A BBXRT Observation of the High-Luminosity Quasar H1821+643

Abstract

We present the results of an observation of the high-luminosity quasar H1821+643 with the Broad-Band X-Ray Telescope (BBXRT) performed in 1990 December. The 2-10 keV flux and power-law spectral index are found to be consistent with previous values obtained by EXOSAT and Ginga which indicates that the medium-energy continuum has remained steady for at least 6.5 yr. Contrasting with this is the result that the Fe Kα line present in Ginga observations of this source (observed equivalent width 210±80 eV) is not detected by BBXRT. We estimate that a narrow iron line, if it had been present during the BBXRT observation at the same strength as it was in the Ginga observations, should have been detected with a probability of 88%. We argue against variability of the line between the BBXRT and Ginga observations and suggest the possibility that the line is broad.