2000/07/21 by A. O. Jaunsen, J. Hjorth, G. Bjornsson +8 · 6 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/318266
published as Astrophys.J. 546 (2001) 127-133 · 11 pages, including 2 tables and 3 figures. Accepted for publication in ApJ, part 1
arxiv created 2000/07/21 · openalex publication_date 2001/01/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
We present extensive multicolor ( UBVR C I C ) photometry of the optical afterglow of GRB 980519. Upon discovery, 8.3 hr after the burst, the source was decaying as a power law, ( t - t GRB ) α , with a rapid decay rate α 1 = -1.73 ± 0.04. About 13 hr after the burst a steepening of the light curve to α 2 = -2.22 ± 0.04 was observed. Within the framework of current afterglow models, we argue that the rapid initial decline, the "break" in the light curve, and the spectral properties of the afterglow are best interpreted as being due to a collimated ultrarelativistic jet of fixed opening angle expanding into an inhomogeneous medium. In this scenario, we find that the circumburst medium has a density structure that goes as r -2.05±0.22 . This is characteristic of a preexisting wind expelled from a massive star. A possible physical scenario is that the progenitor star collapsed to form a black hole (i.e., a "collapsar"), producing the observed burst and afterglow. However, the supernova signature expected in the light curve in such a scenario is not detected. This either implies that the redshift of GRB 980519 is greater than 1.5 or that supernovae accompanying GRBs are not standard candles.