Central Bureau for Astronomical Telegrams
IAUC 6901: 1998bw; OGLE-2 SYSTEM FOR MICROLENSING EVENTS
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Circular No. 6901
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1998bw IN ESO 184-G82
E. M. Sadler, University of Sydney; R. A. Stathakis and B. J.
Boyle, Anglo-Australian Observatory; and R. D. Ekers, Australia
Telescope National Facility, report: "The spectrum of the variable
object in ESO 184-G82 (IAUC 6895, 6896, 6899) closely resembles the
pre-maximum spectrum of the type-Ib supernova 1983N (Richtler
and Sadler 1983, A.Ap. 128, L3). The detection of prompt radio
emission (IAUC 6896; see
http://www.narrabri.atnf.csiro.au/public/grb for more recent data)
is also typical of type-Ib supernovae (though this object is about
30 times more luminous at radio wavelengths than was SN 1983N). It
therefore seems certain that the object in ESO 184-G82 is a
supernova discovered before maximum light. The optical lightcurve
(IAUC 6895, 6899) implies that the supernova explosion probably
occurred sometime during Apr. 21-27 -- i.e., consistent with the
supernova and the gamma-ray burst GRB 980425 occurring
simultaneously. We suggest that the two events are associated, and
that we may be seeing a supernova in which the core has collapsed
to a black hole (plus accretion disk) rather than a neutron star,
after models proposed by Woosley (1993, Ap.J. 405, 273) and
Paczynski (1998, Ap.J. 484, L45)."
OGLE-2 SYSTEM FOR MICROLENSING EVENTS
A. Udalski and M. Szymanski, on behalf of the OGLE
collaboration, announce: "The Early Warning System (EWS) designed
for the detection of microlensing events in progress and
successfully implemented during the first phase of the OGLE
experiment (cf. IAUC 5997, 6164, 6177) has been reinstalled for the
second phase of the experiment. About 25 million stars are
currently monitored in the Galactic bulge each night with the 1.3-m
Warsaw telescope at Las Campanas Observatory. The expected rate of
microlensing events is about 50 per observing season (based on
preliminary results from the 1997 season). So far in the 1998
season, 16 microlensing event candidates have been detected, five
of them still in their early phases before or shortly after maximum
light. We direct attention to the event OGLE-1998-BUL-14, which is
expected to reach high amplification with maximum around May 20 and
be brighter than I = 15. Finding charts, photometry, and other
information about OGLE events can be found at
http://www.astrouw.edu.pl/~ftp/ogle or
ftp://sirius.astrouw.edu.pl/ogle/ogle2/ews. Astronomers interested
in follow-up observations and who wish to receive e-mail
notification should send a request to ogle-ews@sirius.astrouw.edu.pl."
(C) Copyright 1998 CBAT
1998 May 13 (6901) Daniel W. E. Green
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