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Astron. Astrophys. 348, 678-684 (1999)

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An ASCA observation of the radio-loud narrow-line Seyfert 1 galaxy RGB J0044+193

J. Siebert 1,2, K.M. Leighly 3, S.A. Laurent-Muehleisen 4, W. Brinkmann 1, Th. Boller 1 and M. Matsuoka 2

1 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85740 Garching, Germany
2 Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-01, Japan
3 Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
4 IGPP/LLNL, 7000 East Av., Livermore, CA 94550, USA

Received 3 November 1998 / Accepted 24 February 1999


Narrow-line Seyfert 1 galaxies are generally found to be radio-quiet and there was only one radio-loud object known so far (PKS 0558-504). Here we present the results of a 50 ksec ASCA observation of the recently discovered second radio-loud NLS1 galaxy RGB J0044+193. The X-ray data are complemented by radio observations and a new optical spectrum for this source.

We find evidence for variable radio emission and an inverted radio spectrum of RGB J0044+193. The optical continuum turned out to be extremely blue. This may either indicate additional line emission, for example from Fe I, or scattering of a blue intrinsic continuum. The X-ray spectrum shows a clear break around 1.8 keV. Above this energy the spectrum is characterized by a power law with a photon index of [FORMULA]. For energies below 2 keV the spectrum is much softer and it can either be modeled with a steeper power law ([FORMULA]) or a blackbody component with a temperature around 0.2 keV. The X-ray count rate of the source decreased by a factor of two within one day and there is evidence for low amplitude variability on much shorter time scales. Given its average 2-10 keV X-ray luminosity of [FORMULA] erg s-1, RGB J0044+193 is significantly more variable than a typical broad line Seyfert 1 galaxy of comparable X-ray luminosity, but consistent with the bulk of NLS1 galaxies.

The spectral as well as the variability properties of RGB J0044+193 are indistinguishable from those of radio-quiet NLS1s. In particular, we find no evidence for a flat X-ray component due to inverse Compton emission related to the putative non-thermal radio emission from RGB J0044+193. We argue, however, that this does not rule out a pole-on orientation for RGB J0044+193.

Key words: galaxies: abundances – galaxies: individual: RGB J0044+193 – radio lines: general – X-rays: general

Correspondence to: J. Siebert (jos@mpe.mpg.de)

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199