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511. 6Ms Chandra long-term analyses of AGNs
ID:
ivo://CDS.VizieR/J/ApJ/831/145
Title:
6Ms Chandra long-term analyses of AGNs
Short Name:
J/ApJ/831/145
Date:
21 Oct 2021
Publisher:
CDS
Description:
We perform long-term (~15 years, observed-frame) X-ray variability analyses of the 68 brightest radio-quiet active galactic nuclei (AGNs) in the 6Ms Chandra Deep Field-South survey; the majority are in the redshift range of 0.6-3.1, providing access to penetrating rest-frame X-rays up to ~10-30keV. Of the 68 sources, 24 are optical spectral type I AGNs, and the rest (44) are type II AGNs. The timescales probed in this work are among the longest for X-ray variability studies of distant AGNs. Photometric analyses reveal widespread photon flux variability: 90% of AGNs are variable above a 95% confidence level, including many X-ray obscured AGNs and several optically classified type II quasars. We characterize the intrinsic X-ray luminosity (L_X_) and absorption (N_H_) variability via spectral fitting. Most (74%) sources show L_X_ variability; the variability amplitudes are generally smaller for quasars. A Compton-thick candidate AGN shows variability of its high-energy X-ray flux, indicating the size of reflecting material to be <~0.3pc. L_X_ variability is also detected in a broad absorption line quasar. The N_H_ variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show N_H_ variability. One source transitions from an X-ray unobscured to obscured state, while its optical classification remains type I; this behavior indicates the X-ray eclipsing material is not large enough to obscure the whole broad-line region.
512. Multi-epoch VLBI survey of CJF sources
ID:
ivo://CDS.VizieR/J/A+A/484/119
Title:
Multi-epoch VLBI survey of CJF sources
Short Name:
J/A+A/484/119
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the second in a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-spectrum (hereafter CJF) sources and their analysis. We obtain a consistent motion dataset large enough to allow the systematic properties of the population to be studied. We present detailed kinematic analysis of the complete flux-density limited CJF survey. We computed 2-D kinematic models based on the optimal model-fitting parameters of multi-epoch VLBA observations. This allows us to calculate not only radial, but also orthogonal motions, and thus to study curvature and acceleration. Statistical tests of the motions measured and their reliability were performed. A correlation analysis between the derived apparent motions, luminosities, spectral indices, and core dominance and the resulting consequences is described. With at least one velocity in each of the 237 sources, this sample is much larger than any available before, so it allows a meaning ful statistical investigation of apparent motions and any possible correlations with other parameters in AGN jets. The main results to emerge are as follows: * In general motions are not consistent with a single uniform velocity applicable to all components along a jet. * We find a slight trend towards a positive outward acceleration and also adduce some evidence for greater acceleration in the innermost regions. * We find a lack of fast components at physical distances less than a few pc from the reference feature. * Only ~4% of the components from galaxies and <2% of those from quasars undergo large bends i.e. within 15{deg} of +/-90{deg}. * The distribution of radial velocities shows a broad distribution of velocities (apparent velocities up to 30c). Fifteen percent of the best-sampled jet components exhibit low velocities that may need to be explained in a different manner to the fast motions. * Some negative superluminal motions are seen, and in 15 cases (6%) these are definitely significant. * We find a strong correlation between the 5 GHz luminosity and the apparent velocity. * The CJF galaxies, on average, show slower apparent jet-component velocities than the quasars. * The mean velocity in the VLBA 2cm survey (Kellermann et al. 2004) is substantially higher than in the CJF survey, the ratio could be roughly a factor of 1.5-2. This supports the observed trend toward increasing apparent velocity with in creasing observing frequency. This AGN survey provides the basis for any statistical analysis of jet and jet-component properties.
