Central Bureau for Astronomical Telegrams
IAUC 5032: GALACTIC CENTER; 1990I
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Circular No. 5032
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
GALACTIC CENTER
P. Mandrou, Centre d'Etude Spatiale des Rayonnements, Toulouse,
communicates on behalf of the Granat Team (cf. IAUC 5017): "A
sequence of observations of the Galactic Center region in the medium/
hard x-ray and soft gamma-ray regions was obtained with the ART-P
and SIGMA telescopes aboard the Granat space observatory on Mar. 24,
Apr. 4, 8, 12, and 17. Preliminary analysis of ART-P data in the 4-
to 30-keV band has revealed the presence of six sources in a 1.5 deg
x 1.5 deg field centered at the Galactic Center. Among them are
1E 1740.7-2942, SLX 1744-299, A1742-294, and 1E 1743.1-2843. SIGMA
telescope data show that, at energies above 30 keV, the radiation
from 1E 1740.7-2942, detected up to about 300 keV, strongly dominates
the overall emission from this region. Two sources have been
resolved by the ART-P telescope in the 20' central region: Sgr A and
a second source, 10' distant, whose position coincides within errors
with 1E 1741.7-2850, previously detected by the Einstein satellite
in the 0.9- to 4-keV band. Further observations of these sources are
strongly urged. A previously unknown source, GRS 1758-258 (GRanat
Source), with a very hard spectrum, has been discovered by both ART-P
and SIGMA telescopes within a 2' radius error circle centered at R.A.
= 17h57m.9, Decl. = -25 47'.4 (equinox 1950.0), i.e., 20' from GX 5-1.
Preliminary analysis of ART-P data yields flux estimates of 40 +/- 8
mCrab and 90 +/- 20 mCrab, respectively, in the 10- to 20-keV and 20-
to 40-keV bands. Preliminary analysis of SIGMA data in the 40- to
120-keV energy range suggests that most of the hard radiation
previously imputed to GX 5-1 actually originates from the nearby hard
source GRS 1758-258."
SUPERNOVA 1990I IN NGC 4650A
M. M. Phillips, Cerro Tololo Interamerican Observatory, telexes:
"Spectra of SN 1990I in NGC 4650A obtained on May 18, June 7, and
June 8 UT with the Cerro Tololo 1.5-m telescope indicate that this
object is a type-Ib (rather than type-Ia) supernova (cf. IAUC 5003).
The May 18 spectrum resembles those of the helium-strong type-Ib SNe
1983N and 1984L approximately 15-20 days past maximum. Weak [Ca II]
729.1- and 732.4-nm emission was detected in the June 8 spectrum,
indicating that the transition to the supernebular phase has begun.
Narrow H-alpha and H-beta emission is observed superposed on the
supernova spectra, suggesting that this object may be associated
with an H II region."
1990 June 14 (5032) Daniel W. E. Green
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