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IAUC 6570: GRB 960720

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                                                 Circular No. 6570
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 960720
    J. Greiner, Astrophysical Institute, Potsdam; and J. Heise,
Space Research Organization of the Netherlands, communicate:  "The
brightest of the nine x-ray sources detected with the ROSAT HRI on
1996 Aug. 31 (IAUC 6487), RX J1730.7+4906, is located within the
revised error circle of GRB 960720 (IAUC 6569).  It coincides with
QSO 1729+491 (= 4C 49.29), which is a strong radio source at z =
1.038 (Walsh et al. 1984, MNRAS 211, 105).  Its HRI countrate of
0.0041 +/- 0.0009 count/s corresponds to an unabsorbed x-ray
luminosity of 5 x 10E44 erg/s in the range 0.1-2.4 keV (assuming a
power-law spectrum of photon index 1.9, corrected for galactic
absorption).  The likelihood for the positional coincidence of a
radio-loud AGN of that x-ray and radio brightness with the 3' GRB
error box is about 2 x 10E-4 (Brinkmann et al. 1995, A.Ap. Suppl.
109, 147)."
     L. Piro, E. Costa, M. Feroci, and M. Cinti, Istituto di
Astrofisica Spaziale, Consiglio Nazionale delle Ricerche (CNR),
Frascati; F. Frontera, D. Dal Fiume, L. Nicastro, M. Orlandini, and
G. Pizzichini, Istituto Tecnologie e Studio Radiazioni
Extraterrestri, CNR, Bologna; J. Heise and R. Jager, Space Research
Organization of the Netherlands, Utrecht; F. Fiore, P. Giommi, A.
Antonelli, and J. M. Muller, BeppoSAX Science Data Center, Rome; A.
Parmar, Space Science Department, ESTEC, The Netherlands; M. C.
Maccarone, Istituto Fisica Cosmica e Applicazioni Informatica, CNR,
Palermo; L. Chiappetti, Istituto di Fisica Cosmica e Tecnologie
Relative, CNR, Milan; and R. C. Butler, Agenzia Spaziale Italiana,
Rome, report:  "We analyzed data from the BeppoSAX follow-up
observation of the Wide-Field-Camera field of GRB 960720 (IAUC 6467,
6480) made on Sept. 3.715-4.708 UT.  Within the updated error
region of this GRB (IAUC 6569), we detect one source with a
probability of chance occurrence of about 1 x 10E-4.  The estimated
x-ray flux (2-10 keV) is (1.0 +/- 0.3) x 10E-13 erg cmE-2 sE-1, and
the source is located at R.A. = 17h30m45s, Decl. = +49o06'.1
(equinox J2000.0; conservative error radius of 50"); this position
is coincident with that of a bright radio-loud QSO, 4C 49.29, which
we identify as the counterpart of the x-ray source.  The
probability that such a (radio) bright QSO is found by chance
within the WFC error box is < 2 x 10E-4.  However, we note that
this is the only case so far reported of an object of this type
being associated to a small (a few arcmin**2) GRB error box."

                      (C) Copyright 1997 CBAT
1997 March 1                   (6570)            Daniel W. E. Green

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