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Astron. Astrophys. 356, L17-L20 (2000)

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Letter to the Editor

ROSAT HRI monitoring of X-ray variability in the NLS1 galaxy PKS 0558-504

M. Gliozzi 1, Th. Boller 1, W. Brinkmann 1 and W.N. Brandt 2

1 Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany
2 The Pennsylvania State University, Department of Astronomy & Astrophysics, 525 Davey Lab, University Park, PA 16802, USA

Received 8 February 2000 / Accepted 2 March 2000


We present the results of ROSAT High Resolution Imager (HRI) observations and the survey data of the radio-loud Narrow-Line Seyfert 1 galaxy (NLS1) PKS 0558-504. We find strong and persistent X-ray variability on both short and medium time-scales. The most extreme amplitude variations require a radiative efficiency exceeding the theoretical maximum for a Schwarzschild black hole, suggesting the presence of a rotating black hole or the influence of relativistic beaming effects. The spatial analysis rules out the possibility that the high luminosity and the strong variability are related to a nearby source.

Key words: galaxies: active – galaxies: ISM – galaxies: fundamental parameters – galaxies: nuclei – X-rays: galaxies

Send offprint requests to: mgliozzi@xray.mpe.mpg.de

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© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000