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Illuminating the darkest gamma-ray bursts with radio observations

Zauderer, BA and Berger, E and Margutti, R and Levan, AJ and Olivares E, F and Perley, DA and Fong, W and Horesh, A and Updike, AC and Greiner, J and Tanvir, NR and Laskar, T and Chornock, R and Soderberg, AM and Menten, KM and Nakar, E and Carpenter, J and Chandra, P and Castro-Tirado, AJ and Bremer, M and Gorosabel, J and Guziy, S and Pérez-Ramírez, D and Winters, JM (2013) Illuminating the darkest gamma-ray bursts with radio observations. The Astrophysical Journal, 767 (2). ISSN 1538-4357

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Abstract

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 ≲ 4 (110709B) and z 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 mag and GRB 111215A requires 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 NH, int ≳ 1022 cm-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 AV -N 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 γ + E K (7-9) × 1051 erg (z = 2) expanding into a wind medium with a high density, Myr-1(n 100-350 cm -3 at 1017 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. © 2013. The American Astronomical Society. All rights reserved.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
Date Deposited: 18 May 2017 10:30
Last Modified: 18 May 2017 10:30
DOI or Identification number: 10.1088/0004-637X/767/2/161
URI: http://researchonline.ljmu.ac.uk/id/eprint/6475

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