Exite2 Observation of the Sigma Source Grs 1227+025

Abstract

We report the second-generation Energetic X-Ray Imaging Telescope Experiment (EXITE2) hard X-ray imaging of the sky around 3C 273. A 2 hr observation on 1997 May 8 shows a similar to260 mcrab source detected at similar to4 sigma in each of two bands (50-70 and 70-93 keV) and located similar to30' from 3C 273 and consistent in position with the Granat SIGMA source GRS 1227+025. The EXITE2 spectrum is consistent with a power law with photon index 3 and large low-energy absorption, as indicated by the SIGMA results. No source was detected in more sensitive follow-up EXITE2 observations in 2000 and 2001 with 3 sigma upper limits of 190 and 65 mcrab, respectively. Comparison with the flux detected by SIGMA shows the source to be highly variable, suggesting it may be nonthermal and beamed and thus the first example of a "type 2'' (absorbed) blazar. Alternatively, it might be an unprecedented very highly absorbed binary system undergoing accretion-disk instability outbursts, possibly either a magnetic cataclysmic variable or a black hole X-ray nova.