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Start Over Subject quasars Validation Level 2
1061. X-ray polarization predictions in blazars
ID:
ivo://CDS.VizieR/J/ApJ/880/29
Title:
X-ray polarization predictions in blazars
Short Name:
J/ApJ/880/29
Date:
21 Oct 2021
Publisher:
CDS
Description:
X-ray polarization should provide new probes of magnetic field geometry and acceleration physics near the base of blazar jets, but near-future missions will have limited sensitivity. We thus use existing lower energy data and X-ray variability measurements in the context of a basic synchro-Compton model to predict the X-ray polarization level and the probability of detection success for individual sources, listing the most attractive candidates for an Imaging X-ray Polarimetry Explorer campaign. We find that, as expected, several high-peak blazars such as Mrk 421 can be easily measured in 100ks exposures. Most low-peak sources should only be accessible to triggered campaigns during bright flares. Surprisingly, a few intermediate peak sources can have anomalously high X-ray polarization and thus are attractive targets.
1062. X-ray properties of 26 high-luminosity quasars
ID:
ivo://CDS.VizieR/J/MNRAS/504/5556
Title:
X-ray properties of 26 high-luminosity quasars
Short Name:
J/MNRAS/504/5556
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an investigation of the interdependence of the optical-to-X-ray spectral slope (aox), the HeII equivalent-width (EW), and the monochromatic luminosity at 2500{AA} (L2500). The values of {alpha}_ox_ and HeII EW are indicators of the strength/shape of the quasar ionizing continuum, from the ultraviolet (UV; 1500-2500{AA}), through the extreme ultraviolet (EUV;300-50{AA}), to the X-ray (2keV) regime. For this investigation, we measure the HeII EW of 206 radio-quiet quasars devoid of broad absorption lines that have high-quality spectral observations of the UV and 2keV X-rays. The sample spans wide redshift (z~0.13-3.5) and luminosity (logL_2500_~29.2-32.5erg/s/Hz) ranges. We recover the well-known {alpha}_ox_-L_2500_ and HeII EW-L_2500_ anti-correlations, and we find a similarly strong correlation between {alpha}_ox_ and HeII EW, and thus the overall spectral shape from the UV, through the EUV, to the X-ray regime is largely set by luminosity. A significant {alpha}_ox_-HeII EW correlation remains after removing the contribution of L_2500_ from each quantity, and thus the emission in the EUV and the X-rays are also directly tied. This set of relations is surprising, since the UV, EUV, and X-ray emission are expected to be formed in three physically distinct regions. Our results indicate the presence of a redshift-independent physical mechanism that couples the continuum emission from these three different regions, and thus controls the overall continuum shape from the UV to the X-ray regime.
1063. X-ray properties of PHL1811 analogs and WLQs
ID:
ivo://CDS.VizieR/J/ApJ/805/122
Title:
X-ray properties of PHL1811 analogs and WLQs
Short Name:
J/ApJ/805/122
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL1811, at z~0.5-2.9. New Chandra 1.5-9.5ks exploratory observations were obtained for 32 objects while the others have archival X-ray observations. Significant fractions of these luminous type 1 quasars are distinctly X-ray weak compared to typical quasars, including 16 (48%) of the WLQs and 17 (94%) of the PHL 1811 analogs with average X-ray weakness factors of 17 and 39, respectively. We measure a relatively hard ({Gamma}=1.16^+0.37^_-0.32_) effective power-law photon index for a stack of the X-ray weak subsample, suggesting X-ray absorption, and spectral analysis of one PHL 1811 analog, J1521+5202, also indicates significant intrinsic X-ray absorption. We compare composite Sloan Digital Sky Survey spectra for the X-ray weak and X-ray normal populations and find several optical-UV tracers of X-ray weakness, e.g., FeII rest-frame equivalent width (REW) and relative color. We describe how orientation effects under our previously proposed "shielding-gas" scenario can likely unify the X-ray weak and X-ray normal populations. We suggest that the shielding gas may naturally be understood as a geometrically thick inner accretion disk that shields the broad line region from the ionizing continuum. If WLQs and PHL 1811 analogs have very high Eddington ratios, the inner disk could be significantly puffed up (e.g., a slim disk). Shielding of the broad emission-line region by a geometrically thick disk may have a significant role in setting the broad distributions of CIV REW and blueshift for quasars more generally.
1064. X-ray selected ROSAT AGN spectra
ID:
ivo://CDS.VizieR/J/A+A/350/805
Title:
X-ray selected ROSAT AGN spectra
Short Name:
J/A+A/350/805
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the emission line properties of a sample of 76 bright soft X-ray selected ROSAT Active Galactic Nuclei. All optical counterparts are Seyfert 1 galaxies with rather narrow permitted lines, strong optical FeII line blends, and weak forbidden lines. By selection, they also have steep soft X-ray spectra when compared with typical Seyfert 1 galaxies. We discuss possible origins of these peculiar trends employing detailed correlation analyses, including a Principal Component Analysis. The optical spectra are presented in the Appendix.
