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Short GRB 160821B: a reverse shock, a refreshed shock, and a well-sampled kilonova

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Kawaguchi,  K.
Astrophysical and Cosmological Relativity, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;

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Shibata,  M.
Computational Relativistic Astrophysics, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;

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1905.02159.pdf
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Citation

Lamb, G. P., Tanvir, N. R., Levan, A. J., Postigo, A. d. U., Kawaguchi, K., Corsi, A., et al. (2019). Short GRB 160821B: a reverse shock, a refreshed shock, and a well-sampled kilonova. The Astrophysical Journal, 883(1): 48. doi:10.3847/1538-4357/ab38bb.


Cite as: http://hdl.handle.net/21.11116/0000-0004-4504-A
Abstract
We report our identification of the optical afterglow and host galaxy of the short-duration gamma-ray burst sGRB 160821Bb. The spectroscopic redshift of the host is $z=0.162$, making it one of the lowest redshift sGRBs identified by Swift. Our intensive follow-up campaign using a range of ground-based facilities as well as HST, XMM 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, $\theta_j\sim1.9$ 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 magnetised 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 $M_{\rm dyn}=(2.0\pm1.2)\times10^{-3}$\,M$_{\odot}$ and a secular ejecta mass with $M_{\rm pm}= 1.0\pm0.6)\times10^{-2}$\,M$_\odot$, consistent with a binary neutron star merger resulting in a short-lived massive neutron star. This optical and near-infrared dataset provides the best-sampled kilonova light-curve without a gravitational wave trigger to date.