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Free keywords:
Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE, Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM,General Relativity and Quantum Cosmology, gr-qc
Abstract:
In this paper, we compute and analyze synthetic radio images of gamma-ray
bursts and kilonova afterglows. For modeling the former, we consider
GRB170817A-inspired set of parameters, while for the latter, we employ ejecta
profiles from numerical-relativity simulations. We find that the kilonova
afterglow sky map has a doughnut-like structure at early times that becomes
more ring-like at late times. This is caused by the fact that the synchrotron
emission from electrons following Maxwellian distribution function dominates
the early, beamed, emission while emissions from electrons following power-law
distribution is important at late times. For an on-axis observer, the image
flux centroid moves on the image plane initially away from the observer. Flux
centroid displacement The image sizes, we find, are the largest for equal mass
merger simulations with the soft equation of state. The presence of a kilonova
afterglow affects the properties inferred from the source sky map even if the
gamma-ray burst afterglow dominates the total flux density. The main effect is
the reduction of the mean apparent velocity of the source, and an increase in
the source size. Thus, neglecting the presence of the kilonova afterglow may
lead to systematic errors in the inference of gamma-ray burst properties from
the sky map observations. Notably, at the observing angle inferred for
GRB170817A the presence of kilonova afterglow would affect the sky map
properties only at very late times $t\gtrsim1500\,$days.