513. Multi-wavelength analysis of CGRaBS blazars
ID:
ivo://CDS.VizieR/J/ApJ/851/33
Title:
Multi-wavelength analysis of CGRaBS blazars
Short Name:
J/ApJ/851/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a multi-frequency, time-averaged analysis of blazars included in the Candidate Gamma-ray Blazar Survey catalog. Our sample consists of 324 {gamma}-ray detected ({gamma}-ray loud) and 191 {gamma}-ray undetected ({gamma}-ray quiet) blazars; we consider all the data up to 2016 April 1. We find that both the {gamma}-ray loud and {gamma}-ray quiet blazar populations occupy similar regions in the WISE color-color diagram, and {gamma}-ray loud sources are brighter in the radio and X-ray bands. A simple one-zone synchrotron inverse-Compton emission model is applied to derive the physical properties of both populations. We find that the central black hole mass and accretion disk luminosity (L_disk_) computed from the modeling of the optical-UV emission with a Shakura-Sunyaev disk reasonably matches that estimated from the optical spectroscopic emission-line information. A significantly larger Doppler boosting in the {gamma}-ray loud blazars is noted, and their jets are more radiatively efficient. On the other hand, the {gamma}-ray quiet objects are more MeV-peaked and thus could be potential targets for next-generation MeV missions. Our results confirm earlier findings about the accretion-jet connection in blazars; however, many of the {gamma}-ray quiet blazars tend to deviate from the recent claim that the jet power exceeds L_disk_ in blazars. A broadband study, considering a larger set of {gamma}-ray quiet objects and also including BL Lacs, will be needed to confirm/reject this hypothesis as well as to verify the evolution of the powerful high-redshift blazars into their low-power nearby counterparts.
514. Multi-wavelength census of blazars
ID:
ivo://CDS.VizieR/J/A+A/641/A62
Title:
Multi-wavelength census of blazars
Short Name:
J/A+A/641/A62
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blazars are the rarest and most powerful active galactic nuclei, playing a crucial and growing role in today multi-frequency and multi-messenger astrophysics. They dominate the high-energy extragalactic sky and recently have been associated to high-energy astrophysical neutrinos, and they may be among the accelerators of the ultra-high energy cosmic rays. Current blazar catalogs, however, are incomplete and particularly depleted at low Galactic latitudes. We aim at augmenting the current blazar census starting from a sample of ALMA calibrators that provides more homogeneous sky coverage, especially at low Galactic latitudes, to build a catalog of blazar candidates that can provide candidate counterparts to unassociated gamma-ray sources and to sources of high-energy neutrino emission or ultra-high energy cosmic rays. Starting from the ALMA Calibrator Catalog we built a catalog of 1580 blazar candidates (ALMA Blazar Candidates) for which we collect multi-wavelength information, including Gaia photometric, parallax and proper motion data, SDSS and LAMOST photometric and spectral data, WISE photometric data, X-ray (Swift-XRT, Chandra-ACIS and XMM-Newton-EPIC) count-rates and spectra, and Fermi-LAT fluxes and spectral slopes. We also compared our ALMA Blazar Candidates with existing blazar catalogs, like 4FGL, 3HSP, WIBRaLS2 and the KDEBLLACS. The ALMA Blazar Candidates catalogue fills the lack of low Galactic latitude sources in current blazar catalogues. Cross-matching this catalog with Gaia DR2, SDSS DR12, LAMOST DR5, AllWISE and 4FGL catalogues we obtained 805, 295, 31, 1311 and 259 matches, respectively. ALMA Blazar Candidates are significantly dimmer than known blazars in Gaia g band, while the difference in the Gaia b-r colour between the two populations is less pronounced. Also, ALMA Blazar Candidates sources appear bluer in SDSS than known blazars, although with low statistical significance. Most ALMA Blazar Candidates classified as QSO and BL Lac fall into the SDSS colour regions of low redshift quasars, with some QSOs entering the regions of higher redshift quasars. We collected 110 optical spectra in SDSS DR12 and LAMOST DR5, which mostly classify the corresponding sources as QSO (98), while 12 sources resulted galactic objects. Regarding WISE colours, we found that ABC sources are significantly bluer than known blazars in the w2-w3 and w3-w4 colours. In X-rays we detected 173 ALMA Blazar Candidates, and we were able to extract a X-ray spectra for 92 of them. Our sources are on average similar in X-rays to known blazar in terms of count-rates and spectral slopes, implying that our sample is covering the same region of the blazar parameter space in this band. A comparison of gamma-ray properties shown that ALMA Blazar Candidates are on average dimmer, and their gamma-ray spectra are softer than known blazars, indicating a significant contribution of FSRQ sources. Making use of WISE colours, we classified 715 ALMA Blazar Candidates as candidate gamma-ray blazar of different classes. We built a new catalogue of 1580 candidate blazars with a rich multi-wavelength data-set, filling the lack of low Galactic latitude sources in current blazar catalogues. This will be particularly important to identify the source population of high energy neutrinos or ultra-high energy cosmic rays, or to verify the Gaia optical reference frame. In addition, ALMA Blazar Candidates can be investigated both through optical spectroscopic observation campaigns or through repeated photometric observations for variability studies. In this context, the data collected by the upcoming LSST surveys will provide a key tool to investigate the possible blazar nature of these sources.