1065. X-rays from large optical QSO sample
ID:
ivo://CDS.VizieR/J/ApJ/450/51
Title:
X-rays from large optical QSO sample
Short Name:
J/ApJ/450/51
Date:
21 Oct 2021
Publisher:
CDS
Description:
Of the more than 1000 QSOs in the Large Bright Quasar Survey (LBQS), we study the X-ray properties of 908 that were covered by the ROSAT All-Sky Survey (RASS). These data constitute among the largest, most homogeneous X-ray surveys of QSOs to date, and as such are well suited to the study of the multiwavelength properties of QSOs. Due to the ~600 s RASS exposure times, only 10% of the QSOs are detected in X-rays. However, by stacking X-ray counts, we obtain effectively much more sensitive observations for an average QSO in bins of redshift or luminosity, and for several classes of QSOs. We confirm a correlation of alpha_ox (slope of a hypothetical power law connecting 2500A and 2keV) with luminosity for the overall sample. For higher redshifts and optical luminosities, radio-loud QSOs appear to become progressively more luminous in X-rays than radio-quiet QSOs. The X-ray properties of a subsample of 36 broad absorption line QSOs suggest that they are strongly absorbed or underluminous in the X-rays, while a subsample of 22 Fe II-strong QSOs is anomalously X-ray bright.
1066. X-ray spectral analysis of AGNs
ID:
ivo://CDS.VizieR/J/MNRAS/443/1999
Title:
X-ray spectral analysis of AGNs
Short Name:
J/MNRAS/443/1999
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results from an X-ray spectral analysis of active galactic nuclei (AGN) in the Chandra Deep Field-South, All-wavelength Extended Groth-strip International Survey (AEGIS)-Deep X-ray survey (XD) and Chandra-Cosmic Evolution Surveys (COSMOS), focusing on the identification and characterization of the most heavily obscured, Compton thick (CT, NH>10^24^cm^-2^) sources. Our sample is comprised of 3184 X-ray selected extragalactic sources, which has a high rate of redshift completeness (96.6 per cent), and includes additional spectroscopic redshifts and improved photometric redshifts over previous studies. We use spectral models designed for heavily obscured AGN which self-consistently include all major spectral signatures of heavy absorption. We validate our spectral fitting method through simulations, identify CT sources not selected through this method using X-ray colours and take considerations for the constraints on NH given the low count nature of many of our sources. After these considerations, we identify a total of 100 CT AGN with best-fitting NH >10^24^cm^-2^ and NH constrained to be above 10^23.5^cm^-2^ at 90 per cent confidence. These sources cover an intrinsic 2-10keV X-ray luminosity range of 10^42^-3x10^45^erg/s and a redshift range of z=0.1-4. This sample will enable characterization of these heavily obscured AGN across cosmic time and to ascertain their cosmological significance. These survey fields are sites of extensive multiwavelength coverage, including near-infrared Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) data and far-infrared Herschel data, enabling forthcoming investigations into the host properties of CT AGN. Furthermore, by using the torus models to test different covering factor scenarios, and by investigating the inclusion of the soft scattered emission, we find evidence that the covering factor of the obscuring material decreases with LX for all redshifts, consistent with the receding torus model, and that this factor increases with redshift, consistent with an increase in the obscured fraction towards higher redshifts. The strong relationship between the parameters of obscuration and LX points towards an origin intrinsic to the AGN; however, the increase of the covering factor with redshift may point towards contributions to the obscuration by the host galaxy. We make NH, {GAMMA} (with uncertainties), observed X-ray fluxes and intrinsic 2-10keV luminosities for all sources analysed in this work publicly available in an online catalogue.
1067. X-ray spectrum of 1H0419-577
ID:
ivo://CDS.VizieR/J/A+A/556/A94
Title:
X-ray spectrum of 1H0419-577
Short Name:
J/A+A/556/A94
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we analyze the X-ray, UV and optical data of the Seyfert 1.5 galaxy 1H0419-577, with the aim of detecting and studying an ionized-gas outflow. The source was observed simultaneously in the X-rays with XMM-Newton and in the UV with HST-COS. Optical data were also acquired with the XMM-Newton Optical Monitor. We detected a thin, lowly ionized warm absorber (logxi~0.03, logNH~19.9cm^-2^) in the X-ray spectrum, consistent to be produced by the same outflow already detected in the UV. Provided the gas density estimated in the UV, the outflow is consistent to be located in the host galaxy, at ~kpc scale. Narrow emission lines were detected in the X-rays, in the UV and also in the optical spectrum. A single photoionized-gas model cannot account for all the narrow lines emission, indicating that the narrow line region is probably a stratified environment, differing in density and ionization. X-ray lines are unambiguously produced in a more highly ionized gas phase than the one emitting the UV lines. The analysis suggests also that the X-ray emitter may be just a deeper portion of the same gas layer producing the UV lines. Optical lines are probably produced in another, disconnected gas system. The different ionization condition, and the ~pc scale location suggested by the line width for the narrow lines emitters, argue against a connection between the warm absorber and the narrow line region in this source.
