Castro-Tirado, A. J.3; Brandt, Søren1; Lund, Niels1; Cameron, R. A.3; Grove, J. E.3; Kroeger, R. A.3
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 unknown
A. J. Castro-Tirado, S. Brandt, and N. Lund, Granat WATCH team (Danish Space Research Institute, Lyngby; and Space Research Institute, Moscow), report: "The hard x-ray transient reported by Paciesas et al. on IAUC 5580 has been observed by the WATCH all-sky monitor on Granat. The source intensity above 20 keV was 2.5 Crab on Aug. 11.7 UT. The source has been localized to the following position: R.A. = 4h17m.5, Decl. = +33 30' (equinox 1950.0), with a probable error radius of 0.5 deg." R. A. Cameron, Universities Space Research Association; and J. E. Grove, R. A. Kroeger, W. N. Johnson, and J. D. Kurfess, Naval Research Laboratory; on behalf of the Compton Observatory OSSE team, report: "Preliminary analysis of the spectrum of the gamma-ray transient source GRO J0422+32 (IAUC 5580, 5584), derived from OSSE observations between Aug. 11.10 and 12.00 UT, shows the source to have a spectrum similar to, and three times brighter than, the black-hole candidate Cygnus X-1 as observed by OSSE in 1991 June. Significant emission is observed up to about 600 keV, with an average source flux of 1.8 photons cmE-2 sE-1 MeVE-1 at 100 keV. The continuum spectrum between 60 and 600 keV is not compatible with a single power law. The spectrum over this energy range is well represented by a two-temperature Sunyaev-Titarchuk comptonized plasma emission model (Sunyaev and Titarchuk 1980, A.Ap. 86, 121), with characteristic electron temperatures of 30 and 60 keV. The intensities of these two components are comparable at 100 keV and have optical depths of about 6 and 3, respectively. The OSSE instrument is also collecting event rate data in 8-ms samples on GRO J0422+32. Preliminary analysis of this timing data has shown no evidence for QPO behavior."
International Astronomical Union Circulars (iauc), 1992, Issue 5587