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IAUC 6635: GRB 970228; C/1995 O1

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                                                 Circular No. 6635
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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URL http://cfa-www.harvard.edu/cfa/ps/cbat.html
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GRB 970228
     F. Pedichini, A. Di Paola, and L. Stella, Osservatorio
Astronomico di Roma; G. Gandolfi, G. Spoliti, L. Di Ciolo, A.
Coletta, G. D'Andreta, J. M. Muller, and M. Capalbi, BeppoSAX, Rome;
A. Boattini, E. Costa, M. Feroci, and L. Piro, Istituto Astrofisica
Spaziale, CNR, Frascati; E. Palazzi, D. Dal Fiume and L. Nicastro,
Istituto Tecnologie e Studio Radiazioni Extraterrestri (TESRE), CNR,
Bologna; F. Frontera, Universita di Ferrara and TESRE; and R. Jager,
J. Heise, and J. in 't Zand, Space Research Organization of the
Netherlands, Utrecht, communicate:  "Broadband (peak 700 nm, FWHM
300 nm) CCD images of the field of GRB 970228 (IAUC 6572, 6576)
sampled at 1".67/pixel were obtained with the Rome Astronomical
Observatory's 0.90-m Schmidt telescope at Campo Imperatore on Feb.
28.81 and Mar. 4.81 UT (exposure 1500 s).  During the first
observation, we detected an object at a position consistent (within
our 0".7 uncertainty) with the optical transient reported on IAUC
6584.  The flux from this object had decreased by more than 2.7 mag
on Mar. 4.81, when we obtained only an upper limit.  On Feb. 28.81,
the optical transient was 1.6 +/- 0.5 mag brighter in our band than
the faint nearby K dwarf star (IAUC 6588, 6620).  Our results
confirm the presence of a large variation in the likely optical
counterpart of GRB 970228 and testify that the optical transient
had started at least 5 hr before the first observation reported on
IAUC 6584 (see also Guarnieri et al., Nature, submitted)."

     M. Kidger, Instituto de Astrofisica de Canarias (IAC), reports
on behalf of the European Hale-Bopp Team that near-infrared
observing runs of up to 11 hr were undertaken for comet C/1995 O1
with narrow-band Br-gamma, CO, and K-continuum filters at the 1.5-m
Carlos Sanchez Telescope (+ CAIN infrared camara with NICMOS array)
on a number of days around perihelion.  Analysis of the data taken
by B. Goetz (University of Munich) and J. Licandro (IAC) supports
the period of rotation of the nucleus suggested by Lecacheux et al.
(IAUC 6560) and since refined by Jorda et al. (IAUC 6583) and by
Sarmecancic et al. (IAUC 6600), giving a value of 11.20 +/- 0.04 hr
for 1997 Mar. 31-Apr. 2.  These data, together with previously
published results, suggest that the period of the reported
modulation of the rotation period may be as short as 18 days.
Further long runs of data are being analyzed, and observations are
continuing in an attempt to define this modulation more exactly.

                      (C) Copyright 1997 CBAT
1997 April 22                  (6635)            Daniel W. E. Green

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