Central Bureau for Astronomical Telegrams
IAUC 6732: GRB 970828; GRB 970228
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Circular No. 6732
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 970828
T. Murakami and Y. Ueda, Institute of Space and Astronautical
Science; A. Yoshida and N. Kawai, Institute of Physical and
Chemical Research; and F. E. Marshall, R. H. D. Corbet, and T.
Takeshima, Goddard Space Flight Center, report on behalf of the
ASCA and RXTE teams: "We analyzed all of the ASCA observational
data from Aug. 29.91 to 30.85 UT (net exposure 36 000 s). After
the attitude determination, we refined the ASCA x-ray position
(reported on IAUC 6729) to R.A. = 18h08m32s.2, Decl. = +59o18'54"
(equinox 2000.0; error radius 0'.5). Its average flux in the band
2-10 keV is 4 x 10E-13 erg cmE-2 sE-1. The fluxes clearly show
fading behavior. This strongly supports the conclusion that the
ASCA x-ray source is a fading x-ray source associated with GRB
970828 (IAUC 6726, 6728). Considering the flux reported by the
PCA/RXTE observations (IAUC 6727), together with the ASCA fluxes,
the x-ray source appears to be fading consistent with a time power-
law having an index of about -1.4."
GRB 970228
S. R. Kulkarni, S. G. Djorgovski, and J. C. Clemens,
California Institute of Technology, report: "On Aug. 13 UT, we
used the Low Resolution Imaging Spectrograph mounted on the Keck II
telescope to acquire spectra at the position of the GRB 970228
optical transient reported on IAUC 6584. We placed a 1".5 slit
(p.a. 87 deg) at the location specified on IAUC 6588 (Metzger et
al.), and used a low-resolution grating (300 lines/mm blazed at 500
nm) to acquire exposures totalling 1800 s. A spectral trail is
well detected in this location. The spectrum has some weak
features but no strong emission lines. Extraction of a reliable
magnitude of the object from the spectrum is difficult; the
detected flux is consistent with an object of magnitude R about
24-25."
S. G. Djorgovski, S. R. Kulkarni, R. R. Gal, and S. C. Odewahn,
California Institute of Technology; and D. A. Frail, National Radio
Astronomy Observatory, report: "We obtained deep CCD images of the
field of GRB 970228 with the Palomar 5-m Hale telescope, in
subarcsecond seeing, on Sept. 4 UT. We confirm the existence of a
faint object (magnitude R about 25.5) associated with the optical
transient (IAUC 6588, 6606) and recently detected spectroscopically
with the Keck II 10-m telescope by Kulkarni et al. (see above).
The brightness of the source is fully consistent with the previous
measurements of the nebulosity adjacent to the optical transient.
We interpret this to be the host galaxy of GRB 970228."
(C) Copyright 1997 CBAT
1997 September 4 (6732) Daniel W. E. Green
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