Is PKS 2155 an extragalactic source?

Abstract

The X-ray source H2155-304, identified with the radio source PKS 2155 and with a 14 mag star-like object, is commonly believed to be a BL Lac object on the basis of the blue featureless continuum, the presence of optical polarization, and the violent variability (m_B varies from 12.8 to 14.2 on a time scale of months). This paper presents observations of this source in the far ultraviolet (1200-3000 A) obtained with the IUE. The presence of weak variable emission features is discussed, and the extragalactic nature of the object is questioned.