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IAUC 5140: GALACTIC CENTER; 1951J, 1953J,, 1954ac

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                                                  Circular No. 5140
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

     The SIGMA/GRANAT team (P. Mandrou and J. P. Roques, Centre
d'Etude Spatiale des Rayonnements; R. Sunyaev and E. Churazov, Space
Research Institute, Moscow; and J. Paul and B. Cordier, Service
d'Astrophysique, C.E.A., Saclay) communicate:  "We report on a
remarkable 14-hr observation of the x-ray source 1E 1740.7-2942 during
Oct. 13-14, in the course of intensive observations of the Galactic
Center region by the SIGMA telescope aboard the GRANAT observatory.
This object, not detected above 200-300 keV by the SIGMA telescope
during five previous observations in March-April (IAUC 5032) and
September-October, was found to exhibit suddenly a highly significant
feature, up to about 800-keV on Oct. 13-14.  If we compare this
high-energy emission to a power-law extrapolation from the 35- to
200-keV data, it appears as a 250- to 600-keV shoulder, reaching a
flux of about 7 x 10E-6 photons cmE-2 sE-1 keVE-1, with a significance
level > 6 sigma.  Compared to the previous observations, however,
the 35- to 200-keV energy domain of the spectrum showed during
this transition no significant variations in shape and intensity.
Also the 4- to 30-keV flux, measured by the Soviet x-ray telescope
ART-P during the same period, did not show significant changes.  The
feature was not significantly detected during an Oct. 18 observation
of this source, and the spectrum of 1E 1740.7-2942 was found to be
in its 'normal state'.  The object exhibits strong variability above
300 keV, with corresponding changes from a 'normal' to a 'high'
state on a time scale of typically one day."

SUPERNOVAE 1951J, 1953J, AND 1954ac
     J. Mueller reports her discovery of three supernovae on prints
from the first Palomar Sky Survey; the 1951 exposures were taken by
A. Wilson, the other exposures by G. Abell.  SN 1951J in UGC 3331
(R.A. = 5h35m.3, Decl. = +0 05', equinox 1950.0) was at mag about
17.5 on the 1951 Nov. 29 plate; the object was 23".5 west and 13".4
north of the galaxy nucleus.  SN 1953J in UGC 472 (R.A. = 0h42m.3,
Decl. = +16 40', equinox 1950.0) was at mag about 17.5 on the 1953
Dec. 31 photograph, and was 15" east and 5" south of the galaxy
nucleus.  SN 1954ac in UGC 465 (R.A. = 0h41m.1, Decl. = +32 35',
equinox 1950.0) appears at mag 18 on a 1954 Oct. 4 plate, located
3".4 east and 40".3 south of the galaxy's center.  Palomar 1.5-m
telescope CCD frames obtained by G. Carlson show no object currently
present at the locations of SNe 1953J and 1954ac.

1990 November 29               (5140)             Daniel W. E. Green

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