Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quasars as standard candles I: The physical relation between disc and
  coronal emission   A tight non-linear relation exists between the X-ray and UV emission in
quasars (i.e. $L_{\rm X}\propto L_{\rm UV}^{\gamma}$), with a dispersion of
$\sim$0.2~dex over $\sim$3~orders of magnitude in luminosity. Here we propose a
modified version of this relation which involves the broad emission lines'
full-width at half maximum, $L_{\rm X}\propto L_{\rm
UV}^{\hat\gamma}\upsilon_{\rm fwhm}^{\hat\beta}$. We interpret this new
relation through a simple, {\it ad-hoc} model of accretion disc corona, derived
from previous works where it is assumed that reconnection and magnetic loops
above the accretion disc can account for the production of the primary X-ray
radiation. We find that the monochromatic optical-UV (2500 \AA) and X-ray (2
keV) luminosities depend on the black hole mass and accretion rate as $L_{\rm
UV}\propto M_{\rm BH}^{4/3} (\dot{M}/\dot{M}_{\rm Edd})^{2/3}$ and $L_{\rm
X}\propto M_{\rm BH}^{19/21} (\dot{M}/\dot{M}_{\rm Edd})^{5/21}$, respectively.
Assuming a broad line region size function of the disc luminosity $R_{\rm
blr}\propto L_{\rm disc}^{0.5}$ we finally have that $L_{\rm X}\propto L_{\rm
UV}^{4/7} \upsilon_{\rm fwhm}^{4/7}$. Such relation is remarkably consistent
with the slopes and the normalization obtained from a fit of a sample of 545
optically selected quasars from SDSS DR7 cross matched with the latest
XMM-Newton catalogue 3XMM-DR6. The homogeneous sample used here has a
dispersion of 0.21 dex, which is much lower than previous works in the
literature and suggests a tight physical relation between the accretion disc
and the X-ray emitting corona. The proposed new relation does not evolve with
time, and thus it can be employed as a cosmological indicator to robustly
estimate cosmological parameters.

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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: stat
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The categories of this paper are: funct-an
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: gr-qc
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The categories of this paper are: ao-sci
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The categories of this paper are: quant-ph
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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga