The X-ray spectrum of the superluminal quasar 1928+73.

Abstract

EXOSAT observations (0.1-10 keV) of the radio-loud quasar 1928+73, which displays superluminal motion, were made at four epochs between 1983/283 and 1984/009, and we obtained spectra of this source from the EXOSAT database. The X-ray spectrum (0.1-10 keV) can be explained by a power law and uniform absorption model. No significant low-energy absorption or soil excess were detected. Both soil (0.1-2 keV) and hard (2-10 keV) X-ray flux variations of this quasar were found on a time- scale of one month. Spectral index values obtained from the power-law model suggest that they exceed the `canonical' value. A thermal bremsstrahlung model also fits well. Uncorrelated variations of the soil and hard fluxes have been found in this source which indicate that they have different origins. A soil excess is apparent when the spectra are fitted with a canonical photon index ~1.7. The Spectra presented here are the first in the X-ray region for 1928+73.