X-ray spectra of a large sample of quasars with ASCA

Abstract

A B S T R A C TThe results from an X-ray spectral analysis of a large sample of quasars, observed with ASCA, are presented. The sample was selected to include all ASCA observations of quasars, with z . 0X05 and M V , 223X0Y available up to 1998 January. The data reduction leaves 62 quasars, 35 of which are radio-loud and 27 radio-quiet, suitable for spectral analysis. Differences are found between the radio-quiet quasars (RQQs) and the radio-loud quasars (RLQs): the RLQs have flatter X-ray spectra G , 1X6Y with little iron line emission or reflection, and are more X-ray luminous than the softer G , 1X9 RQQs, in agreement with previous studies. A correlation between G and optical Hb was also found for the radio-quiet quasars in this sample, whereby the steepest X-ray spectra tend to be found in those objects with small Hb widths. The correlation is significant at .99 per cent confidence, confirming the well-known trend between G and Hb FWHM in Seyfert 1s, but at higher luminosities.Other spectral complexities are observed from this sample. A soft X-ray excess, with blackbody temperatures in the range 100±300 eV, is seen in many low-z radio-quiet quasars. In most cases the temperatures are probably too hot to originate directly from the disc and could imply that some reprocessing is involved. Iron K-line emission features are also found in the RQQs, but often from partially ionized material. Indeed, in the highest-luminosity RQQs there is neither evidence for iron line emission nor the reflection component expected from disc reflection models. These observations can be explained by an increase in the quasar accretion rate with luminosity, leading to an increase in the ionization state of the surface layers of the disc. The occurrence of ionized or`warm' absorbers is rare in this sample, with only five detections in low-z objects. However, excess neutral X-ray absorption is found towards several of the high-z, predominantly radio-loud, quasars. Although found to increase with quasar redshift, this`intrinsic' absorption may be associated with radio-loud active galactic nuclei.

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

“…Our findings are also consistent with previous results showing low levels of reflection for high-redshift quasars (Vignali et al 1999;Reeves & Turner 2000;Page et al 2005), although we note that Ricci et al (2011) found higher levels of reflection from Seyfert2s than from Seyfert1s. Figure 8 (bottom panels) shows unobscured and obscured sources as empty and filled data points, respectively, and does not allow a firm conclusion on this point for Seyfert-like luminosity sources.…”

X‐Raying the Ultraluminous Infrared Starburst Galaxy and Broad Absorption Line QSO Markarian 231 withChandra

“…Based on ROSAT data, Boller, Brandt, & Fink (1996) and Laor et al (1997) found a significant correlation between the X-ray photon indexes of radio-quiet AGNs and the value for the FWHM H , where those AGNs with the narrowest broad Balmer lines, narrow-line Seyfert 1 galaxies (NLS1s), tended toward the steep end of the distribution of C. Subsequent work with ASCA in the 2-10 keV band has extended this finding to higher energy, although the spread of C in the 2-10 keV band is much smaller (e.g., Brandt, Mathur, & Elvis 1997;Reeves & Turner 2000). Mrk 231 has relatively narrow Balmer emission lines, FWHM H ¼ 2870 km s À1 (Boroson & Meyers 1992) and FWHM H ¼ 3000 km s À1 (Lípari, Terlevich, & Macchetto 1993), particularly for a QSO of its luminosity.…”

“…In particular, there were positive residuals below 1.0 keV and above 5 keV. Also, the best-fitting photon index, À ¼ 0:46 AE 0:09, was unusually hard; the typical photon index for a radio-quiet QSO is in the range À ¼ 1:7-2.3 (e.g., Reeves & Turner 2000;George et al 2000). As Mrk 231 hosts a starburst ring within 1 00 of its nucleus (Bryant & Scoville 1996;Carilli et al 1998;Taylor et al 1999), a plausi- ble additional component to add is a Raymond-Smith thermal plasma (Raymond & Smith 1977).…”

“…Based on the ASCA correlation for radio-quiet QSOs between C and the FWHM H , a photon index of $2.1 for Mrk 231 would be more typical (Reeves & Turner 2000). In addition to the unusually steep photon index, the lack of strong Fe K line emission accompanying a reflected continuum is also striking.…”

Universal spectral shape of high accretion rate AGN

“…MCG -6-15-30 (Reynolds et al 1997). Also a recent study of the X-ray spectra of AGN with X-ray luminosity range between 10 41 erg s −1 and 10 47 erg s −1 did not reveal any trend in the X-ray slope with the luminosity (Reeves & Turner 2000).…”