Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: ROSAT HRI Monitoring of Extreme X-ray Variability in the Narrow-Line
  Quasar PHL 1092   We report results from an 18-day ROSAT HRI monitoring campaign on the
ultrasoft Narrow-Line Seyfert 1 (NLS1) class quasar PHL 1092. This luminous,
radio-quiet quasar showed strong X-ray variability in a short ROSAT PSPC
observation, and ROSAT HRI monitoring of the similar object IRAS 13224-3809
revealed extreme variability on intermediate timescales. We wanted to determine
whether remarkable X-ray variability persistently occurs in PHL 1092, and we
also wanted to search for outstanding variability events that constrain
emission processes. Given the large luminosity of PHL 1092 (about 5x10^{45}
erg/s in the HRI band), we detect extremely rapid and large-amplitude X-ray
variability throughout our monitoring. The maximum observed variability
amplitude is a factor of about 14, and in the most rapid variability event the
HRI count rate increases by a factor of about 3.8 in a rest-frame time interval
of < 3580 s. The most rapid event has a rate change of luminosity of >
1.3x10^{42} erg/s^2, making it the most extreme such event we are aware of from
a radio-quiet quasar. Standard `radiative efficiency limit' arguments imply a
radiative efficiency larger than can be achieved by accretion onto a Kerr black
hole rotating at the maximum plausible rate, although we point out that such
arguments depend upon the geometry of initial radiation release. Relativistic
motions of the X-ray source are probably causing the radiative efficiency limit
to break down; such relativistic motions have also been inferred in the similar
NLS1-class quasar PKS 0558--504.

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The categories of this paper are: plasm-ph
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The categories of this paper are: math-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: physics
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The categories of this paper are: solv-int
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The categories of this paper are: cs
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: econ
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The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga