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Astron. Astrophys. 326, L13-L16

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Letter to the Editor

HST Data suggest proper motion
for the optical counterpart of GRB 970228*

P.A. Caraveo1, R.P. Mignani2, M. Tavani1,3, and G.F. Bignami4,1

1 Istituto di Fisica Cosmica del CNR, Milano, Italy
2 Max-Plack-Institute für Extraterrestrische Physik, Garching, Germany
3 Columbia University, New York, USA
4 Agenzia Spaziale Italiana, Roma, Italy

Received 23 May 1997 / Accepted 19 June 1997


After a quarter of a century of FORMULA -ray burst (GRB) astronomy, the Italian-Dutch satellite BeppoSAX on Feb 28th, 1997 detected a soft X-ray afterglow from GRB 970228 and positioned it accurately. This made possible the successful detection of an optical transient.
Two public Hubble Space Telescope (HST) images of the GRB/optical transient region were taken on March 26th and April 7th, 1997. They are analyzed here, with the purpose of understanding the nature of GRB 970228. We find that the position of the faint point-like object ( FORMULA ) seen at the transient location changed by FORMULA pixels in 12 days, corresponding to a proper motion of ~ 550 mas/year. By comparison, four adjacent sources in the same field do not show any significant displacement, with astrometric residuals close to zero and average absolute displacements less than 0.09 pixels. If confirmed, this result would strongly support the galactic nature of GRB 970228.

Key words: Gamma Ray Burst, optical, GRB970228

*Based on observations with the NASA/ESA Hubble Space Telescope

Send offprint requests to: P. Caraveo, pat@ifctr.mi.cnr.it

© European Southern Observatory (ESO) 1997

Online publication: October 1, 1997
Last change: April 8, 1998