X-ray spectral shape variations in changing-look Seyfert galaxy SDSSJ155258+273728. (arXiv:1912.00164v1 [astro-ph.GA])

X-ray spectral shape variations in changing-look Seyfert galaxy SDSSJ155258+273728. (arXiv:1912.00164v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ai_Y/0/1/0/all/0/1">Yanli Ai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dou_L/0/1/0/all/0/1">Liming Dou</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_C/0/1/0/all/0/1">Chenwei Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sun_L/0/1/0/all/0/1">Luming Sun</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xie_F/0/1/0/all/0/1">Fu-Guo Xie</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yao_S/0/1/0/all/0/1">Su Yao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wu_X/0/1/0/all/0/1">Xue-Bing Wu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_T/0/1/0/all/0/1">Tinggui Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shu_X/0/1/0/all/0/1">Xinwen Shu</a>

We analyze the X-ray, optical, and mid-infrared data of a Seyfert galaxy
SDSSJ155258+273728 at $zsimeq0.086$. The broad H$alpha$ line intensity
increased by a factor of $sim$4 in a decade. Accompanied with this, the X-ray
emission detected by Chandra was about five times brighter than that from
Suzaku in 2010, and the corresponding V-band, mid-infrared W1 band brighten
$sim$ 0.18, 0.32 mag, respectively. The X-ray spectrum flattens in the Chandra
bright state with a photon index of $1.52^{+0.06}_{-0.06}$, compared to the
value of $2.03^{+0.22}_{-0.21}$ in the Suzaku low state. Only moderate
absorption was detected in all the X-ray observations with ${rm N_{H}}sim
10^{21} {rm cm^{-2}}$. The accretion rate of SDSSJ155258+273728 is low with an
Eddington ratio below a few percent, suggesting that the inner region of the
accretion disk is possibly a hot accretion flow. By compiling the X-ray data
from literatures, we find that “changing-look” AGNs generally follow the
well-studied correlation shape (“V-shape”) 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 direct evidence that CL-AGNs have distinctive changes
in not only the optical spectral type, but also the X-ray spectral shape. The
similarity of the X-ray spectral evolution between CL-AGNs and black hole X-ray
binaries in their outbursts indicates that the observed CL-AGNs phenomena may
relate to the accretion state transition.

We analyze the X-ray, optical, and mid-infrared data of a Seyfert galaxy
SDSSJ155258+273728 at $zsimeq0.086$. The broad H$alpha$ line intensity
increased by a factor of $sim$4 in a decade. Accompanied with this, the X-ray
emission detected by Chandra was about five times brighter than that from
Suzaku in 2010, and the corresponding V-band, mid-infrared W1 band brighten
$sim$ 0.18, 0.32 mag, respectively. The X-ray spectrum flattens in the Chandra
bright state with a photon index of $1.52^{+0.06}_{-0.06}$, compared to the
value of $2.03^{+0.22}_{-0.21}$ in the Suzaku low state. Only moderate
absorption was detected in all the X-ray observations with ${rm N_{H}}sim
10^{21} {rm cm^{-2}}$. The accretion rate of SDSSJ155258+273728 is low with an
Eddington ratio below a few percent, suggesting that the inner region of the
accretion disk is possibly a hot accretion flow. By compiling the X-ray data
from literatures, we find that “changing-look” AGNs generally follow the
well-studied correlation shape (“V-shape”) 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 direct evidence that CL-AGNs have distinctive changes
in not only the optical spectral type, but also the X-ray spectral shape. The
similarity of the X-ray spectral evolution between CL-AGNs and black hole X-ray
binaries in their outbursts indicates that the observed CL-AGNs phenomena may
relate to the accretion state transition.

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