1998/07/30 by J. S. Bloom, S. G. Djorgovski, S. R. Kulkarni +1 · 9 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/311682
published as Astrophys.J. 507 (1998) L25-L28 · Submitted to the Astrophysical Journal Letters (30 July 1998). Five pages including one table and two figures, written in LaTeX using the emulateapj and psfig macros
arxiv created 1998/07/30 · openalex publication_date 1998/11/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We present late-time imaging and spectroscopic observations of the optical transient (OT) and host galaxy of GRB 970508. Imaging observations roughly 200 and 300 days after the burst provide unambiguous evidence for the flattening of the light curve. The spectroscopic observations reveal two persistent features that we identify with [O II] λ3727 and [Ne III] λ3869 at a redshift of z =0.835—the same redshift as the absorption system seen when the transient was bright. The OT was coincident with the underlying galaxy to better than 370 mas or a projected radial separation of less than 2.7 kpc. The luminosity of the [O II] line implies a minimum star formation rate of 1 M ☉ yr -1 . In our assumed cosmology, the implied rest-frame absolute magnitude is M B =-18.55, or L B =0.12 L * . This object, the likely host of GRB 970508, can thus be characterized as an actively star-forming dwarf galaxy. The close spatial connection between this dwarf galaxy and the OT requires that at least some fraction of gamma-ray burst progenitors are not ejected in even the weakest galactic potentials.