Search

Start Over Subject active galactic nuclei Capability Type Simple Cone Search
901. X-ray flux variability of AGN
ID:
ivo://CDS.VizieR/J/MNRAS/466/3309
Title:
X-ray flux variability of AGN
Short Name:
J/MNRAS/466/3309
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of a systematic study of flux variability on hourly time-scales in a large sample of active galactic nuclei (AGN) in the 3-79keV band using data from Nuclear Spectroscopic Telescope Array. Our sample consists of four BL Lac objects (BL Lacs), three flat spectrum radio quasars (FSRQs) 24 Seyfert 1, 42 Seyfert 2 and eight narrow line Seyfert 1 (NLSy1) galaxies. We find that in the 3-79keV band, about 65 per cent of the sources in our sample show significant variations on hourly time-scales. Using the Mann-Whitney U-test and the Kolmogorov-Smirnov test, we find no difference in the variability behaviour between Seyfert 1 and 2 galaxies. The blazar sources (FSRQs and BL Lacs) in our sample are more variable than Seyfert galaxies that include Seyfert 1 and Seyfert 2 in the soft (3-10keV), hard (10-79keV) and total (3-79keV) bands. NLSy1 galaxies show the highest duty cycle of variability (87 per cent), followed by BL Lacs (82 per cent), Seyfert galaxies (56 per cent) and FSRQs (23 per cent). We obtained flux doubling/halving time in the hard X-ray band less than 10 min in 11 sources. The flux variations between the hard and soft bands in all the sources in our sample are consistent with zero lag.
902. X-ray measurements of ChaMP-SDSS galaxies
ID:
ivo://CDS.VizieR/J/ApJ/705/1336
Title:
X-ray measurements of ChaMP-SDSS galaxies
Short Name:
J/ApJ/705/1336
Date:
21 Oct 2021
Publisher:
CDS
Description:
The combination of the Sloan Digital Sky Survey (SDSS) and the Chandra Multiwavelength Project (ChaMP; Green et al. 2004ApJS..150...43G) currently offers the largest and most homogeneously selected sample of nearby galaxies for investigating the relation between X-ray nuclear emission, nebular line emission, black hole masses, and properties of the associated stellar populations. We provide X-ray spectral fits and valid uncertainties for all the galaxies with counts ranging from 2 to 1325 (mean 76, median 19). We present here novel constraints that both X-ray luminosity L_X_ and X-ray spectral energy distribution bring to the galaxy evolutionary sequence HII->Seyfert/Transition Object->LINER->Passive suggested by optical data.
903. X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
ID:
ivo://CDS.VizieR/J/ApJ/876/50
Title:
X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
Short Name:
J/ApJ/876/50
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of a Sloan Digital Sky Survey IV eBOSS program to target X-ray sources and mid-infrared-selected Wide-field Infrared Survey Explorer (WISE) active galactic nucleus (AGN) candidates in a 36.8deg^2^ region of Stripe 82. About half this survey (15.6deg^2^) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGNs in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to r~22. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGNs, with a median sample redshift of z~1. About 30% of the AGNs are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGNs at z<0.5 have emission line ratios consistent with star-forming galaxies, so whether they are buried AGNs or star-forming galaxy contaminants is currently unclear. We find that 61% of X-ray AGNs are not selected as mid-infrared AGNs, with 22% of X-ray AGNs undetected by WISE. Most of these latter AGNs have high X-ray luminosities (Lx>10^44^erg/s), indicating that mid-infrared selection misses a sizable fraction of the highest luminosity AGNs, as well as lower luminosity sources where AGN-heated dust is not dominating the mid-infrared emission. Conversely, ~58% of WISE AGNs are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray-detected WISE AGNs.
