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IAUC 5161: X-RAY TRANSIENT IN Mus (GRS 1121-68 = GS 1124-683)

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                                                  Circular No. 5161
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

X-RAY TRANSIENT IN MUSCA (GRS 1121-68 = GS 1124-683)
     N. Lund and S. Brandt, on behalf of the WATCH/Granat Team
(Danish Space 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.

1991 January 11                (5161)             Daniel W. E. Green

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