Short GRB 160821B: A Reverse Shock, a Refreshed Shock, and a Well-sampled Kilonova

Journal
Date Issued
2019
Author(s)
Lamb, G. P.
•
Tanvir, N. R.
•
Levan, A. J.
•
de Ugarte Postigo, A.
•
Kawaguchi, K.
•
Corsi, A.
•
Evans, P. A.
•
Gompertz, B.
•
Malesani, D. B.
•
Page, K. L.
•
Wiersema, K.
•
Rosswog, S.
•
Shibata, M.
•
Tanaka, M.
•
van der Horst, A. J.
•
Cano, Z.
•
Fynbo, J. P. U.
•
Fruchter, A. S.
•
Greiner, J.
•
Heintz, K. E.
•
Higgins, A.
•
Hjorth, J.
•
Izzo, L.
•
Jakobsson, P.
•
Kann, D. A.
•
O'Brien, P. T.
•
Perley, D. A.
•
•
Pugliese, G.
•
Starling, R. L. C.
•
Thöne, C. C.
•
Watson, D.
•
Wijers, R. A. M. J.
•
Xu, D.
DOI
Abstract
We report our identification of the optical afterglow and host galaxy of the short-duration gamma-ray burst sGRB 160821B. The spectroscopic redshift of the host is z = 0.162, making it one of the lowest redshift short-duration gamma-ray bursts (sGRBs) identified by Swift. Our intensive follow-up campaign using a range of ground-based facilities as well as Hubble Space Telescope, XMM-Newton, and Swift, shows evidence for a late-time excess of optical and near-infrared emission in addition to a complex afterglow. The afterglow light curve at X-ray frequencies reveals a narrow jet, {θ }j∼ {1.9}-0.03+0.10 deg, that is refreshed at >1 day post-burst by a slower outflow with significantly more energy than the initial outflow that produced the main GRB. Observations of the 5 GHz radio afterglow shows a reverse shock into a mildly magnetized shell. The optical and near-infrared excess is fainter than AT2017gfo associated with GW170817, and is well explained by a kilonova with dynamic ejecta mass M dyn = (1.0 ± 0.6) × 10-3 M ☉ and a secular (post-merger) ejecta mass with M pm = (1.0 ± 0.6) × 10-2 M ☉, consistent with a binary neutron star merger resulting in a short-lived massive neutron star. This optical and near-infrared data set provides the best-sampled kilonova light curve without a gravitational wave trigger to date.
Volume
883
Issue
1
Start page
48
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2019ApJ...883...48L
Rights
open.access
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