904. X-ray & MIR luminosities of the GBT galaxies
ID:
ivo://CDS.VizieR/J/ApJ/892/18
Title:
X-ray & MIR luminosities of the GBT galaxies
Short Name:
J/ApJ/892/18
Date:
19 Jan 2022 08:55:44
Publisher:
CDS
Description:
We present an investigation of the dependence of H_2_O maser detection rates and properties on the mid-IR active galactic nucleus (AGN) luminosity, L_AGN_, and the obscuring column density, N_H_, based on mid-IR and hard X-ray photometry. Based on spectral energy distribution fitting that allows for decomposition of the black hole accretion and star formation components in the mid-infrared, we show that the megamaser (disk maser) detection rate increases sharply for galaxies with 12{mu}m AGN luminosity L_12um_^AGN^ greater than 10^42^erg/s, from <~3% (<~2%) to ~12% (~5%). By using the ratio of the observed X-ray to mid-IR AGN luminosity as an indicator of N_H_, we also find that megamaser (disk maser) detection rates are boosted to 15% (7%) and 20% (9%) for galaxies with N_H_>=10^23^/cm^2^ and N_H_>=10^24^cm^-2^, respectively. Combining these column density cuts with a constraint for high L_12um_^AGN^ (>=10^42^erg/s) predicts further increases in the megamaser (disk maser) detection rates to 19% (8%) and 27% (14%), revealing unprecedented potential increases of the megamaser and disk maser detection rates by a factor of 7-15 relative to the current rates, depending on the chosen sample selection criteria. A noteworthy aspect of these new predictions is that the completeness rates are only compromised mildly, with the rates remaining at the level of ~95% (~50%) for sources with N_H_>=10^23^/cm^2^ (N_H_>=10^24^/cm^2^). Applying these selection methods to current X-ray AGN surveys predicts the detection of >~15 new megamaser disks.
905. X-ray observations of Stripe 82
ID:
ivo://CDS.VizieR/J/MNRAS/436/3581
Title:
X-ray observations of Stripe 82
Short Name:
J/MNRAS/436/3581
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have analysed the XMM-Newton and Chandra data overlapping ~16.5deg^2^ of Sloan Digital Sky Survey Stripe 82, including ~4.6deg^2^ of proprietary XMM-Newton data that we present here. In total, 3362 unique X-ray sources are detected at high significance. We derive the XMM-Newton number counts and compare them with our previously reported Chandra logN-logS relations and other X-ray surveys. The Stripe 82 X-ray source lists have been matched to multiwavelength catalogues using a maximum likelihood estimator algorithm. We discovered the highest redshift (z=5.86) quasar yet identified in an X-ray survey. We find 2.5 times more high-luminosity (L_X_>10^45erg/s) AGN than the smaller area Chandra and XMM-Newton survey of COSMOS and 1.3 times as many identified by XBootes. Comparing the high-luminosity active galactic nuclei (AGN) we have identified with those predicted by population synthesis models, our results suggest that this AGN population is a more important component of cosmic black hole growth than previously appreciated. Approximately a third of the X-ray sources not detected in the optical are identified in the infrared, making them candidates for the elusive population of obscured high-luminosity AGN in the early universe.
906. X-ray Observations of Stripe 82
ID:
ivo://CDS.VizieR/J/ApJ/817/172
Title:
X-ray Observations of Stripe 82
Short Name:
J/ApJ/817/172
Date:
21 Oct 2021
Publisher:
CDS
Description:
We release the next installment of the Stripe 82 X-ray survey point-source catalog, which currently covers 31.3deg^2^ of the Sloan Digital Sky Survey (SDSS) Stripe 82 Legacy field. In total, 6181 unique X-ray sources are significantly detected with XMM-Newton (>5{sigma}) and Chandra (>4.5{sigma}). This catalog release includes data from XMM-Newton cycle AO 13, which approximately doubled the Stripe 82X survey area. The flux limits of the Stripe 82X survey are 8.7x10^-16^erg/s/cm2, 4.7x10^-15^erg/s/cm2, and 2.1x10^-15^erg/s/cm2 in the soft (0.5-2keV), hard (2-10keV), and full bands (0.5-10keV), respectively, with approximate half-area survey flux limits of 5.4x10^-15^erg/s/cm2, 2.9x10^-14^erg/s/cm2, and 1.7x10^-14^erg/s/cm2. We matched the X-ray source lists to available multi-wavelength catalogs, including updated matches to the previous release of the Stripe 82X survey; 88% of the sample is matched to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich ancillary multi-wavelength data, including coadded SDSS photometry, mid-infrared WISE coverage, near-infrared coverage from UKIDSS and VISTA Hemisphere Survey, ultraviolet coverage from GALEX, radio coverage from FIRST, and far-infrared coverage from Herschel, as well as existing ~30% optical spectroscopic completeness, we are beginning to uncover rare objects, such as obscured high-luminosity active galactic nuclei at high-redshift. The Stripe 82X point source catalog is a valuable data set for constraining how this population grows and evolves, as well as for studying how they interact with the galaxies in which they live.
