A FULL YEAR'SCHANDRAEXPOSURE ON SLOAN DIGITAL SKY SURVEY QUASARS FROM THECHANDRAMULTIWAVELENGTH PROJECT

Abstract

We study the spectral energy distributions and evolution of a large sample of optically selected quasars from the Sloan Digital Sky Survey that were observed in 323 Chandra images analyzed by the Chandra Multiwavelength Project. Our highest-confidence matched sample includes 1135 X-ray detected quasars in the redshift range 0.2 < z < 5.4, representing some 36 Msec of effective exposure. We provide catalogs of QSO properties, and describe our novel method of calculating X-ray flux upper limits and effective sky coverage. Spectroscopic redshifts are available for about 1/3 of the detected sample; elsewhere, redshifts are estimated photometrically. We detect 56 QSOs with redshift z > 3, substantially expanding the known sample. We find no evidence for evolution out to z ∼ 5 for either the X-ray photon index Γ or for the ratio of optical/UV to X-ray flux α ox . About 10% of detected QSOs show best-fit intrinsic absorbing columns greater than 10 22 cm −2 , but the fraction might reach ∼1/3 if most nondetections are absorbed. We confirm a significant correlation between α ox and optical luminosity, but it flattens or disappears for fainter (M B −23) active galactic nucleus (AGN) alone. We report significant hardening of Γ both toward higher X-ray luminosity, and for relatively X-ray loud quasars. These trends may represent a relative increase in nonthermal X-ray emission, and our findings thereby strengthen analogies between Galactic black hole binaries and AGN. For uniformly selected subsamples of narrow-line Seyfert 1s and narrow absorption line QSOs, we find no evidence for unusual distributions of either α ox or Γ.

Reflection from the strong gravity regime in a lensed quasar at redshift z = 0.658

“…Nonetheless, this analysis clearly demonstrates the presence of a significant contribution from a reflection component to the X-ray spectrum of this z = 0.658 quasar. The properties of RX J1131-3 1231 are consistent [11,13,12,14,16] with the known observational characteristics of quasars at 0.5 z 1, and our results suggest that the relativistic reflection component from the large population of unobscured quasars expected in this epoch [17] could significantly contribute in the 20-30 keV band of the Cosmic X-ray background.Although questions have previously been raised over whether reflection is a unique interpretation for the features observed in AGNs, the amassed evidence points towards this theoretical framework [24, 29], and reached culmination with the launch of NuSTAR and the strong confirmation of relativistic disk reflection from a rapidly spinning supermassive black hole at the centre of the nearby galaxy NGC 1365 [6]. Nonetheless, there still remain possible systematic uncertainties, for example, due to the intrinsic assumption that the disk truncates at the innermost stable circular orbit.…”

“…Nonetheless, this analysis clearly demonstrates the presence of a significant contribution from a reflection component to the X-ray spectrum of this z = 0.658 quasar. The properties of RX J1131-3 1231 are consistent [11,13,12,14,16] with the known observational characteristics of quasars at 0.5 z 1, and our results suggest that the relativistic reflection component from the large population of unobscured quasars expected in this epoch [17] could significantly contribute in the 20-30 keV band of the Cosmic X-ray background.…”

“…Prior studies have revealed the presence of a soft-excess in 90% of quasars at[11, 12] z 1.7, and broad Fe-lines are also seen in 25% of these objects [11,13], suggesting that reflection is also prevalent in these distant AGNs. However, due to the inadequate S/N resulting from their greater distances, the X-ray spectra of these quasars were necessarily modeled using simple phenomenological parameterizations [12,14].Gravitational lensing offers a rare opportunity to study the innermost relativistic region in distant quasars [15,16], by acting as a natural telescope and magnifying the light from these sources. Quasars located between 0.5 z 1 are considerably more powerful than local Seyferts and are known to be a major contributor to the Cosmic X-ray background [17], making them objects of particular cosmological importance.…”

“…Prior studies have revealed the presence of a soft-excess in 90% of quasars at [11,12] z 1.7, and broad Fe-lines are also seen in 25% of these objects [11,13], suggesting that reflection is also prevalent in these distant AGNs. However, due to the inadequate S/N resulting from their greater distances, the X-ray spectra of these quasars were necessarily modeled using simple phenomenological parameterizations [12,14].…”

The X-ray to optical-UV luminosity ratio of X-ray selected type 1 AGN in XMM-COSMOS

“…These studies, based on Einstein observations, found a mean value of α ox in the range 1.3−1.45. Subsequently, many investigations have been performed (e.g., Yuan et al 1998;Vignali et al 2003;Strateva et al 2005;Steffen et al 2006, hereafter S06;Just et al 2007, hereafter J07; Kelly et al 2008;Green et al 2009;Young et al 2009) which were mainly based on AGN samples selected from the Sloan Digital Sky Survey (SDSS). Most of the previous studies on the relationship between α ox , luminosity and redshift A&A 512, A34 (2010) were based on large samples of optically selected type 1 AGN with a high fraction of X-ray detections.…”