Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The properties of the X-ray corona in the distant ($z=3.91$) quasar APM
  08279+5255   We present new joint XMM-Newton and NuSTAR observations of APM 08279+5255, a
gravitationally-lensed, broad-absorption line quasar ($z=3.91$). After showing
a fairly stable flux ($f_{\rm2-10}\simeq4-5.5\times10^{-13}\rm~erg~s^{-1}$)
from 2000 to 2008, APM 08279+5255 was found in a fainter state in the latest
X-ray exposures ($f_{\rm2-10}\simeq2.7\times10^{-13}\rm~erg~s^{-1}$), which can
likely be ascribed to a lower X-ray activity. Moreover, the 2019 data present a
prominent Fe K$\alpha$ emission line and do not show any significant absorption
line. This fainter state, coupled to the first hard X-ray sampling of APM
08279+5255, allowed us to measure X-ray reflection and the high-energy cutoff
in this source for the first time. From the analysis of previous XMM-Newton and
Chandra observations, X-ray reflection is demonstrated to be a long-lasting
feature of this source, but less prominent prior to 2008, possibly due to a
stronger primary emission. The estimated high-energy cutoff ($E_{\rm
cut}=99_{-35}^{+91}$ keV) sets a new redshift record for the farthest ever
measured and places APM 08279+5255 in the allowed region of the
compactness-temperature diagram of X-ray coronae, in agreement with previous
results on high-$z$ quasars.

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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ph
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The categories of this paper are: adap-org
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The categories of this paper are: cond-mat
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-ex