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

G. P. Lamb, N. R. Tanvir, A. J. Levan, A. De Ugarte Postigo, K. Kawaguchi, A. Corsi, P. A. Evans, B. Gompertz, D. B. Malesani, K. L. Page, K. Wiersema, S. Rosswog, M. Shibata, M. Tanaka, A. J.Van Der Horst, Z. Cano, J. P.U. Fynbo, A. S. Fruchter, J. Greiner, K. E. HeintzA. Higgins, J. Hjorth, L. Izzo, P. Jakobsson, D. A. Kann, P. T. O'Brien, D. A. Perley, E. Pian, G. Pugliese, R. L.C. Starling, C. C. Thöne, D. Watson, R. A.M.J. Wijers, D. Xu

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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, 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 o and a secular (post-merger) ejecta mass with M pm = (1.0 ±0.6) ×10-2 M o, 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.

Original languageEnglish
Article number48
JournalAstrophysical Journal
Volume883
Issue number1
DOIs
StatePublished - Sep 20 2019

Keywords

  • gamma-ray burst: individual (GRB 160821B)
  • stars: neutron

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    Lamb, G. P., Tanvir, N. R., Levan, A. J., Postigo, A. D. U., Kawaguchi, K., Corsi, A., Evans, P. A., Gompertz, B., Malesani, D. B., Page, K. L., Wiersema, K., Rosswog, S., Shibata, M., Tanaka, M., Horst, A. J. V. D., Cano, Z., Fynbo, J. P. U., Fruchter, A. S., Greiner, J., ... Xu, D. (2019). Short GRB 160821B: A Reverse Shock, a Refreshed Shock, and a Well-sampled Kilonova. Astrophysical Journal, 883(1), [48]. https://doi.org/10.3847/1538-4357/ab38bb