Circular No. 5398
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
     R. Sunyaev, E. Churazov, F. Lebrun, and D. Barret, on behalf of
the Granat team (Space Research Institute, Moscow; Centre d'Etude
Spatiale des Rayonnements, Toulouse; Service d'Astrophysique du CEN,
Saclay), communicate:  "A set of seven Granat/SIGMA observations
made during Oct. 1-18 yielded positive detection of 1E 1740.7-2942
with a 100- to 300-keV flux of about 48 mCrab (i.e., about 2-3 times
lower than the average value observed in this band by SIGMA in
1990).  The source spectrum was hard, with evidence of excess above
200 keV.  The peak at 4 standard deviations is clearly seen on the
250- to 600-keV image at a position compatible with that of 1E
1740.7-2942.  This result indicates that the spectrum became signif-
icantly harder than when the object was observed in its low state
earlier in 1991 (IAUC 5204).  In four subsequent sessions during
Oct. 15-20, the ART-P telescope detected the source in the standard
x-ray band with an average 3- to 20-keV flux of 12 mCrab.  In the
data averaged over previous observations from Aug. 30 to Sept. 23,
the source was not detected, with upper limits (3 sigma) on the
average flux of about 5 mCrab at 3-20 keV and about 14 mCrab at
40-300 keV."
 
 
NOVA MUSCAE 1991
     R. Sunyaev, M. Gilfanov, F. Lebrun, and D. Barret, on behalf of
the Granat team (Space Research Institute, Moscow; Centre d'Etude
Spatiale des Rayonnements, Toulouse; Service d'Astrophysique du CEN,
Saclay), report:  "On Oct. 22-23 and 26-27, Granat observed N Mus
1991.  No x-ray flux was detected from this source in the 35- to
250-keV SIGMA band, with an upper limit (3 sigma) of about 22 mCrab
(i.e., at least 4 times below that previously observed on Aug. 14;
cf. IAUC 5329).  ART-P observations on Oct. 26 gave an upper limit
(3 sigma) on the 6- to 30-keV flux at 4 mCrab (9 times below the
Aug. 14 level)."
 
 
COMET SHOEMAKER-LEVY (1991d)
     Total visual magnitude estimates (cf. IAUC 5379):  Nov. 12.56
UT, 10.7 (C. S. Morris, Pine Mountain Club, CA, 0.26-m reflector);
17.52, 11.8 (A. Hale, Las Cruces, NM, 0.41-m reflector); Dec. 4.18,
11.2 (H. Mikuz, Ljubljana, Yugoslavia, 0.20-m reflector); 5.51,
11.7 (Hale).
 
 
1991 December 5                                   Daniel W. E. Green