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Astron. Astrophys. 356, 11-22 (2000)

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The enigmatic soft X-ray AGN RX J0134.2-4258 *

D. Grupe 1, K.M. Leighly 2, H.-C. Thomas 3 and S.A. Laurent-Muehleisen 4

1 MPI für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
2 Columbia Astrophysics Laboratory, 550 West 120th St., New York, NY 10027, USA
3 MPI für Astrophysik, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
4 UC-Davis and IGPP/LLNL, 7000 East Av., Livermore, CA 94550, USA

Received 8 June 1999 / Accepted 12 January 2000


We report the discovery and analysis of the follow-up ROSAT pointed observation, an ASCA observation and optical and radio observations of the enigmatic soft X-ray AGN RX J0134.2-4258. In the optical, RX J0134.2-4258 appears as an extreme `Narrow-Line Seyfert 1 galaxy' (NLS1), with very strong FeII emission, very blue optical continuum spectrum and almost no Narrow Line Region emission. While its spectrum was one of the softest observed from an AGN during the ROSAT All-Sky Survey, its spectrum was found to be dramatically harder during a pointed observation although the count rate remained constant. We found in the pointed observation that the spectrum is softer when it is fainter and spectral fitting demonstrates that it is the hard component that is variable. The ASCA observation confirms the presence of a hard X-ray power law, the slope of which is rather flat compared with other NLS1s. Survey and followup radio observations reveal that RX J0134.2-4258 is also unusual in that it is a member of the rare class of radio-loud NLS1s, and, with R=71, it holds the current record for largest radio-to-optical ratio in NLS1s. We discuss possible scenarios to explain its strange behaviour.

Key words: acceleration of particles – galaxies: active – galaxies: nuclei – galaxies: quasars: individual: RX J0134.2 – 4258

* Based in part on observations at the European Southern Observatory La Silla (Chile) with the 2.2m telescope of the Max-Planck-Society during MPG and ESO time, and with the ESO 1.5m telescope in September/October 1995

Send offprint requests to: D. Grupe (dgrupe@xray.mpe.mpg.de)

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© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000