Central Bureau for Astronomical Telegrams
IAUC 6939: GRB 980613; MICROLENSING EVENT
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Circular No. 6939
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
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Phone 617-495-7244/7440/7444 (for emergency use only)
GRB 980613
E. Costa, Istituto di Astrofisica Spaziale, CNR, Rome; L. A.
Antonelli, Osservatorio Astronomico di Roma and BeppoSAX, Rome; C.
De Libero, G. Spoliti, M. Celidonio, A. Tesseri, and M. R. Daniele,
BeppoSAX, Rome; J. in 't Zand, Space Research Organization
Netherlands, Utrecht; and F. Frontera, Istituto Tecnologie e Studio
Radiazioni Extraterrestri, CNR, Bologna, report: "The error circle
of GRB 980613 (IAUC 6938) was observed with the BeppoSAX Narrow
Field Instruments from June 13.5618 (9 hr after the burst) to
14.6771 UT. Two previously unknown sources have been detected by
the Medium Energy Concentrator Spectrometer (MECS) within the
circle during this follow-up observation. One source, 1SAX
J1018.1+7133, is located at R.A. = 10h18m04s, Decl. = +71o33'30"
(equinox 2000.0; error radius 50"), and the other source, 1SAX
J1017.9+7127, is located at R.A. = 10h17m53s, Decl. = +71o27'24".
1SAX J1018.1+7133 has an average count rate of 0.0036 +/- 0.0004
counts/s in the two MECS units, corresponding to a flux of (1.9 +/-
0.2) x 10E-13 erg cmE-2 sE-1. This source does not show
substantial variability. 1SAX J1017.9+7127 has an average count
rate of 0.0016 +/- 0.0004 counts/s in the two MECS units,
corresponding to a flux of (1.1 +/- 0.3) x 10E-13 erg cmE-2 sE-1.
In the first 7000 s, the average count rate is about 3 times this
value; due to this fading behavior, the source is likely to be the
x-ray afterglow of GRB 980613."
MICROLENSING EVENT
D. Bennett, University of Notre Dame, reports for the MACHO
Collaboration (cf. IAUC 6845) plus affiliate S. Rhie: "Further
observations of microlensing event MACHO-98-SMC-1 (cf. IAUC 6935)
with the Mount Stromlo 1.3-m MACHO survey telescope and the Cerro
Tololo 0.9-m telescope confirm the binary-lens interpretation and
yield a prediction for the time of the second caustic crossing of
June 19.2 +/- 1.5 UT. Photometric measurements are urgently
requested because the crossing timescale will indicate whether this
binary lens resides in the Small Magellanic Cloud (with the star
then expected to reach R about 18 at the peak of a about 12-24-hr
crossing) or in the Milky Way's dark halo (with expected R < 17 at
the peak of a about 1-hr crossing). Potential observers are urged
to contact the MACHO team (see IAUC 6935) to coordinate
observations. For additional information and updates on this event,
see http://darkstar.astro.washington.edu/98-SMC-1_lev2.html and
http://bustard.phys.nd.edu/MPS/98-SMC-1/."
(C) Copyright 1998 CBAT
1998 June 16 (6939) Daniel W. E. Green
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