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IAUC 6467: gamma-RAY BURST; CAL 83

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                                                  Circular No. 6467
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)


gamma-RAY BURST
     L. Piro, E. Costa, M. Feroci, and M. Cinti, Istituto
Astrofisica Spaziale, CNR, Frascati; F. Frontera, D. Dal Fiume, M.
Orlandini, and G. Pizzichini, Istituto Tecnologie e Studio delle
Radiazioni Extraterrestri, CNR, Bologna; J. Heise and R. Jager,
Space Research Organization of the Netherlands (SRON), Utrecht; and
H. Muller, Beppo-SAX Scientific Data Center, Rome, communicate: "On
July 20.48395 UT, a gamma-ray burst was simultaneously detected in
the gamma-ray-burst monitor (GRBM, 60-600 keV) and one of the wide-
field-camera x-ray detectors (WFC, 2-30 keV) aboard Beppo-SAX.  The
burst had a peak flux of about 1200 counts/s (2 photons cmE-2 sE-1)
in the GRBM, and 90 counts/s (about 10E-8 erg cmE-2 sE-1) in the
WFC, with a fluence ratio F(2-30 keV)/F(60-600 keV) of about 0.02.
The WFC provided an image of the field with a resolution of 5'
(FWHM).  We conservatively estimate a maximum error-box radius of
10', corresponding to the maximum systematic deviation currently
found in position reconstruction.  The burst position is R.A. =
17h29m36s, Decl. = +49o02'.2 (equinox 2000.0).  It will be possible
to refine the position to a 2'.5 error-box radius after the
systematic residuals are calibrated.  This position lies within
0.25 deg of the center of the 2-deg error box of a simultaneous
BATSE event (trigger #5545, BATSE team, private comm.).  A search
from all catalogues available via several on-line services for
objects within the Beppo-SAX error box yielded no results.  The
Palomar digitized plates show several sources in the error box, but
no one of these is characterized by peculiar colors."


CAL 83
     P. Kahabka, University of Amsterdam; F. Haberl, Max-Planck-
Institut fur Extraterrestrische Physik, Garching; and A. N. Parmar,
Astrophysics Division, ESTEC, European Space Agency, report:  "The
supersoft x-ray source CAL 83 has been detected again at a
countrate of 0.21 +/- 0.04 count/s during a ROSAT/HRI target-of-
opportunity observation on Aug. 6.17 UT.  The duration of the x-ray
off-state on Apr. 28 (IAUC 6432) is limited to < 100 days.  This
constrains the mass of the white dwarf to >/= 1.1 solar masses if
the off/on behavior is due to an expanding/contracting white-dwarf
envelope without mass ejection (cf. Kahabka 1996, in Supersoft X-
Ray Sources, ed. J. Greiner, LNP 472, Springer, p. 215)."

                      (C) Copyright 1996 CBAT
1996 September 3               (6467)            Daniel W. E. Green

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