Lund, Niels1; Brandt, Søren1; Makino, F.3; McNaught, R. H.3; Jones, A.3; West, R. M.3
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 unknown
Research Institute, Lyngby; and Space Research Institute, Moscow), report: "A new x-ray source in Musca, GRS 1121-68, has been discovered in data obtained by the WATCH detectors on Jan. 9. The spectrum of the source was harder than that of the Crab nebula, and the flux was about twice that from the Crab and increasing slowly during the observation. The source remained at a constant intensity level on Jan. 10. On Jan. 5 this source was not bright enough to be detectable by WATCH. The preliminary position is R.A. = 11h21m, Decl. = -68.1 deg (equinox 1950.0; uncertainty about 1 deg). We have not found any catalogued hard x-ray sources within our error circle; however, close to the given position, we have noted the existence of a radio pulsar (at R.A. = 11h10m, Decl. = -69 deg) with a period of 0.8 s, and a gamma-ray burst source, GRB 820829B, detected by Venera 13/14 in 1982. We have not detected any strong pulsations from the new source, but the time resolution of the available data does not allow a search for pulsations with periods shorter than about 20 s." F. Makino and the Ginga Team, Institute of Space and Astronautical Science, telex: "A bright transient x-ray source, designated GS 1124-683, was discovered with the All Sky X-ray Monitor (ASM) aboard Ginga on Jan. 8. The position determined by combining the ASM position with the line position obtained by scanning with the Large Area Proportional Counters (LAC) is R.A. = 11h24m.6, Decl. = -68 18' (equinox 1950.0). The corners of the error box are 11h23m.9, -68 08'; 11h23m.7, -68 20'; 11h25m.4, -68 37'; and 11h25m.6, -68 16'. The x-ray flux was about 0.8 Crab on Jan. 8.8 UT and 2.2 Crab on Jan. 11.04, observed with the ASM and LAC, respectively. The spectrum was of power-law type with index of about -2.3. No pulsation was observed in the period range 0.12-30 s. Optical observation is urged." R. H. McNaught, University of Adelaide, reports that A. Jones, Nelson, N.Z., found nothing to mag about 10 in a visual search of the region on Jan. 11.4 UT. R. M. West, European Southern Observatory, reports that a 10-min GPO astrograph plate was taken as La Silla, showing no new object in the 2 x 2 deg field brighter than mag 7-8; a search plate will be taken with the Schmidt telescope at La Silla.
International Astronomical Union Circulars (iauc), 1991, Issue 5161