1997A&A...326L..13C

After a quarter of a century of γ-ray burst (GRB) astronomy, the Italian-Dutch satellite BeppoSAX on Feb 28^th, 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 26^th and April 7^th, 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 (m_v∼26) seen at the transient location changed by 0.40±0.10pixels in 12 days, corresponding to a proper motion of ∼550mas/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 0.09pixels. If confirmed, this result would strongly support the galactic nature of GRB 970228.