The enigmatic Soft X-ray AGN RX J0134.2--4258

TL;DR

This paper reports the discovery and multi-wavelength analysis of RX J0134.2-4258, an unusual radio-loud Narrow-Line Seyfert 1 galaxy with variable X-ray spectra and extreme optical properties, challenging existing models of AGN behavior.

Contribution

It provides the first detailed multi-wavelength study of a rare radio-loud NLS1 with variable X-ray spectra and extreme optical features, highlighting its unique properties.

Findings

RX J0134.2-4258 is a radio-loud NLS1 with the highest known radio-to-optical ratio.

The X-ray spectrum varies from very soft to hard, with the hard component being variable.

The galaxy exhibits extreme optical features, including strong FeII emission and a blue continuum.

Abstract

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.