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IAUC 6660: GRB 970508

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                                                 Circular No. 6660
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 970508
     S. G. Djorgovski, M. R. Metzger, S. R. Kulkarni, S. C. Odewahn,
R. R. Gal, and M. A. Pahre, California Institute of Technology; D.
A. Frail, National Radio Astronomy Observatory; E. Costa and M.
Feroci, and the rest of the BeppoSAX team write:  "Observations at
Palomar indicate that the optical counterpart of GRB 970508 is
continuing to decline in brightness; on May 13.18 UT, its Gunn r-
band magnitude was 20.76 +/- 0.15.  We also detect a faint blue
galaxy with r = 24.8 and g = 24.4, located about 4".3 east and 3".5
north of the variable.  The two may be associated, and/or the
galaxy may be responsible for the absorption lines seen in the
spectrum of the object at z = 0.835 (IAUC 6655)."
     C. Kouveliotou, Universities Space Research Association
(USRA); M. S. Briggs and R. Preece, University of Alabama in
Huntsville (UAH); and G. J. Fishman, C. A. Meegan, and B. A.
Harmon, Marshall Space Flight Center, NASA, report on behalf of the
CGRO BATSE team:  "GRB 970508 is a weak, classical gamma-ray burst
in our data, consisting of a single pulse with duration about 3.6 s
(FWHM) and total duration about 35 s.  The spectrum of the event is
consistent with a single power law with photon index -1.5 +/- 0.05
between 20 and 1000 keV.  Fits with more complex models indicate a
2-sigma lower limit for the energy, where the burst emits most of
its power (E_peak) at about 500 keV.  The estimated total fluence
(20-1000 keV) is (3.1 +/- 0.2) x 10E-6 erg cmE-2, and its peak flux
(50-300 keV) integrated over 1.024 s is (1.66 +/- 0.06) x 10E-7 erg
cmE-2 s.  This peak flux corresponds to an isotropic luminosity of
about 6 x 10E50 erg/s for the reported redshift of 0.835 (IAUC
6655), which agrees with fits to the gamma-ray-burst intensity
distribution.  An earth-occultation search on May 8 and 9 at the
location of the x-ray source (IAUC 6656) reveals no emission up to
a 1-day 3-sigma limit of about 30 mCrab (20-100 keV), assuming the
above power-law spectral shape."
     P. J. Groot and T. J. Galama, University of Amsterdam (UoA);
J. van Paradijs, UoA and UAH; C. Kouveliotou, USRA; M. Centurion
and J. Telting, Isaac Newton Group of Telescopes; P. Smith and C.
Mackey, Kitt Peak National Observatory; and J. Heise and J. in 't
Zand, Space Research Organization of the Netherlands, Utrecht,
report:  "Further optical photometry of the variable reported by
Bond (IAUC 6654) between May 12.00 and 12.06 UT with the 4.2-m
William Herschel Telescope at La Palma shows the following
magnitudes:  U = 20.9 +/- 0.2, B = 20.9 +/- 0.3, V = 20.6 +/- 0.1,
R = 20.2 +/- 0.1, I = 19.7 +/- 0.2.  Corrigenda to IAUC 6655:  on
May 10.0, I = 20.2 +/- 0.2; on May 11.0, I = 19.1 +/- 0.3 and B =
20.3 +/- 0.3."

                      (C) Copyright 1997 CBAT
1997 May 13                    (6660)            Daniel W. E. Green

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