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Astron. Astrophys. 357, L57-L60 (2000)

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Letter to the Editor

A bright X-ray transient towards NGC 5128 (Centaurus A) *

H. Steinle, K. Dennerl and J. Englhauser

Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany (hcs@mpe.mpg.de)

Received 29 March 2000 / Accepted 19 April 2000


During five ROSAT HRI observations in July 1995, a bright X-ray source (designated 1RXH J132519.8-430312) was detected [FORMULA] south-west of the nucleus of NGC 5128 (Centaurus A) at the outer regions of the elliptical galaxy. At that time it was the brightest point source in the ROSAT HRI field-of-view. All other ROSAT observations made before and after these observations show no trace of the source suggesting that this is a highly variable object. Chandra observations of Cen A made in September 1999 show a source at the ROSAT position which may be the quiescent counterpart of the transient. It is very probable that the transient is located in NGC 5128. Given the existence of a transient source that close to the direction of NGC 5128, all observations (at least in soft X-rays) of Cen A, with instruments of low spatial resolution, must take the presence and variability of this object into account.

Key words: stars: novae, cataclysmic variables – stars: variables: general – galaxies: individual: NGC 5128 – galaxies: individual: Centaurus A – X-rays: galaxies – X-rays: stars

* Based in part on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: H. Steinle

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000