<i>Chandra</i>Observations of Red Sloan Digital Sky Survey Quasars

Gallagher, S. C.; Richards, Gordon T.; Alexander, D. M.; Anderson, Scott F.; Bauer, F. E.; Brandt, W. N.; Schneider, Donald P.

doi:10.1086/507842

Cited by 20 publications

(12 citation statements)

References 63 publications

(119 reference statements)

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“…The higher value found for dust in the lens is broadly consistent with measurements for other lens systems (Dai & Kochanek 2009), while the value for dust at the source redshift is much lower than expected from this observed correlation. However, such low dust-to-gas ratios appear to be common for intrinsic absorption features of quasars caused by quasar outflow (Hall et al 2006), which can be explained by dust evaporation due to irradiation by the central source. Thus, we cannot draw any firm conclusion about the origin of the absorption from this analysis.…”

Section: Comparison With Optical and Radio Flux Ratiosmentioning

confidence: 99%

THECHANDRAVIEW OF THE LARGEST QUASAR LENS SDSS J1029+2623

Ota

Oguri

Dai

et al. 2012

ApJ

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We present results from Chandra observations of the cluster lens SDSS J1029+2623 at z l = 0.58, which is a gravitationally lensed quasar with the largest known image separation. We clearly detect X-ray emission both from the lensing cluster and the three lensed quasar images. The cluster has an X-ray temperature of kT = 8.1 +2.0 −1.2 keV and bolometric luminosity of L X = 9.6 × 10 44 erg s −1 . Its surface brightness is centered near one of the brightest cluster galaxies, and it is elongated east-west. We identify a subpeak northwest of the main peak, which is suggestive of an ongoing merger. Even so, the X-ray mass inferred from the hydrostatic equilibrium assumption appears to be consistent with the lensing mass from the Einstein radius of the system. We find significant absorption in the soft X-ray spectrum of the faintest quasar image, which can be caused by an intervening material at either the lens or source redshift. The X-ray flux ratios between the quasar images (after correcting for absorption) are in reasonable agreement with those at optical and radio wavelengths, and all the flux ratios are inconsistent with those predicted by simple mass models. This implies that microlensing effect is not significant for this system and dark matter substructure is mainly responsible for the anomalous flux ratios.

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Section: Comparison With Optical and Radio Flux Ratiosmentioning

confidence: 99%

THECHANDRAVIEW OF THE LARGEST QUASAR LENS SDSS J1029+2623

Ota

Oguri

Dai

et al. 2012

ApJ

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“…However, it is well known observationally (yet unexplained physically) that ∼10%-30% of AGNs have (1) Xray spectra that show no absorption and (2) optical spectra that suggest obscuration (e.g., Pappa et al 2001;Panessa & Bassani 2002;Barcons et al 2003;Georgantopoulos & Zezas 2003;Caccianiga et al 2004;Corral et al 2005;Wolter et al 2005;Mateos et al 2005;Tozzi et al 2006). The opposite effect, i.e., (1) X-ray spectra that show absorption and (2) optical spectra that suggest no obscuration, has also been observed (e.g., Silverman et al 2005 found that ∼15% of X-ray hard AGNs in ChaMP are BLAGNs; other examples can be found in Comastri et al 2001;Wilkes et al 2002;Fiore et al 2003;Brusa et al 2003;Akiyama et al 2003;Silverman et al 2005;Gallagher et al 2006;Hall et al 2006;Tajer et al 2007).…”

Section: Introductionmentioning

confidence: 99%

The Optx Project. Iii. X-Ray Versus Optical Spectral Type for Active Galactic Nuclei