515. Multiwavelength observations of Mrk 501 in 2008
ID:
ivo://CDS.VizieR/J/A+A/573/A50
Title:
Multiwavelength observations of Mrk 501 in 2008
Short Name:
J/A+A/573/A50
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the {gamma}-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available {gamma}-ray instrumentation was easier to perform. 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 telescopesMAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign.
516. Multiwavelength obs. of BL Lac in 2012-2013
ID:
ivo://CDS.VizieR/J/ApJ/816/53
Title:
Multiwavelength obs. of BL Lac in 2012-2013
Short Name:
J/ApJ/816/53
Date:
21 Oct 2021
Publisher:
CDS
Description:
BL Lac, the eponymous blazar, flared to historically high levels at millimeter, infrared, X-ray, and gamma-ray wavelengths in 2012. We present observations made with Herschel, Swift, NuSTAR, Fermi, the Submillimeter Array, CARMA, and the VLBA in 2012-2013, including three months with nearly daily sampling at several wavebands. We have also conducted an intensive campaign of 30 hr with every-orbit observations by Swift and NuSTAR, accompanied by Herschel, and Fermi observations. The source was highly variable at all bands. Time lags, correlations between bands, and the changing shapes of the spectral energy distributions can be explained by synchrotron radiation and inverse Compton emission from nonthermal seed photons originating from within the jet. The passage of four new superluminal very long baseline interferometry knots through the core and two stationary knots about 4 pc downstream accompanied the high flaring in 2012-2013. The seed photons for inverse Compton scattering may arise from the stationary knots and from a Mach disk near the core where relatively slow-moving plasma generates intense nonthermal radiation. The 95 spectral energy distributions obtained on consecutive days form the most densely sampled, broad wavelength coverage for any blazar. The observed spectral energy distributions and multi-waveband light curves are similar to simulated spectral energy distributions and light curves generated with a model in which turbulent plasma crosses a conical shock with a Mach disk.
517. Multiwavelength survey of AGNs
ID:
ivo://CDS.VizieR/J/MNRAS/425/1215
Title:
Multiwavelength survey of AGNs
Short Name:
J/MNRAS/425/1215
Date:
21 Oct 2021
Publisher:
CDS
Description:
We aim to study the effect of environment on the presence and fuelling of active galactic nuclei (AGNs) in massive galaxy clusters. We explore the use of different AGN detection techniques with the goal of selecting AGN across a broad range of luminosities, AGN/host galaxy flux ratios and obscuration levels. From a sample of 12 galaxy clusters at redshifts 0.5<z<0.9, we identify AGN candidates using optical variability from multi-epoch Hubble Space Telescope imaging, X-ray point sources in Chandra images and mid-infrared (IR) spectral energy distribution power-law fits through the Spitzer Infrared Array Camera channels. We find 178 optical variables, 74 X-ray point sources and 64 IR power-law sources, resulting in an average of ~25 AGN per cluster.
518. MURALES survey. I. 3C 459 data cube.
ID:
ivo://CDS.VizieR/J/A+A/619/A83
Title:
MURALES survey. I. 3C 459 data cube.
