2002/06/29 by N. Mirabal, J. P. Halpern, S. R. Kulkarni +16 · 5 citations
Physics and Astronomy · #Astro and Planetary Science #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/342619
published as Astrophys.J. 578 (2002) 818-832 · 39 pages, 7 figures, accepted for publication in ApJ
arxiv created 2002/06/29 · openalex publication_date 2002/10/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We present sequential optical spectra of the afterglow of GRB 010222 obtained 1 day apart using the Low-Resolution Imaging Spectrometer (LRIS) and the Echellette Spectrograph and Imager (ESI) on the Keck Telescopes. Three low-ionization absorption systems are spectroscopically identified at z 1 = 1.47688, z 2 = 1.15628, and z 3 = 0.92747. The higher resolution ESI spectrum reveals two distinct components in the highest redshift system at z 1 a = 1.47590 and z 1 b = 1.47688. We interpret the z 1 b = 1.47688 system as an absorption feature of the disk of the host galaxy of GRB 010222. The best-fitted power-law optical continuum and [Zn/Cr] ratio imply low dust content or a local gray dust component near the burst site. In addition, we do not detect strong signatures of vibrationally excited states of H 2 . If the gamma-ray burst took place in a superbubble or young stellar cluster, there are no outstanding signatures of an ionized absorber either. Analysis of the spectral time dependence at low resolution shows no significant evidence for absorption-line variability. This lack of variability is confronted with time-dependent photoionization simulations designed to apply the observed flux from GRB 010222 to a variety of assumed atomic gas densities and cloud radii. The absence of time dependence in the absorption lines implies that high-density environments are disfavored. In particular, if the GRB environment was dust free, its density was unlikely to exceed n H I = 10 2 cm -3 . If depletion of metals onto dust is similar to Galactic values or less than solar abundances are present, then n H I ≥ 2 × 10 4 cm -3 is probably ruled out in the immediate vicinity of the burst.