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Register a new userDetectability of low energy X-ray spectral components in type 1 AGN
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In this paper we examine the percentage of type 1 AGN which require the inclusion of a soft excess component and/or significant cold absorption in the modelling of their X-ray spectra obtained by XMM-Newton. We do this by simulating spectra which mimic typical spectral shapes in order to find the maximum detectability expected at different count levels. We then apply a correction to the observed percentages found for the Scott et al. (2011) sample of 761 sources. We estimate the true percentage of AGN with a soft excess component to be 75+/-23%, suggesting that soft excesses are ubiquitous in the X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count spectra in narrow z bins in which additional spectral components were not originally detected, we show that the soft excess feature is recovered with a mean temperature kT and blackbody to power-law normalisation ratio consistent with those of components detected in individual high count spectra. Cold absorption with nH values broadly consistent with those reported in individual spectra are also recovered. We suggest such intrinsic cold absorption is found in a minimum of ~5% of type 1 AGN and may be present in up to ~10%.
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We create broadband SEDs of 761 type 1 AGN. The Scott et al. sample, created by a cross-correlation of the optical SDSS DR5 quasar catalogue and the 2XMMi catalogue of serendipitous X-ray sources, is further matched with the FIRST catalogue of radio sources, the WISE MIR all-sky data release, the 2MASS NIR point source catalogue, the UKIDSS DR9 Large Area Survey and the GALEX all-sky and medium UV imaging surveys. This allows broadband SEDs covering log(nu)~9.2-18.1 to be created. We investigate variations in the SED shape by binning a subsample of 237 AGN with the best quality SEDs according to their X-ray spectral parameters, their AGN sub-type and their luminosity, black hole mass and Eddington ratio. The AGN sub-populations show some significant differences in their SEDs; X-ray absorbed AGN show a deficit of emission at X-ray/UV frequencies and an excess in the MIR consistent with absorption and re-emission, radio-loud AGN show increased radio and X-ray emission, consistent with the presence of a jet component in addition to the emission seen from radio-quiet AGN and the SEDs of NLS1s only differ from other type 1s in the X-ray regime, suggesting any physical differences are limited to their X-ray emitting region. Binning the AGN according to underlying physical parameters reveals more subtle differences in the SEDs. The X-ray spectral slope does not appear to have any influence or dependence on the multiwavelength emission in the rest of the SED. The contribution of X-rays to Lbol is lower in higher luminosity sources, and relatively more emission in the optical/UV is seen in AGN with higher Lx. Variations in the relative flux and peak frequency of the BBB are observed and may suggest higher inner disc temperatures with increasing accretion rates. Overall, we find that the diversity in the SED shapes is relatively small, and we find no apparent single driver for the variations.
We study the X-ray properties of a sample of 14 optically-selected low-mass AGN whose masses lie within the range 1E5 -2E6 M(solar) with XMM-Newton. Only six of these low-mass AGN have previously been studied with sufficient quality X-ray data, thus, we more than double the number of low-mass AGN observed by XMM-Newton with the addition of our sample. We analyze their X-ray spectral properties and variability and compare the results to their more massive counterparts. The presence of a soft X-ray excess is detectable in all five objects which were not background dominated at 2-3 keV. Combined with previous studies, this gives a total of 8 low-mass AGN with a soft excess. The low-mass AGN exhibit rapid, short-term variability (hundreds to thousands of seconds) as well as long-term variability (months to years). There is a well-known anti-correlation between black hole mass and variability amplitude (normalized excess variance). Comparing our sample of low-mass AGN with this relation we find that all of our sample lie below an extrapolation of the linear relation. Such a flattening of the relation at low masses (below about 1E6 M(solar)) is expected if the variability in all AGN follows the same shape power spectrum with a break frequency that is dependent on mass. Finally, we also found two objects that show significant absorption in their X-ray spectrum, indicative of type 2 objects, although they are classified as type 1 AGN based on optical spectra.
The mid-infrared to ultraviolet (0.1 -- 10 $mu m$) spectral energy distribution (SED) shapes of 407 X-ray-selected radio-quiet type 1 AGN in the wide-field ``Cosmic Evolution Survey (COSMOS) have been studied for signs of evolution. For a sub-sample of 200 radio-quiet quasars with black hole mass estimates and host galaxy corrections, we studied their mean SEDs as a function of a broad range of redshift, bolometric luminosity, black hole mass and Eddington ratio, and compared them with the Elvis et al. (1994, E94) type 1 AGN mean SED. We found that the mean SEDs in each bin are closely similar to each other, showing no statistical significant evidence of dependence on any of the analyzed parameters. We also measured the SED dispersion as a function of these four parameters, and found no significant dependencies. The dispersion of the XMM-COSMOS SEDs is generally larger than E94 SED dispersion in the ultraviolet, which might be due to the broader ``window function for COSMOS quasars, and their X-ray based selection.
We have identified spectral features in the late-time X-ray afterglow of the unusually long, slow-decaying GRB 130925A using NuSTAR, Swift-XRT, and Chandra. A spectral component in addition to an absorbed power-law is required at $>4sigma$ significance, and its spectral shape varies between two observation epochs at $2times10^5$ and $10^6$ seconds after the burst. Several models can fit this additional component, each with very different physical implications. A broad, resolved Gaussian absorption feature of several keV width improves the fit, but it is poorly constrained in the second epoch. An additive black body or second power-law component provide better fits. Both are challenging to interpret: the blackbody radius is near the scale of a compact remnant ($10^8$ cm), while the second powerlaw component requires an unobserved high-energy cutoff in order to be consistent with the non-detection by Fermi-LAT.
This work presents the catalogue of optical spectral properties for all X-ray selected SPIDERS active galactic nuclei (AGN) up to SDSS DR14. SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV programme that is currently conducting optical spectroscopy of the counterparts to the X-ray selected sources detected in the ROSAT all-sky survey and the XMM-Newton slew survey in the footprint of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The SPIDERS DR14 sample is the largest sample of X-ray selected AGN with optical spectroscopic follow-up to date. The catalogue presented here is based on a clean sample of 7344 2RXS ($rm bar{z}$ = 0.5) and 1157 XMM-Newton slew survey ($rm bar{z}$ = 0.4) type 1 AGN with spectroscopic coverage of the H$rm beta$ and/or MgII emission lines. Visual inspection results for each object in this sample are available from a combination of literature sources and the SPIDERS group, which provide both reliable redshifts and source classifications. The spectral regions around the H$rm beta$ and MgII emission lines have been fit in order to measure both line and continuum properties, estimate bolometric luminosities, and provide black hole mass estimates using the single-epoch (or photoionisation) method. The use of both H$rm beta$ and MgII allows black hole masses to be estimated up to z $rm simeq$ 2.5. A comparison is made between the spectral properties and black hole mass estimates derived from H$rm beta$ and MgII using the subsample of objects which have coverage of both lines in their spectrum. These results have been made publicly available as an SDSS-IV DR14 value added catalogue.
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