1998/03/30 by F. J. Castander, Francisco J. Castander, D. Q. Lamb +2
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astronomy and Astrophysical Research #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9803324
5 pages, 7 PostScript figures. Uses the AIP conference proceedings LaTeX macros. To appear in the proceedings of the Fourth Huntsville Gamma-Ray Burst Symposium
arxiv created 1998/03/30 · arxiv updated 2009/12/01
The IRAS 100 micron image of the GRB 970228 field shows that the amount of galactic dust in this direction is substantial and varies on arcminute angular scales. From an analysis of the observed surface density of galaxies in the 2.6' × 2.6' HST WFPC image of the GRB 970228 field, we find AV = 1.1 ± 0.10. From an analysis of the observed spectra of three stars in the GRB 970228 field, we find AV = 1.71+0.20-0.40. This value may represent the best estimate of the extinction in the direction of GRB 970228, since these three stars lie only 2.7'', 16'', and 42'' away from the optical transient. If instead we combine the two results, we obtain a conservative value AV = 1.3 ± 0.2. This value is significantly larger than the values AV = 0.4 - 0.8 used in papers to date. The value of AV that we find implies that, if the extended source in the burst error circle is extragalactic and therefore lies beyond the dust in our own galaxy, its optical spectrum is very blue: its observed color (V-Ic)obs ≈ 0.65+0.74-0.94 is consistent only with a starburst galaxy, an irregular galaxy at z > 1.5, or a spiral galaxy at z > 2. On the other hand, its observed color and surface brightness μV ≈ 24.5 arcsec-2 are similar to those expected for the reflected light from a dust cloud in our own galaxy, if the cloud lies in front of most of the dust in this direction.