2008/06/02 by J. X. Prochaska, Jason X. Prochaska, Miroslava Dessauges-Zavadsky +5 · 1 citation
Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Afterglow #Astro and Planetary Science #Astronomy #Astrophysics #Galaxy #Gamma-ray burst #Gamma-ray bursts and supernovae #Line-of-sight #Milky Way #Optics #Physics #Spectral line #Star formation #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/590529
Accepted to ApJ, 12 pages, 4 color figures
arxiv created 2008/06/02 · openalex publication_date 2008/09/18 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We survey N V absorption in the afterglow spectra of long-duration gamma-ray bursts (GRBs) with the intent to study highly ionized gas in the galaxies hosting these events. We identify a high incidence (6/7) of spectra exhibiting N V gas with z ≈ z GRB , and the majority show large column densities N (N + 4 ) ≳ 10 14 cm −2 . With one exception, the observed line profiles are kinematically "cold"; i.e., they are narrow and have small velocity offset (δ v≲ 20 km s −1 ) from absorption lines associated with neutral gas. In addition, the N V absorption has similar velocity to that of the UV-pumped fine-structure lines, indicating that these high ions are located within ≈1 kpc of the GRB afterglow. These characteristics are unlike those for N V gas detected in the halo/disk of the Milky Way or along sight lines through high- z damped Lyα systems but resemble the narrow absorption line systems associated with quasars and some high- z starbursts. We demonstrate that GRB afterglows photoionize nitrogen to N +4 at r ≈ 10 pc. This process can produce N V absorption with characteristics resembling the majority of our sample, and we argue that it is the principal mechanism for N +4 along GRB sight lines. Therefore, the observations provide a snapshot of the physical conditions at this distance. In this scenario, the observations imply that the progenitor's stellar wind is confined to r < 10 pc, which suggests that the GRB progenitors occur within dense ( n > 10 3 cm −3 ) environments, typical of molecular clouds. The observations, therefore, primarily constrain the physical conditions—metallicity, density, velocity fields—of the gas within the (former) molecular cloud region surrounding the GRB.