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IAUC 6656: GRB 970508

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                                                 Circular No. 6656
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
     L. Piro, E. Costa, M. Feroci, and P. Soffitta, Istituto di
Astrofisica Spaziale, CNR, Frascati; L. A. Antonelli, F. Fiore, and
P. Giommi, BeppoSAX, Rome; A. Owens and A. Parmar, Space Science
Department, ESTEC; S. Molendi, Istituto di Fisica Cosmica e
Tecnologie Relative, CNR, Milano; G. Cusumano, Istituto di Fisica
Cosmica e Applicazioni Informatica, CNR, Palermo; J. in 't Zand and
J. Heise, Space Research Organization of the Netherlands, Utrecht;
F. Frontera and G. Zavattini, Universita di Ferrara; L. Nicastro
and E. Palazzi, Istituto Tecnologie e Studio Radiazioni
Extraterrestri, CNR, Bologna; M. Smith, G. Gandolfi, V. Torroni, G.
Spoliti, A. Coletta, M. Capalbi, S. Rebecchi, D. Ricci, L. Bruca,
and G. Crisigiovanni, BeppoSAX, Rome; L. Salotti, G. Gennaro, and
C. DeLibero, Nuova Telespazio, Rome; and R. C. Butler, Agenzia
Spaziale Italiana, Rome, report:  "The BeppoSAX GRBM/WFC error box
of GRB 970508 was observed with the BeppoSAX Narrow Field
Instruments (NFI) on May 9.1375 UT for about 36 000 s (about 5.7 hr
after the gamma-ray burst).  A previously unknown x-ray source,
1SAX J0653.8+7916, has been detected by the MECS (units 2 and 3)
and LECS at R.A. = 6h53m46s.7, Decl. = +79o16'02" (equinox 2000.0;
estimated error radius 50").  This position lies in the BeppoSAX
WFC error box (IAUC 6649, 6654).  The previously known source, 1RXS
J065213.8+790855, lying outside the WFC error box, is also detected
at R.A. = 6h52m14s.8, Decl. = +79o09'16", consistent within the
errors with the ROSAT measurement.  The countrates of 1SAX
J0653.8+7916 were 0.0070 +/- 0.0007 and 0.0043 +/- 0.0006 count/s
in the MECs (2-10 keV) and LECS (0.5-5 keV), respectively,
corresponding to fluxes of (6.3 +/- 0.6) and (7.0 +/- 0.8) x 10E-13
erg cmE-2 sE-1.  The optical transient reported on IAUC 6654
coincides, within the errors, with 1SAX J0653.8+7916.  A further
observation with the BeppoSAX NFI is foreseen on May 11 to study
the temporal evolution."
     A. O. Jaunsen, and T. Grav, Institute for Theoretical
Astrophysics, Oslo; R. Oestensen, Nordic Optical Telescope (NOT);
H. Pedersen, Copenhagen University Observatory; and Piro, Feroci,
Costa, Frontera, Palazzi, and Heise report:  "Data taken at the
2.56-m NOT confirms the variability of the source reported by Bond
(IAUC 6654).  On May 10.92 UT, we found V = 19.65 for the candidate,
V = 20.10 for the nearby star; these magnitudes were calibrated
against GSC 4534.1515 (V = 13.3).  Unfiltered images taken during
the two preceding nights further document the rise in brightness."

                      (C) Copyright 1997 CBAT
1997 May 11                    (6656)            Daniel W. E. Green

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