On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey. (arXiv:2008.02277v1 [astro-ph.GA])

On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey. (arXiv:2008.02277v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Pu_X/0/1/0/all/0/1">Xingting Pu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Luo_B/0/1/0/all/0/1">B. Luo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brandt_W/0/1/0/all/0/1">W. N. Brandt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Timlin_J/0/1/0/all/0/1">John D. Timlin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_H/0/1/0/all/0/1">Hezhen Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ni_Q/0/1/0/all/0/1">Q. Ni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wu_J/0/1/0/all/0/1">Jianfeng Wu</a>

We investigate systematically the X-ray emission from type 1 quasars using a
sample of 1825 Sloan Digital Sky Survey (SDSS) non-broad absorption line
(non-BAL) quasars with Chandra archival observations. A significant correlation
is found between the X-ray-to-optical power-law slope parameter ($alpha_{rm
OX}$) and the 2500 $r{A}$ monochromatic luminosity ($L_{rm 2500~r{A}}$), and
the X-ray weakness of a quasar is assessed via the deviation of its
$alpha_{rm OX}$ value from that expected from this relation. We demonstrate
the existence of a population of non-BAL X-ray weak quasars, and the fractions
of quasars that are X-ray weak by factors of $ge6$ and $ge10$ are
$5.8pm0.7%$ and $2.7pm0.5%$, respectively. We classify the X-ray weak
quasars (X-ray weak by factors of $ge6$) into three categories based on their
optical spectral features: weak emission-line quasars (WLQs; CIV REW
$<16~r{A}$), red quasars ($Delta(g-i)>0.2$), and unclassified X-ray weak
quasars. The X-ray weak fraction of $35_{- 9}^{+12}%$ within the WLQ
population is significantly higher than that within non-WLQs, confirming
previous findings that WLQs represent one population of X-ray weak quasars. The
X-ray weak fraction of $13_{- 3}^{+ 5}%$ within the red quasar population is
also considerably higher than that within the normal quasar population. The
unclassified X-ray weak quasars do not have unusual optical spectral features,
and their X-ray weakness may be mainly related to quasar X-ray variability.

We investigate systematically the X-ray emission from type 1 quasars using a
sample of 1825 Sloan Digital Sky Survey (SDSS) non-broad absorption line
(non-BAL) quasars with Chandra archival observations. A significant correlation
is found between the X-ray-to-optical power-law slope parameter ($alpha_{rm
OX}$) and the 2500 $r{A}$ monochromatic luminosity ($L_{rm 2500~r{A}}$), and
the X-ray weakness of a quasar is assessed via the deviation of its
$alpha_{rm OX}$ value from that expected from this relation. We demonstrate
the existence of a population of non-BAL X-ray weak quasars, and the fractions
of quasars that are X-ray weak by factors of $ge6$ and $ge10$ are
$5.8pm0.7%$ and $2.7pm0.5%$, respectively. We classify the X-ray weak
quasars (X-ray weak by factors of $ge6$) into three categories based on their
optical spectral features: weak emission-line quasars (WLQs; CIV REW
$<16~r{A}$), red quasars ($Delta(g-i)>0.2$), and unclassified X-ray weak
quasars. The X-ray weak fraction of $35_{- 9}^{+12}%$ within the WLQ
population is significantly higher than that within non-WLQs, confirming
previous findings that WLQs represent one population of X-ray weak quasars. The
X-ray weak fraction of $13_{- 3}^{+ 5}%$ within the red quasar population is
also considerably higher than that within the normal quasar population. The
unclassified X-ray weak quasars do not have unusual optical spectral features,
and their X-ray weakness may be mainly related to quasar X-ray variability.

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