Circular No. 6687
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)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
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Phone 617-495-7244/7440/7444 (for emergency use only)


GRB 970616
     K. Hurley, Space Sciences Laboratory, University of California at
Berkeley (UCB); C. Kouveliotou, Universities Space Research Association at
Marshall Space Flight Center; and F. Marshall, Goddard Space Flight Center,
on behalf of large interplanetary network (IPN), BATSE and XTE teams,
report a refined error box for this source, based on triangulation of
the almost-final Ulysses and BATSE data, as well as XTE data reported on
IAUC 6683.  The IPN annulus, determined from the Ulysses-BATSE time
difference, has a radius of 49.813 deg, is centered at R.A. = 22h10m30s,
Decl. = -27d25'.0 (equinox 2000.0) and has a full width of 2'.2.  The
intersection of this annulus with the XTE error region has corners at
R.A. = 1h19m36s, Decl. = -5d42'.0; 1h19m36s, -5d46'.3; 1h18m23s,
-5d12'.4 and 1h18m17s, -5d14'.4.  The optical and x-ray sources described
below lie within this error box.

     T. Murakami, R. Fujimoto, Y. Ueda and R. Shibata, Institute of Space
and Astronautical Science, Kanagawa, report, on behalf of a large
international collaboration: "We observed the XTE/IPN error box of
GRB 970616 (IAUC 6683) with ASCA during June 20.15-21.44 UT for a net
total of 50 ks.  Four x-ray sources are detected in the ASCA SIS field of
view at the following positions: R.A. = 1h18m48s, Decl. = -5d26'.3; 1h18m42s,
-5d27'.1; 1h18m39s, -5d18'.3 and 1h18m35s, -5d19'.8 (equinox 2000.0, error
radius 1').  The first and the fourth source error regions are entirely
inside the refined IPN annulus reported above; the third source is slightly
and the second is entirely outside the annulus.  Their average SIS countrates
at 0.7-7 keV are 3.0, 3.3, 1.6 and 1.6 counts/ks, respectively
(1 count/ks roughly corresponding to 2.3 x 10**-14 erg cm-2 s-1 at 2-7 keV
for a Crab-like spectrum).  The first source appears to be variable, its
countrate decreasing by a factor of two from the first to the second
half of the observation."

     T. Galama, University of Amsterdam (UoA); K. Hurley, T. Broadhurst
and B. Frye, UCB; and J. van Paradijs, UoA and University of Alabama
at Huntsville, report, on behalf of a large international collaboration:
"We have made R-band images of the error box of GRB 970616 with
Keck II on June 21.61, 23.59 and 24.61 UT.  We find a variable
object 3".2 east and 3".6 north of a relatively bright object
located at R.A. = 1h18m55s.7, Decl. = -5d27'23" (equinox 2000.0; position
inferred from the Digital Sky Survey).  A preliminary differential
analysis shows that between the first and third observations the object
faded by 1.5 +/- 0.2 mag to roughly mag 24.  This variable is inside the
refined IPN/XTE error box above but lies about 2' from the best position
of the variable ASCA source."

                      (C) Copyright 1997 CBAT
1997 June 25                   (6687)              Brian G. Marsden