ILLUMINATING THE DARKEST GAMMA-RAY BURSTS WITH RADIO OBSERVATIONS
- Department of Astronomy, Harvard University, Cambridge, MA 02138 (United States)
- Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
- Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany)
- Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91225 (United States)
- Department of Chemistry and Physics, Roger Williams University, Bristol, RI 02809 (United States)
- Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom)
- Max-Planck-Institut fuer Radioastronomie, D-53121 Bonn (Germany)
- Department of Astrophysics, Sackler School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv (Israel)
- National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University Campus, Ganeshkhind, Pune 411007 (India)
- Instituto de Astrofisica de Andalucia (IAA-CSIC), P.O. Box 03004, E-18080 Granada (Spain)
- Institut de Radioastronomie Millimetrique, 300 rue de la Piscine, F-38406 Saint Martin d'Heres (France)
We present X-ray, optical, near-infrared (IR), and radio observations of gamma-ray bursts (GRBs) 110709B and 111215A, as well as optical and near-IR observations of their host galaxies. The combination of X-ray detections and deep optical/near-IR limits establish both bursts as ''dark''. Sub-arcsecond positions enabled by radio detections lead to robust host galaxy associations, with optical detections that indicate z {approx}< 4 (110709B) and z Almost-Equal-To 1.8-2.9 (111215A). We therefore conclude that both bursts are dark due to substantial rest-frame extinction. Using the radio and X-ray data for each burst we find that GRB 110709B requires A{sub V}{sup host}{approx}>5.3 mag and GRB 111215A requires A{sub V}{sup host}{approx}>8.5 mag (assuming z = 2). These are among the largest extinction values inferred for dark bursts to date. The two bursts also exhibit large neutral hydrogen column densities of N{sub H,{sub int}} {approx}> 10{sup 22} cm{sup -2} (z = 2) as inferred from their X-ray spectra, in agreement with the trend for dark GRBs. Moreover, the inferred values are in agreement with the Galactic A{sub V} -N{sub H} relation, unlike the bulk of the GRB population. Finally, we find that for both bursts the afterglow emission is best explained by a collimated outflow with a total beaming-corrected energy of E{sub {gamma}} + E{sub K} Almost-Equal-To (7-9) Multiplication-Sign 10{sup 51} erg (z = 2) expanding into a wind medium with a high density, M Almost-Equal-To (6-20) Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1} (n Almost-Equal-To 100-350 cm{sup -3} at Almost-Equal-To 10{sup 17} cm). While the energy release is typical of long GRBs, the inferred density may be indicative of larger mass-loss rates for GRB progenitors in dusty (and hence metal rich) environments. This study establishes the critical role of radio observations in demonstrating the origin and properties of dark GRBs. Observations with the JVLA and ALMA will provide a sample with sub-arcsecond positions and robust host associations that will help to shed light on obscured star formation and the role of metallicity in GRB progenitors.
- OSTI ID:
- 22126878
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 767; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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