2003/01/14 by Lifan Wang, Wang, Lifan, D. Baade +6
Engineering · Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #Gamma-ray bursts and supernovae #SAS software applications and methods #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0301266
Submitted to ApJL
arxiv created 2003/01/14 · openalex publication_date 2003/01/14 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We present spectropolarimetry observations of GRB 021004 obtained at the ESO VLT. We detect a remarkable increase of the degree of polarization blueward of the host galaxy rest frame Ly-alpha to about 5-10% that corresponds to a decrease in the continuum flux below the extrapolation of a power law. An increase of the degree of polarization is perhaps also recorded in some narrow lines, but of lower statistical significance. The broad polarization feature blueward of the Ly-alpha absorption line at 4040 Åis at least partially produced by hydrogen-rich material with velocities approaching 40,000 \kms located beyond the front of the afterglow shock, rather than due entirely to intergalactic Ly-alpha absorption systems on the line of sight to the GRB. The presence of the broad Ly-alpha absorption provides evidence that the GRB occurred inside the ejecta from a hydrogen-rich supernova that exploded before the GRB.