1068. X-ray survey of the 2Jy sample. I.
ID:
ivo://CDS.VizieR/J/MNRAS/440/269
Title:
X-ray survey of the 2Jy sample. I.
Short Name:
J/MNRAS/440/269
Date:
21 Oct 2021
Publisher:
CDS
Description:
We carry out a systematic study of the X-ray emission from the active nuclei of the 0.02<z<0.7 2Jy sample, using Chandra and XMM-Newton observations. We combine our results with those from mid-infrared, optical emission-line and radio observations, and add them to those of the 3CRR sources. We show that the low-excitation objects in our samples show signs of radiatively inefficient accretion. We study the effect of the jet-related emission on the various luminosities, confirming that it is the main source of soft X-ray emission for our sources. We also find strong correlations between the accretion-related luminosities, and identify several sources whose optical classification is incompatible with their accretion properties. We derive the bolometric and jet kinetic luminosities for the samples and find a difference in the total Eddington rate between the low- and high-excitation populations, with the former peaking at ~1% and the latter at ~20% Eddington. Our results are consistent with a simple Eddington switch when the effects of environment on radio luminosity and black hole mass calculations are considered. The apparent independence of jet kinetic power and radiative luminosity in the high-excitation population in our plots supports a model in which jet production and radiatively efficient accretion are not strongly correlated in high-excitation objects, though they have a common underlying mechanism.
1069. X-ray/UV ratio of AGN
ID:
ivo://CDS.VizieR/J/A+A/619/A95
Title:
X-ray/UV ratio of AGN
Short Name:
J/A+A/619/A95
Date:
21 Oct 2021
Publisher:
CDS
Description:
The well established negative correlation between the {alpha}_OX_ spectral slope and the optical/UV luminosity, a by product of the relation between X-rays and optical/UV luminosity, is affected by a relatively large dispersion. The main contributions can be variability in the X-ray/UV ratio and/or changes in fundamental physical parameters. We want to quantify the contribution of variability within single sources (intra-source dispersion) and that due to variations of other quantities different from source to source (inter-source dispersion). We use archival data from the XMM-Newton Serendipitous Source Catalog (XMMSSC, Cat. IX/50) and from the XMM-OM Serendipitous Ultra-violet Source Survey (XMMOM-SUSS3, Cat. II/340). We select a sub-sample in order to decrease the dispersion of the relation due to the presence of Radio-Loud and Broad Absorption Line objects, and to absorptions in both X-ray and optical/UV bands. We use the Structure Function (SF) to estimate the contribution of variability to the dispersion. We analyse the dependence of the residuals of the relation on various physical parameters in order to characterise the inter-source dispersion. We find a total dispersion of {sigma}~0.12 and we find that intrinsic variability contributes for 56 percent of the variance of the {alpha}_OX_-L_UV_ relation. If we select only sources with a larger number of observational epochs (>2) the dispersion of the relation decreases by approximately 15 percent. We find weak but significant dependences of the residuals of the relation on black-hole mass and on Eddington ratio, which are also confirmed by a multivariate regression analysis of {alpha}_OX_ as a function of UV luminosity and black-hole mass and/or Eddington ratio. We find a weak positive correlation of both the {alpha}_OX_ index and the residuals of the {alpha}_OX_-LUV relation with inclination indicators, such as the FWHM(H{beta}) and the EW[OIII], suggesting a weak increase of X-ray/UV ratio with the viewing angle. This suggests the development of new viewing angle indicators possibly applicable at higher redshifts. Moreover, our results suggest the possibility of selecting a sample of objects, based on their viewing angle and/or black-hole mass and Eddington ratio, for which the {alpha}_OX_-LUV relation is as tight as possible, in light of the use of the optical/UV-X-ray luminosity relation to build a distance modulus (DM)-z plane and estimate cosmological parameters.
1070. X-ray/UV ratio of 2XMM AGN
ID:
ivo://CDS.VizieR/J/A+A/519/A17
Title:
X-ray/UV ratio of 2XMM AGN
Short Name:
J/A+A/519/A17
Date:
21 Oct 2021
Publisher:
CDS
Description:
The observed relation between the X-ray radiation from active galactic nuclei, originating in the corona, and the optical/UV radiation from the disk is usually described by the anticorrelation between the UV to X-ray slope {alpha}_ox_ and the UV luminosity. Many factors can affect this relation, including: i) enhanced X-ray emission associated with the jets of radio-loud AGNs, ii) X-ray absorption associated with the UV broad absorption line (BAL) outflows, iii) other X-ray absorption not associated with BALs, iv) intrinsic X-ray weakness, v) UV and X-ray variability, and non-simultaneity of UV and X-ray observations. The separation of these effects provides information about the intrinsic {alpha}_ox_-L_UV_ relation and its dispersion, constraining models of disk-corona coupling. We use simultaneous UV/X-ray observations to remove the influence of non-simultaneous measurements from the {alpha}_ox_-L_UV_ relation.