http://arxiv.org/abs/1710.05448
We present details of our observational campaigns of electromagnetic transients associated with GW170817/GRB170817A using optical telescopes of Chilescope observatory and Big Scanning Antenna (BSA) of Pushchino Radio Astronomy Observatory at 110~MHz. The Chilescope observatory detected an optical transient of $\sim19^m$ on the third day in the outskirts of the galaxy NGC 4993; we continued observations following its rapid decrease. We put an upper limit of $1.5\times10^4$ Jy on any radio source of duration 10–60 s which may be associated with GW170817/GRB170817A. The prompt gamma-ray emission consists of two distinctive components – a hard short pulse delayed by $\sim 2$ seconds with respect to the LIGO signal and softer thermal pulse with $T\sim 10 $ keV lasting for another $\sim2$ seconds. The appearance of the thermal component at the end of the burst is uncharacteristic for GBRs. Both the hard and the soft components do not satisfy the Amati relation, making GRB170817A distinctively different from other short GRBs. Based on gamma-ray and optical observations we develop a model of prompt high-energy emission associated with GRB170817A. The merger of two neutron stars create an accretion torus of $\sim10^{-2} M_\odot$, which supplies the black hole with magnetic flux and confines the Blandford-Znajek-powered jet. We associate the hard prompt spike with the quasi-spherical break-out of the jet from the disk wind. As the jet plows through the wind with sub-relativistic velocity, it creates a radiation dominated shock that heats the wind material to tens of keV, producing the soft thermal component. After the break out the continuing jet regains collimation so that its emission, as well as early afterglows, is beamed away from the observer. The model explains both the off-axis viewing geometry and observations of the prompt emission.
A. Pozanenko, M. Barkov, P. Minaev, et. al.
Tue, 17 Oct 17
12/163
Comments: 19 pages, 11 figures, submitted to ApJL