Central Bureau for Astronomical Telegrams
IAUC 6606: SAX J1750.8-2900 AND GRS 1737-31; GRB 970228
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Circular No. 6606
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SAX J1750.8-2900 AND GRS 1737-31
J. Heise, on behalf of the BeppoSAX Wide Field Camera (WFC)
team (composed of individuals at the Space Research Organization of
the Netherlands, Utrecht; at Istituto di Astrofisica Spaziale, CNR,
Frascati; and at BeppoSAX, Rome) reports on observations made with
the BeppoSAX WFC between Mar. 19.197 and 20.775 UT: "An improved
position of the soft transient x-ray source SAX J1750.8-2900 (IAUC
6597) is R.A. = 17h50m24s, Decl. = -29o01'.9 (equinox 2000.0; error
radius 3'), which is 6'.2 from the variable VLA radio source
reported on IAUC 6601, and 2'.3 from 1RXP J175029-2859.9. Average
intensities were 26 and 22 mCrab at 1.6-7.7 and 7.7-23 keV,
respectively. The hard x-ray transient source GRS 1737-31 (IAUC
6599) was also observed with the WFC, yielding an average intensity
of 11 mCrab over 1.6-7.7 keV and 22 mCrab over 7.7-23 keV. The
source is located at R.A. = 17h40m00s, Decl. = -31o04'.2 (equinox
2000.0; error radius 4'), which is 5'.6 from the reported position
on IAUC 6599."
GRB 970228
K. Sahu, M. Livio, L. Petro, and F. D. Macchetto, Space
Telescope Science Institute, write: "GRB 970228 was observed with
the HST Wide Field and Planetary Camera (WFPC2), between Mar. 26.11
and 26.28 UT, about 26 days after the outburst. The optical
transient (R.A. = 5h01m46s.7, Decl. = +11o46'53".0, equinox 2000.0;
cf. IAUC 6584, 6588) was placed at the center of the Planetary
Camera field-of-view, so as to attain maximum angular resolution.
The other three candidates (two optical and one radio) proposed
earlier as counterparts of GRB 970228 (IAUC 6576, 6574, 6577) are
also within the WFPC2 field-of-view. Observations were taken with
the F606W (wide V) and F814W (I) filters. Four exposures with a
total integration time of 4700 s were taken through the F606W
filter and two exposures with a total integration time of 2400 s
were taken through the F814W filter. The optical counterpart is
clearly detected in both passbands. It was found to be embedded in
an extended source, which can also be seen. The derived magnitudes
for the point source are 25.7 +/- 0.3 and 24.2 +/- 0.3 in the F606W
and F814W filters, respectively. The data were put into the HST
archive on the day of the observations. The data can be accessed
through the Web at http://www.stsci.edu/top.html."
(C) Copyright 1997 CBAT
1997 March 28 (6606) Daniel W. E. Green
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