907. X-ray of active galaxies and nuclei
ID:
ivo://CDS.VizieR/VII/181
Title:
X-ray of active galaxies and nuclei
Short Name:
VII/181
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)
908. X-ray properties of AGN from the CJF sample
ID:
ivo://CDS.VizieR/J/A+A/476/759
Title:
X-ray properties of AGN from the CJF sample
Short Name:
J/A+A/476/759
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the soft X-ray properties obtained in the ROSAT All-Sky survey and from pointed PSPC observations for the AGN in the complete flux-density limited Caltech-Jodrell Bank flat spectrum sample (hereafter CJF). CJF is a VLBI survey (VLBA observations at 5GHz) of 293 AGN with detailed information on jet component motion. We investigate and discuss the soft X-ray properties of this AGN sample and examine the correlations between X-ray and VLBI properties, test beaming scenarios, and search for the discriminating properties between the sub-samples detected and not detected by ROSAT. Comparing the observed and the predicted X-ray fluxes by assuming an Inverse Compton (IC) origin for the observed X-rays, we compute the beaming or Doppler factor, {delta}_IC_, for the CJF sources and compare it with the equipartition Doppler factor, {delta}_EQ_. We further contrast the Doppler factors with other beaming indicators derived from the VLBI observations, such as the value of the expansion velocity, and the observed and intrinsic brightness temperature. We calculate two different core dominance parameters (R): the ratio of total VLBI flux to single-dish flux, R_V_, and the ratio of the VLBI core-component flux to single-dish flux, R_C_. In addition, we investigate the large-scale radio structure of the AGN and the difference between the pc- and kpc-scale structure (misalignment) with regard to the X-ray observations.
909. X-ray properties of AGN in CDFS
ID:
ivo://CDS.VizieR/J/A+A/451/457
Title:
X-ray properties of AGN in CDFS
Short Name:
J/A+A/451/457
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed X-ray spectral analysis of the sources in the 1Ms catalog of the Chandra Deep Field South (CDFS, J/ApJS/139/369) taking advantage of optical spectroscopy and photometric redshifts for 321 extragalactic sources out of the total sample of 347 sources. As a default spectral model, we adopt a power law with slope Gamma with an intrinsic redshifted absorption N_H_, a fixed Galactic absorption and an unresolved Fe emission line. For 82 X-ray bright sources, we are able to perform the X-ray spectral analysis leaving both Gamma and N_H_ free.
910. X-ray properties of AGNs in XBS
ID:
ivo://CDS.VizieR/J/A+A/530/A42
Title:
X-ray properties of AGNs in XBS
Short Name:
J/A+A/530/A42
Date:
21 Oct 2021
Publisher:
CDS
Description:
X-ray surveys are a key instrument in the study of active galactic nuclei (AGN). Thanks to their penetrating ability, X-rays are able to map the innermost regions close to the central super massive black hole (SMBH) as well as to detect and characterize its emission up to high redshift. We present here a detailed X-ray spectral analysis of the AGN belonging to the XMM-Newton bright survey (XBS). The XBS is composed of two flux-limited samples selected in the complementary 0.5-4.5 and 4.5-7.5keV energy bands and comprising more than 300 AGN up to redshift ~2.4. We performed an X-ray analysis following two different approaches: by analyzing individually each AGN X-ray spectrum and by constructing average spectra for different AGN types.