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability time scale is estimated to be 6.4 +/- 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy., Comment: Corresponding Authors: J. Becerra (josefa.becerra@nasa.gov), M. Nievas Rosillo (mnievas@ucm.es), M. Manganaro (manganaro@iac.es), F. Tavecchio (fabrizio.tavecchio@brera.inaf.it) Published in The Astrophysical Journal Letters (ApJL), 2015ApJ...815L..23A, DOI: 10.1088/2041-8205/815/2/L23

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)