Short Name:
J/A+A/619/A83
Date:
21 Oct 2021
Publisher:
CDS
Description:
We observed the FR II radio galaxy 3C 459 (z=0.22) with the MUSE spectrograph at the Very Large Telescope (VLT) as part of the MURALES project (a MUse RAdio Loud Emission line Snapshot survey). We detected diffuse nuclear emission and a filamentary ionized gas structure forming a one-sided, triangular-shaped region extending out to ~80kpc. The central emission line region is dominated by two compact knots of similar flux: the first (N1) cospatial with the radio core and the (N2) second located 1.2" (5.3kpc) to the SE. The two regions differ dramatically from the point of view of velocity (with an offset of ~400km/s), line widths, and line ratios. This suggests that we are observing a dual AGN system formed by a radio loud AGN and type 2 QSO companion, which is the result of the recent merger that also produced its disturbed host morphology. The alternative possibility that N2 is just a bright emission line knot resulting from, for example, a jet-cloud interaction, is disfavored because of 1) the presence of a high ionization bicone whose apex is located at N2; 2) the observed narrow line widths; 3) its line luminosity (~10^42^erg/s) typical of luminous QSOs; and 4) its location, which is offset from the jet path. The putative secondary AGN must be highly obscured, since we do not detect any emission in the Chandra and infrared Hubble Space Telescope images.
519. Naked active galactic nuclei
ID:
ivo://CDS.VizieR/J/A+A/424/519
Title:
Naked active galactic nuclei
Short Name:
J/A+A/424/519
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we report the discovery of a new class of active galactic nucleus in which although the nucleus is viewed directly, no broad emission lines are present. The results are based on a survey for AGN in which a sample of about 800 quasars and emission line galaxies were monitored yearly for 25 years. Among the emission line galaxies was the expected population of Seyfert 2 galaxies with only narrow forbidden lines in emission, and no broad lines. However, from the long term monitoring programme it was clear that some 10% of these were strongly variable with strong continuum emission. It is argued that these objects can only be Seyfert 1 galaxies in which the nucleus is viewed directly, but in which broad emission lines are completely absent. We compare these observations with other cases from the literature where the broad line region is reported to be weak or variable, and investigate the possibility that the absence of the broad line component is due to reddening. We conclude that this does not account for the observations, and that in these AGN the broad line region is absent. We also tentatively identify more luminous quasars from our sample where the broad emission lines also appear to be absent. The consequences of this for AGN models are discussed, and a case is made that we are seeing AGN in a transition stage between the fuel supply from a surrounding star cluster being cut off, and the nucleus becoming dormant.
520. Narrow-band imaging of 6 Seyfert-2 galaxies
ID:
ivo://CDS.VizieR/J/A+A/456/953
Title:
Narrow-band imaging of 6 Seyfert-2 galaxies
Short Name:
J/A+A/456/953
Date:
21 Oct 2021
Publisher:
CDS
Description:
While [OIII] narrow-band imaging is commonly used to measure the size of the narrow-line regions (NLRs) in active galactic nuclei (AGNs), it can be contaminated by emission from surrounding starbursts. Recently, we have shown that long-slit spectroscopy provides a valuable alternative approach to probe the size in terms of AGN photoionisation. Moreover, several parameters of the NLR can be directly accessed. We here apply the same methods developed and described for the Seyfert-2 galaxy NGC1386 to study the NLR of five other Seyfert-2 galaxies by using high-sensitivity spatially-resolved optical spectroscopy obtained at the VLT and the NTT. We probe the AGN-photoionisation of the NLR and thus, its "real" size using diagnostic line-ratio diagrams. We derive physical properties of the NLR such as reddening, ionisation parameter, electron density, and velocity as a function of distance from the nucleus. For NGC5643, the diagnostic diagrams unveil a similar transition between line ratios falling in the AGN regime and those typical for HII regions as found for NGC1386, thus determining the size of the NLR. For the other four objects, all measured line ratios fall in the AGN regime. In almost all cases, both electron density and ionisation parameter decrease with radius. Deviations from this general behaviour (such as a secondary peak) seen in both the ionisation parameter and electron density can be interpreted as signs of shocks from the interaction of a radio jet and the NLR gas. In several objects, the gaseous velocity distribution is characteristic for rotational motion in an (inclined) emission-line disk in the centre. We compare our results to those of NGC1386 and show that the latter can be considered as prototypical also for this larger sample. We discuss our findings in detail for each object.