Trouille

Barger

Cowie

et al. 2009

ApJ

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We compare the optical spectral types with the X-ray spectral properties for a uniformly selected (sources with fluxes greater than the 3σ level and above a flux limit of f 2-8 keV > 3.5 × 10 −15 erg cm −2 s −1 ), highly spectroscopically complete (>80% for f 2-8 keV > 10 −14 erg cm −2 s −1 and >60% below) 2-8 keV X-ray sample observed in three Chandra fields (CLANS, CLASXS, and the CDF-N) that cover ∼1.2 deg 2 . For our sample of 645 spectroscopically observed sources, we confirm that there is significant overlap of the X-ray spectral properties, as determined by the effective photon indices, Γ eff , obtained from the ratios of the 0.5-2 keV to 2-8 keV counts, for the different optical spectral types. For example, broad-line active galactic nuclei (AGNs) are expected to be unobscured and hence X-ray soft (Γ eff 1.2), yet we find 20% ± 3% have Γ eff < 1.2. Non-broad-line AGNs are expected to be obscured and hence X-ray hard (Γ eff < 1.2), yet we find 33% ± 4% have Γ eff 1.2. Thus, one cannot use the X-ray spectral classifications and the optical spectral classifications equivalently. Since it is not understood how X-ray and optical classifications relate to the obscuration of the central engine, we strongly advise against a mixed classification scheme, as it can only complicate the interpretation of X-ray AGN samples. We confirm the dependence of optical spectral type on X-ray luminosity, and for z < 1, we find a similar luminosity dependence of Γ eff . However, this dependence breaks down at higher redshifts due to the highly redshift-dependent nature of Γ eff . We therefore also caution that any classification scheme which depends on Γ eff is likely to suffer from serious redshift bias.

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“…In addition to WLQs, there exists a population of red type 1 quasars that can be X-ray weak (e.g., Wilkes et al 2005;Hall et al 2006). Previous X-ray studies have demonstrated that quasars with the reddest optical colors at their redshifts are more likely to be X-ray absorbed than typical quasars (e.g., Wilkes et al 2005), although some of the reddest quasars may show no evidence of X-ray absorption or X-ray weakness (e.g., Hall et al 2006). These optically red quasars may be X-ray obscured by dusty gas, which also extincts the UV continuum, perhaps from a starburst disk surrounding their accreting SMBHs (e.g., Hickox & Alexander 2018).…”

Section: X-ray Weak Red Quasarsmentioning

confidence: 99%

“…The ∆(g − i) distribution for SDSS quasars is roughly Gaussian but has a distinct red tail with ∆(g − i) 0.2, which is indicative of dust reddening (Richards et al 2003). Based on the ∆(g − i) distribution, Hall et al (2006) adopted ∆(g − i) > 0.2 to select red quasars for X-ray study.…”

Section: X-ray Weak Red Quasarsmentioning

confidence: 99%

On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey

Brandt²,

Timlin

et al. 2020

Preprint

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We investigate systematically the X-ray emission from type 1 quasars using a sample of 1825 Sloan Digital Sky Survey (SDSS) non-broad absorption line (non-BAL) quasars with Chandra archival observations. A significant correlation is found between the X-ray-to-optical power-law slope parameter (α OX ) and the 2500 Å monochromatic luminosity (L 2500 Å), and the X-ray weakness of a quasar is assessed via the deviation of its α OX value from that expected from this relation. We demonstrate the existence of a population of non-BAL X-ray weak quasars, and the fractions of quasars that are X-ray weak by factors of ≥ 6 and ≥ 10 are 5.8 ± 0.7% and 2.7 ± 0.5%, respectively. We classify the X-ray weak quasars (X-ray weak by factors of ≥ 6) into three categories based on their optical spectral features: weak emission-line quasars (WLQs; C iv REW < 16 Å), red quasars (∆(g − i) > 0.2), and unclassified X-ray weak quasars. The X-ray weak fraction of 35 +12 −9 % within the WLQ population is significantly higher than that within non-WLQs, confirming previous findings that WLQs represent one population of X-ray weak quasars. The X-ray weak fraction of 13 +5 −3 % within the red quasar population is also considerably higher than that within the normal quasar population. The unclassified X-ray weak quasars do not have unusual optical spectral features, and their X-ray weakness may be mainly related to quasar X-ray variability.

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ChandraObservations of Red Sloan Digital Sky Survey Quasars

Cited by 20 publications

References 63 publications

THECHANDRAVIEW OF THE LARGEST QUASAR LENS SDSS J1029+2623

THECHANDRAVIEW OF THE LARGEST QUASAR LENS SDSS J1029+2623

The Optx Project. Iii. X-Ray Versus Optical Spectral Type for Active Galactic Nuclei

On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey

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