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تسجيل مستخدم جديدX-ray spectral shape variations in changing-look Seyfert galaxy SDSSJ155258+273728
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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 emission 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.
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