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An exploratory study of the hard X-ray variability properties of PG quasars with RXTE

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 Added by Thomas Boller
 Publication date 2000
  fields Physics
and research's language is English
 Authors M. Guainazzi




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We have monitored with the RXTE PCA the variability pattern of the 2-20 keV flux in four PG quasars (QSOs) from the Laor et al. (1994) sample. Six observations of each target at regular intervals of 1 day were performed. The sample comprises objects with extreme values of Balmer line width (and hence soft X-ray steepness) and spans about one order of magnitude in luminosity. The most robust result is that the variability amplitude decreases as energy increases. Several options for a possible ultimate driver of the soft and hard X-ray variability, such as the influx rate of Comptonizing relativistic particles, instabilities in the accretion flow or the number of X-ray active sites, are consistent with our results.



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114 - R. Bachev , D. Grupe , S. Boeva 2009
We present the results from a monitoring campaign of the Narrow-Line Seyfert~1 galaxy PG 1211+143. The object was monitored with ground-based facilities (UBVRI photometry; from February to July, 2007) and with Swift (X-ray photometry/spectroscopy and UV/Optical photometry; between March and May, 2007). We found PG 1211+143 in a historical low X-ray flux state at the beginning of the Swift monitoring campaign in March 2007. It is seen from the light curves that while violently variable in X-rays, the quasar shows little variations in optical/UV bands. The X-ray spectrum in the low state is similar to other Narrow-Line Seyfert 1 galaxies during their low-states and can be explained by a strong partial covering absorber or by X-ray reflection onto the disk. With the current data set, however, it is not possible to distinguish between both scenarios. The interband cross-correlation functions indicate a possible reprocessing of the X-rays into the longer wavelengths, consistent with the idea of a thin accretion disk, powering the quasar. The time lags between the X-ray and the optical/UV light curves, ranging from ~2 to ~18 days for the different wavebands, scale approximately as ~lambda^(4/3), but appear to be somewhat larger than expected for this object, taking into account its accretion disk parameters. Possible implications for the location of the X-ray irradiating source are discussed.
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130 - F. DAmico 2001
We report RXTE results of spectral analyses of three (Sco X-1, GX 349+2, and Cyg X-2) out of the 6 known Z sources, with emphasis in the hard X-ray emission. No hard X-ray tails were found for Cyg X-2 (< 8.4E-5 photons cm**-2 s**-1, 50-100 keV, 3 sigma) and for GX 349+2 (< 7.9E-5 photons cm**-2 s**-1, 50-100 keV, 3 sigma). For Sco X-1 a variable hard X-ray tail (with an average flux of 2.0E-3 photons cm**-2 s**-1, 50-100 keV) has already been reported. We compare our results to reported detections of a hard component in the spectrum of Cyg X-2 and GX 349+2. We argue that, taking into account all the results on detections of hard X-ray tails in Sco X-1 and GX 349+2, the appearance of such a component is correlated with the brightness of the thermal component.
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