We analyze the X-ray, optical, and mid-infrared data of a changing-look Seyfert galaxy sdssj15 at $zsimeq0.086$. Over a period of one decade (2009 - 2018), its broad H$alpha$ line intensity increased by a factor of $sim$4. Meanwhile, the X-ray emissi
on in 2014 as observed by chandra was about five times brighter than that in 2010 by {it Suzaku}, and the corresponding emissions in V-band, mid-infrared W1 band brighten by $sim$ 0.18, 0.32 mag, respectively. Moreover, the absorption in X-rays is moderate and stable, i.e. ${rm N_{H}}sim 10^{21} {rm cm^{-2}}$, but the X-ray spectrum becomes harder in the 2014 chandra bright state (i.e. photon index $Gamma = 1.52^{+0.06}_{-0.06}$) than that of the 2010 suzaku low state ($Gamma=2.03^{+0.22}_{-0.21}$). With an Eddington ratio being lower than a few percent, the inner region of the accretion disk in sdssj15 is likely a hot accretion flow. We then compile from literature the X-ray data of changing-look AGNs, and find that they generally follow the well-established V-shaped correlation in AGNs, that is, above a critical turn-over luminosity the X-ray spectra soften with the increasing luminosity, and below that luminosity the trend is reversed in a way of harder when brighter. This presents a direct evidence that CL-AGNs have distinctive changes in not only the optical spectral type, but also the X-ray spectral shape. The similarity in the X-ray spectral evolution between CL-AGNs and black hole X-ray binaries indicates that the observed CL-AGNs phenomena may relate to the state transition in accretion physics.
A brief Chandra observation of the ultraluminous quasar, SDSS J010013.02+280225.8 at redshift 6.326, showed it to be a relatively bright, soft X-ray source with a count rate of about 1 ct/ks. In this paper we present results for the quasar from a 65k
s XMM-Newton observation, which well constrains its spectral shape. The quasar is clearly detected with a total of $sim$ 460 net counts in the 0.2-10 keV band. The spectrum is characterised by a simple power-law model with photon index of $Gamma = 2.30^{+0.10}_{-0.10}$, and the intrinsic 2-10 keV luminosity is $3.14times10^{45}$ erg $text{s}^{-1}$. The 1 $sigma$ upper limit to any intrinsic absorption column density is $N_{H} = 6.07times 10^{22} {text{cm}}^{-2}$. No significant iron emission lines were detected. We derive the X-ray-to-optical flux ratio $alpha_{text{ox}}$ of $-1.74pm$0.01, consistent with the values found in other quasars of comparable ultraviolet luminosity. We did not detect significant flux variations either in the XMM-Newton exposure or between XMM-Newton and XMM-Newton observations, which are separated by $sim$ 8 months. The X-ray observation enables the bolometric luminosity to be calculated after modelling the spectral energy distribution: the accretion rate is found to be sub-Eddington.
We report exploratory chandra observation of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.30. The quasar is clearly detected by chandra with a possible component of extended emission. The rest-frame 2-10 keV luminosity is 9.0$^{+9.
1}_{-4.5}$ $times$ 10$^{45}$ erg s$^{-1}$ with inferred photon index of $Gamma$ = 3.03$^{+0.78}_{-0.70}$. This quasar is X-ray bright, with inferred X-ray-to-optical flux ratio aox $=-1.22^{+0.07}_{-0.05}$, higher than the values found in other quasars of comparable ultraviolet luminosity. The properties inferred from this exploratory observation indicate that this ultraluminous quasar might be growing with super-Eddington accretion and probably viewed with small inclination angle. Deep X-ray observation will help to probe the plausible extended emission and better constraint the spectral features for this ultraluminous quasar.
