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Title: Can an off-axis gamma-ray burst jet in GW170817 explain all the electromagnetic counterparts?
Authors: Ioka, Kunihito  kyouindb  KAKEN_id  orcid (unconfirmed)
Nakamura, Takashi
Author's alias: 井岡, 邦仁
中村, 卓史
Issue Date: Apr-2018
Publisher: Physical Society of Japan
Journal title: Progress of Theoretical and Experimental Physics
Volume: 2018
Issue: 4
Thesis number: 043E02
Abstract: Gravitational waves from a merger of two neutron stars (NSs) were discovered for the first time in GW170817, together with diverse electromagnetic (EM) counterparts. To make constraints on a relativistic jet from the NS merger, we calculate the EM signals in (1) the short gamma-ray burst sGRB 170817A from an off-axis jet, (2) the optical–infrared macronova (or kilonova), especially the blue macronova, from a jet-powered cocoon, and (3) the X-ray and radio afterglows from the interaction between the jet and interstellar medium. We find that a typical sGRB jet is consistent with these observations, and there is a parameter space to explain all the observations in a unified fashion with an isotropic energy ~ 10⁵¹ - 10⁵² erg, opening angle ~ 20°, and viewing angle ~ 30°. The off-axis emission is less de-beamed than the point-source case because the viewing angle is comparable to the opening angle. We also analytically show that the jet energy accelerates a fair fraction of the merger ejecta to a sub-relativistic velocity ~0.3 - 0.4c as a cocoon in a wide parameter range. The ambient density might be low ~ 10⁻³ - 10⁻⁶ cm⁻³, which can be tested by future observations of radio flares and X-ray remnants.
Rights: © The Author(s) 2018. Published by Oxford University Press on behalf of the Physical Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
DOI(Published Version): 10.1093/ptep/pty036
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