Central Bureau for Astronomical Telegrams
IAUC 6618: GALACTIC CENTER REGION; GRB 970228
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Circular No. 6618
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GALACTIC CENTER REGION
J. in 't Zand and J. Heise, Space Research Organization of the
Netherlands (SRON), Utrecht; A. Bazzano and P. Ubertini, Istituto
di Astrofisica Spaziale, CNR, Frascati, Italy; J. M. Muller and M.
Smith, SRON and BeppoSAX, Rome, report: "A 3-day exposure with
BeppoSAX Wide Field Camera 1 during Mar. 29-Apr. 1 of the galactic-
center field reveals the following preliminary results on four weak
sources, of which one is not catalogued. The previously unknown x-
ray source was detected at 8 mCrab (1.6-26 keV) on Mar. 29. Its
position is R.A. = 17h44m42s, Decl. = -29o16'.9 (equinox 2000.0),
with an error-circle radius of 3'; the source has been designated
1SAX J1744-2916. Another transient source was detected on Mar. 30
at R.A. = 17h45m46s, Decl. = -29o06'.3. The 3' error-circle radius
includes RX J17457-2904. The average intensity was 9 mCrab. The
5-sigma upper limits for these two sources, for each of the three
days when they were not detected, is 4 mCrab. The two transients
SAX J1750.8-2900 and GRS 1737-31 that were active one week eariler
(IAUC 6597, 6599, 6606) were not detected above a 5-sigma upper
limit of 2 mCrab for the whole observation period."
GRB 970228
B. Margon and E. W. Deutsch, University of Washington; and D.
Q. Lamb and F. J. Castander, University of Chicago, write:
"Observations with the Astrophysical Research Consortium's 3.5-m
telescope at Apache Point on Mar. 3.1 UT of the BeppoSAX WFC1 error
circle (IAUC 6572) show an object near the position of the extended
object reported by Groot et al. and Metzger et al. (IAUC 6588).
Using the astrometric positions of 7 stars (kindly provided by M.
Metzger) that lie within about 1' of the object, we have measured
the position of the object as R.A. = 5h01m46s.61 +/- 0s.020, Decl.
= +11o46'53".4 +/- 0".15 in the USNO A1.0 astrometric reference
frame. The position of the object thus lies within 0".3 of the
position of the extended object reported by Metzger et al. in the
same reference frame. We measure a magnitude b_J = 23.3 +/- 0.5,
relative to the APM b_J photometric system, which is about 2 mag
brighter than the B = 25.4 reported by Groot et al. for the
extended object on Mar. 9.9 UT. We conclude that the object is the
optical transient reported by Groot et al. on IAUC 6584. Our
observations show that the optical transient, although fading, was
still relatively bright 3.0 days after the gamma-ray burst, and
confirm the close positional coincidence between the optical
transient and the extended object reported by Groot et al. and
Metzger et al. on IAUC 6588."
(C) Copyright 1997 CBAT
1997 April 8 (6618) Daniel W. E. Green
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