Central Bureau for Astronomical Telegrams
IAUC 5655: GALACTIC CENTER; N Pup 1991
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Circular No. 5655
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@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
GALACTIC CENTER
I. F. Mirabel, Service d'Astrophysique, Centre d'Etudes de
Saclay; L.F. Rodriguez, Universidad Nacional Autonoma de Mexico;
and B. Cordier, J. Paul, and F. Lebrun, Service d'Astrophysique,
Centre d'Etudes de Saclay, communicate: "In coordination with
SIGMA, we are carring out Very Large Array (VLA) radio observations
of 1E 1740.7-2942 and GRS 1758-258, the two strongest persistent
soft gamma-ray sources in the galactic center region. Within the
SIGMA error box for GRS 1758-258, there is a radio source that has
shown a flux variation in the same sense as the 40- to 150-keV
photon counts of SIGMA. In 1992 January-April, the 6-cm flux from
this source was below our detection limit of 0.07 mJy. On Sept. 10
it appeared with a flux of 0.48 +/- 0.05 mJy, and on Sept. 26 it
had a flux of 0.58 +/- 0.06 mJy. A similar trend was observed by
SIGMA in soft gamma-rays, since GRS 1758-258 was not detected
during 1992 February-April above the 1-sigma detection limit of 8
mCrab, whereas in 1992 September it reappeared with a 40- to 150-
keV flux of 35 +/- 12 mCrab (Cordier et al., Compton Symp. 1992).
This time-variable radio source is likely to be the radio
counterpart of GRS 1758-258. Its position on Sept. 10 was R.A. =
17h58m06s.3, Decl. = -25 44'34".0 +/- 2" (equinox 1950.0), which is
at the center of the double-sided radio jets reported by Rodriguez,
Mirabel, and Marti (1992, Ap.J. 401, L15)."
I. F. Mirabel and P. A. Duc, Service d'Astrophysique, Centre
d'Etudes de Saclay, report: "We are searching for infrared counterparts
of 1E 1740.7-2942 and GRS 1758-258 with the 2.2-m telescope
of the European Southern Observatory. H, J, and K images taken on
June 16 and 17 reveal no infrared counterparts down to mag K = 17
within 2" of the VLA compact variable radio sources associated with
the soft gamma-ray sources. For 1E 1740.7-2942 our result is
comparable to that obtained by Prince and Skinner (IAUC 5252), and
more recently by Djorgovski et al. (IAUC 5596) on 1992 July 21. If
the optical absorption to these sources is < 50 mag, the magnitude
limits at 2.2 microns imply that the binary companions of these
black-hole candidates are not massive stars with optical
luminosities brighter than Mv = -3 (as in Cygnus X-1)."
NOVA PUPPIS 1991
Photometry (+/- 0.02) by A. C. Gilmore, Mount John University
Observatory (cf. IAUC 5628): Oct. 15.64 UT, V = 11.94, B-V =
+0.02, U-B = -1.11, V-R = +0.38.
1992 November 18 (5655) Daniel W. E. Green
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