Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The variability properties of X-ray steep and X-ray flat quasars   We have studied the variability of 6 low redshift, radio quiet `PG' quasars
on three timescales (days, weeks, and months) using the ROSAT HRI. The quasars
were chosen to lie at the two extreme ends of the ROSAT PSPC spectral index
distribution and hence of the H$\beta$ FWHM distribution. The observation
strategy has been carefully designed to provide even sampling on these three
basic timescales and to provide a uniform sampling among the quasars We have
found clear evidence that the X-ray steep, narrow H_beta, quasars
systematically show larger amplitude variations than the X-ray flat broad
H_beta quasars on timescales from 2 days to 20 days. On longer timescales we do
not find significant differences between steep and flat quasars, although the
statistics are poorer. We suggest that the above correlation between
variability properties and spectral steepness can be explained in a scenario in
which the X-ray steep, narrow line objects are in a higher L/L_Edd state with
respect to the X-ray flat, broad line objects. We evaluated the power spectrum
of PG1440+356 (the brigthest quasar in our sample) between 2E-7 and 1E-3 Hz,
where it goes into the noise. The power spectrum is roughly consistent with a
1/f law between 1E-3 and 2E-6 Hz. Below this frequency it flattens
significantly.

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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: mtrl-th
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The categories of this paper are: math
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: plasm-ph