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The Afterglow, Energetics, and Host Galaxy of the Short-Hard Gamma-Ray Burst 051221a

Soderberg, A. M. and Berger, E. and Kasliwal, M. M. and Frail, D. A. and Price, P. A. and Schmidt, B. P. and Kulkarni, S. R. and Fox, D. B. and Cenko, S. B. and Gal-Yam, A. and Nakar, E. and Roth, K. C. (2006) The Afterglow, Energetics, and Host Galaxy of the Short-Hard Gamma-Ray Burst 051221a. Astrophysical Journal, 650 (1). pp. 261-271. ISSN 0004-637X.

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We present detailed optical, X-ray, and radio observations of the bright afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift XRT, and the Very Large Array, as well as optical spectra from which we measure the redshift of the burst, z = 0.5464. At this redshift the isotropic-equivalent prompt energy release was about 1.5 × 10^(51) ergs, and using a standard afterglow synchrotron model, we find that the blast wave kinetic energy is similar, E_(K,iso) ≈ 8.4 × 10^(51) ergs. An observed jet break at t approx 5 days indicates that the opening angle is θ_j ≈ 7° and the total beaming-corrected energy is therefore ≈ 2.5 × 10^(49) ergs, comparable to the values inferred for previous short GRBs. We further show that the burst experienced an episode of energy injection by a factor of 3.4 between t = 1.4 and 3.4 hr, which was accompanied by reverse shock emission in the radio band. This result provides continued evidence that the central engines of short GRBs may be active significantly longer than the duration of the burst and/or produce a wide range of Lorentz factors. Finally, we show that the host galaxy is actively forming stars at a rate of about 1.6 M_☉ yr^(-1), yet exhibits evidence for an appreciable population of old stars (~1 Gyr) and near-solar metallicity. These properties are intermediate between those of long GRB hosts and previous short burst hosts. The lack of bright supernova emission and the low circumburst density (n ~ 10^(-3) cm^(-3)), however, continue to support the idea that short bursts are not related to massive stellar death. Given that the total energy release is larger than the predicted yield for a neutrino annihilation mechanism, this suggests that magnetohydrodynamic processes may be required to power the burst.

Item Type:Article
Related URLs:
URLURL TypeDescription
Berger, E.0000-0002-9392-9681
Kasliwal, M. M.0000-0002-5619-4938
Schmidt, B. P.0000-0001-6589-1287
Kulkarni, S. R.0000-0001-5390-8563
Fox, D. B.0000-0002-3714-672X
Cenko, S. B.0000-0003-1673-970X
Gal-Yam, A.0000-0002-3653-5598
Nakar, E.0000-0002-4534-7089
Additional Information:© 2006 American Astronomical Society. Received 2006 January 20; accepted 2006 June 2. The authors thank S. Rosswog for helpful discussions. As always, the authors thank Jochen Greiner for maintaining his GRB page. A. M. S. and S. B. C. are supported by the NASA Graduate Student Research Program. E. B. is supported by NASA through Hubble Fellowship grant HST-HF-01171.01 awarded by the STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. A. G. acknowledges support by NASA through Hubble Fellowship grant HST-HF-01158.01-A awarded by STScI. K. R. is supported by the Gemini Observatory, which provided observations presented in this paper, and which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil ), and CONICET (Argentina). GRB research at Caltech is supported through NASA.
Funding AgencyGrant Number
NASA Graduate Student Research FellowshipUNSPECIFIED
NASA Hubble FellowshipHST-HF-01171.01
NASA Hubble FellowshipHST-HF-01158.01-A
Gemini ObservatoryUNSPECIFIED
Subject Keywords:gamma rays: bursts
Issue or Number:1
Record Number:CaltechAUTHORS:20110616-112241756
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Official Citation:The Afterglow, Energetics, and Host Galaxy of the Short-Hard Gamma-Ray Burst 051221a A. M. Soderberg et al. 2006 ApJ 650 261
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24031
Deposited By: Jason Perez
Deposited On:16 Jun 2011 20:09
Last Modified:20 Nov 2019 22:46

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