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A Jet Break in the X-ray Light Curve of Short GRB 111020A: Implications for Energetics and RatesWe present broadband observations of the afterglow and environment of the short GRB 111020A. An extensive X-ray light curve from Swift/XRT, XMM-Newton, and Chandra, spanning approx.100 s to 10 days after the burst, reveals a significant break at (delta)t approx. = 2 days with pre- and post-break decline rates of (alpha)X,1 approx. = -0.78 and (alpha)X,2 < or approx. 1.7, respectively. Interpreted as a jet break, we infer a collimated outflow with an opening angle of (theta)j approx. = 3deg - 8deg. The resulting beaming-corrected gamma-ray (10-1000 keV band) and blast-wave kinetic energies are (2-3) x 10(exp 48) erg and (0.3-2) x 10(exp 49) erg, respectively, with the range depending on the unknown redshift of the burst. We report a radio afterglow limit of <39 micro-Jy (3(sigma)) from Expanded Very Large Array observations that, along with our finding that v(sub c) < v(sub X), constrains the circumburst density to n(sub 0) approx.0.01 0.1/cu cm. Optical observations provide an afterglow limit of i > or approx.24.4 mag at 18 hr after the burst and reveal a potential host galaxy with i approx. = 24.3 mag. The subarcsecond localization from Chandra provides a precise offset of 0".80+/-0".11 (1(sigma))from this galaxy corresponding to an offset of 5.7 kpc for z = 0.5-1.5. We find a high excess neutral hydrogen column density of (7.5+/-2.0) x 10(exp 21)/sq cm (z = 0). Our observations demonstrate that a growing fraction of short gamma-ray bursts (GRBs) are collimated, which may lead to a true event rate of > or approx.100-1000 Gpc(sup -3)/yr, in good agreement with the NS-NS merger rate of approx. = 200-3000 Gpc(sup -3)/ yr. This consistency is promising for coincident short GRB-gravitational wave searches in the forthcoming era of Advanced LIGO/VIRGO.
Document ID
20130012535
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1088/0004-637X/756/2/189
Authors
Fong, W. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Berger, E. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Margutti, R. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Zauderer, B. A. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Troja, E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Czekala, I. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Chornock, R. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Gehrels, N. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Sakamoto, T. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Fox, D. B. (Pennsylvania State Univ. University Park, PA, United States)
Podsiadlowski, P. (Oxford Univ. Oxford, United Kingdom)
Date Acquired
August 27, 2013
Publication Date
August 27, 2012
Publication Information
Publication: The Astrophysical Journal
Volume: 756
Issue: 2
Subject Category
Astronomy
Report/Patent Number
GSFC-E-DAA-TN6804
Funding Number(s)
CONTRACT_GRANT: NNG06EO90A
CONTRACT_GRANT: GO1-12072X
CONTRACT_GRANT: NNX10AI24G
CONTRACT_GRANT: NSF AST-1107973
CONTRACT_GRANT: NAS8-03060
Distribution Limits
Public
Copyright
Public Use Permitted.

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