2019/11/30 by Y. L. Ai, Liming Dou, Ai, Yanli +17 · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · pdf · doi:10.48550/arxiv.1912.00164
openalex publication_date 2019/11/30 · openalex created_date 2019/12/05 · openalex updated_date 2026/07/28
We analyze the X-ray, optical, and mid-infrared data of a "changing-look" Seyfert galaxy \sdssj15 at z≃0.086. Over a period of one decade (2009 - 2018), its broad Hα line intensity increased by a factor of ∼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 ∼ 0.18, 0.32 mag, respectively. Moreover, the absorption in X-rays is moderate and stable, i.e. \rm NH∼ 1021 \rm cm-2, but the X-ray spectrum becomes harder in the 2014 \chandra bright state (i.e. photon index Γ= 1.52+0.06-0.06) than that of the 2010 \suzaku low state (Γ=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.