2019MNRAS.485.2155L -
Mon. Not. R. Astron. Soc., 485, 2155-2166 (2019/May-2)
Non-thermal afterglow of the binary neutron star merger GW170817: a more natural modelling of electron energy distribution leads to a qualitatively different new solution.
LIN H., TOTANI T. and KIUCHI K.
Abstract (from CDS):
The observed non-thermal afterglow spectra of the binary neutron star (BNS) merger GW170817 from radio to X-ray are consistent with synchrotron radiations by shock-accelerated electrons. However, previous afterglow modelling studies were based on a simplified assumption that the acceleration efficiency is extremely high; that is, all electrons in the shock are accelerated as a non-thermal population. This affects the estimate of the minimum electron energy and hence νm, the peak frequency of the afterglow spectrum. Here, we present Bayesian fitting to the observed data with a more natural electron energy distribution, in which the acceleration efficiency is a free parameter. Interestingly, the maximum likelihood solutions are found with radio flux below νm in the early phase, in contrast to previous studies that found the radio frequency always above νm. Therefore, the νm passage through the radio band could have been clearly detected for GW170817, if sufficient low-frequency radio data had been taken in early time. In the new solutions, the lowest energy of electrons is found close to equipartition with the post-shock protons, but only a small fraction (<10 per cent) of electrons are accelerated as non-thermal particles. The jet energy and interstellar medium density are increased by one to two orders of magnitude from the conventional modelling, though these are still consistent with other constraints. We encourage to take densely sampled low-frequency radio data in the early phase for future BNS merger events, which would potentially detect νm passage and give a strong constraint on electron energy distribution and particle acceleration efficiency.
Abstract Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
gravitational waves - binaries : close - stars: neutron
Simbad objects:
4
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