TY - JOUR
T1 - A jet break in the x-ray light curve of short GRB111020A
T2 - Implications for energetics and rates
AU - Fong, W.
AU - Berger, E.
AU - Margutti, R.
AU - Zauderer, B. A.
AU - Troja, E.
AU - Czekala, I.
AU - Chornock, R.
AU - Gehrels, N.
AU - Sakamoto, T.
AU - Fox, D. B.
AU - Podsiadlowski, P.
PY - 2012/9/10
Y1 - 2012/9/10
N2 - We present broadband observations of the afterglow and environment of the short GRB111020A. An extensive X-ray light curve from Swift/XRT, XMM-Newton, and Chandra, spanning ∼100 s to 10days after the burst, reveals a significant break at δt ≈ 2days with pre- and post-break decline rates of αX,1 ≈ -0.78 and αX,2 ≲ -1.7, respectively. Interpreted as a jet break, we infer a collimated outflow with an opening angle of θj ≈ 3°-8°. The resulting beaming-corrected γ-ray (10-1000keV band) and blast-wave kinetic energies are (2-3) × 1048erg and (0.3-2) × 1049erg, respectively, with the range depending on the unknown redshift of the burst. We report a radio afterglow limit of <39 μJy (3σ) from Expanded Very Large Array observations that, along with our finding that νc < νX, constrains the circumburst density to n 0 0.01-0.1cm-3. Optical observations provide an afterglow limit of i ≳ 24.4mag at 18hr after the burst and reveal a potential host galaxy with i 24.3mag. The subarcsecond localization from Chandra provides a precise offset of 080 ± 011 (1σ) from this galaxy corresponding to an offset of 5-7kpc for z = 0.5-1.5. We find a high excess neutral hydrogen column density of (7.5 ± 2.0) × 1021cm-2 (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 ≳ 100-1000Gpc-3yr-1, in good agreement with the NS-NS merger rate of ≈200-3000Gpc-3yr-1. This consistency is promising for coincident short GRB-gravitational wave searches in the forthcoming era of Advanced LIGO/VIRGO.
AB - We present broadband observations of the afterglow and environment of the short GRB111020A. An extensive X-ray light curve from Swift/XRT, XMM-Newton, and Chandra, spanning ∼100 s to 10days after the burst, reveals a significant break at δt ≈ 2days with pre- and post-break decline rates of αX,1 ≈ -0.78 and αX,2 ≲ -1.7, respectively. Interpreted as a jet break, we infer a collimated outflow with an opening angle of θj ≈ 3°-8°. The resulting beaming-corrected γ-ray (10-1000keV band) and blast-wave kinetic energies are (2-3) × 1048erg and (0.3-2) × 1049erg, respectively, with the range depending on the unknown redshift of the burst. We report a radio afterglow limit of <39 μJy (3σ) from Expanded Very Large Array observations that, along with our finding that νc < νX, constrains the circumburst density to n 0 0.01-0.1cm-3. Optical observations provide an afterglow limit of i ≳ 24.4mag at 18hr after the burst and reveal a potential host galaxy with i 24.3mag. The subarcsecond localization from Chandra provides a precise offset of 080 ± 011 (1σ) from this galaxy corresponding to an offset of 5-7kpc for z = 0.5-1.5. We find a high excess neutral hydrogen column density of (7.5 ± 2.0) × 1021cm-2 (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 ≳ 100-1000Gpc-3yr-1, in good agreement with the NS-NS merger rate of ≈200-3000Gpc-3yr-1. This consistency is promising for coincident short GRB-gravitational wave searches in the forthcoming era of Advanced LIGO/VIRGO.
KW - gamma-ray burst: general
KW - gamma-ray burst: individual (111020A)
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U2 - 10.1088/0004-637X/756/2/189
DO - 10.1088/0004-637X/756/2/189
M3 - Article
AN - SCOPUS:84865610493
SN - 0004-637X
VL - 756
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 189
ER -