Soft X-ray spectral variations of the narrow line Seyfert 1 galaxy Markarian 766

Abstract

The X-ray variability of the narrow line Seyfert 1 galaxy Markarian 766 is studied using 9 ROSAT PSPC datasets. The spectrum is well described by a power law combined with a blackbody (kT~ 70 eV) soft excess. Examination of flux ratio changes and variability amplitude in 3 X-ray bands, shows that the power law component varies continuously on time-scales of ~5000s and is steeper when it is brighter. In contrast, variability of the soft excess is not detected. Spectral modeling of 31 spectra from different observations and at a range of count rates is also consistent with a picture in which the power law is steeper when it is brighter, and in which the soft excess component does not vary. The power law variability can be explained if the power law is produced by variable thermal or non-thermal Comptonization of soft photons. This behaviour is similar to that of Galactic black hole candidates in the low state. The X-ray and multiwavelength properties of Markarian 766 are shown to be very similar to those of other narrow line Seyfert 1s. This may mean that the rapid X-ray variability seen in other narrow line Seyfert 1s may also not originate in their strong soft excess components.

23 pages, LaTeX file plus 14 eps figures, needs mn.sty. MNRAS in press. Also available from http://www.ifca.unican.es/~carreraf/preprints.html

References in corpus (4)

• ASCA observations of Seyfert 1 galaxies: II. Relativistic Iron K-alpha emission
• On the Spectral Slopes of Hard X-ray Emission from Black Hole Candidates
• Extreme X-ray Variability In The Narrow-Line QSO PHL 1092
• The X-Ray Spectral Variability of Mrk 766

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