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IAUC 6655: GRB 970508

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                                                 Circular No. 6655
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 970508
     T. J. Galama and P. J. Groot, University of Amsterdam (UoA);
J. van Paradijs, UoA and University of Alabama in Huntsville; C.
Kouveliotou, Universities Space Research Association; M. Centurion,
Isaac Newton Group Telescopes (ING) and Instituto Astrofisico de
Canarias, J. H. Telting, ING; P. Smith and C. Mackey, Kitt Peak
National Observatory (KPNO); and J. Heise and J. in 't Zand, Space
Research Organization of the Netherlands, Utrecht, report
photometry of the variable star reported by Bond (IAUC 6654),
obtained with the 3.5-m WIYN telescope at KPNO on May 9.202 UT and
with the 4.2-m William Herschel Telescope on La Palma during May
10.03-10.07 and 11.01-11.05, confirming that this object is
brightening:  May 9, R = 21.2 +/- 0.1; 10, U = 21.5 +/- 0.2, V =
21.0 +/- 0.1, R = 20.35 +/- 0.1, I = 20.9 +/- 0.2; 11, U = 20.5 +/-
0.2, B = 21.3 +/- 0.2, V = 20.2 +/- 0.1, R = 20.0 +/- 0.1, I = 18.5
(highly uncertain).
     S. G. Djorgovski, M. R. Metzger, S. C. Odewahn, R. R. Gal, S.
R. Kulkarni, and M. A. Pahre, California Institute of Technology
(CIT); D. A. Frail, National Radio Astronomy Observatory; and E.
Costa, M. Feroci, and the rest of the BeppoSAX team, write:  "We
have obtained deep optical images of the field of GRB 970508 at the
Palomar 5-m and 1.5-m telescopes on May 9, 10, and 11 UT.  Bond's
optical variable is measured at R.A. = 6h53m49s.43, Decl. =
+79o16'19".6 (equinox 2000.0), with uncertainties of 1".  Our
preliminary reductions indicate that the source had Gunn r
magnitudes of 21.33, 20.17, and 20.15 on May 9.19, 10.23, and 11.21,
respectively, corresponding to fluxes f(nu) of 11.1, 32.2, and 32.8
microJy at the effective wavelength of 665 nm (estimated total
errors of 10-20 percent).  The Gunn colors measured on May 10.23
were g-r = -0.01 and r-i = +0.02, which can be fitted with a power-
law slope of about -0.5 in f(nu) vs. nu, with large errors.  No
other significantly variable sources brighter than r about 23 have
been detected in the revised GRB error circle."
     Metzger, Djorgovski, C. C. Steidel (CIT), Kulkarni, K. L.
Adelberger (CIT), and Frail further write:  "Spectra of Bond's
variable were obtained using the Keck II 10-m telescope (+ LRIS) on
May 11.25 UT.  The object has no obvious emission lines.  We have
identified a set of aborption features between 430 and 514 nm that
we associate with the Fe II triplet near 237.5 nm, Fe II at 258.6
and 260.2 nm, and Mg II at 279.6 and 280.3 nm, which places this
system at z = 0.835.  Several other absorption features are also
seen.  If the source is associated with GRB 970508, it is evident
that the gamma-ray burst lies at z >/= 0.835.  Absence of prominent
Lyman-alpha forest in the spectrum also suggest that the source is
at redshift z < 2.1."

                      (C) Copyright 1997 CBAT
1997 May 11                    (6655)            Daniel W. E. Green

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