The on-axis view of GRB 170817A. (arXiv:1905.01190v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Salafia_O/0/1/0/all/0/1">O. S. Salafia</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ghirlanda_G/0/1/0/all/0/1">G. Ghirlanda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ascenzi_S/0/1/0/all/0/1">S. Ascenzi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ghisellini_G/0/1/0/all/0/1">G. Ghisellini</a>
The peculiar short gamma-ray burst GRB 170817A has been firmly associated to
the gravitational wave event GW170817, which has been unaninmously interpreted
as due to the coalescence of a double neutron star binary. The unprecedented
behaviour of the non-thermal afterglow led to a debate about its nature, which
was eventually settled by high-resolution VLBI observations, which strongly
support the off-axis structured jet scenario. Using information on the jet
structure derived from multi-wavelength fitting of the afterglow emission and
of the apparent VLBI image centroid motion, we compute the appearance of a GRB
170817A-like jet as seen by an on-axis observer and we compare it to the
previously observed population of SGRB afterglows and prompt emission events.
We find that the intrinsic properties of the GRB 170817A jet are representative
of a typical event in the SGRB population, hinting at a quasi-universal jet
structure. The diversity in the SGRB afterglow population could therefore be
ascribed in large part to extrinsic (redshift, density of the surrounding
medium, viewing angle) rather than intrinsic properties. Although more
uncertain, the comparison can be extended to the prompt emission properties,
leading to similar conclusions.
The peculiar short gamma-ray burst GRB 170817A has been firmly associated to
the gravitational wave event GW170817, which has been unaninmously interpreted
as due to the coalescence of a double neutron star binary. The unprecedented
behaviour of the non-thermal afterglow led to a debate about its nature, which
was eventually settled by high-resolution VLBI observations, which strongly
support the off-axis structured jet scenario. Using information on the jet
structure derived from multi-wavelength fitting of the afterglow emission and
of the apparent VLBI image centroid motion, we compute the appearance of a GRB
170817A-like jet as seen by an on-axis observer and we compare it to the
previously observed population of SGRB afterglows and prompt emission events.
We find that the intrinsic properties of the GRB 170817A jet are representative
of a typical event in the SGRB population, hinting at a quasi-universal jet
structure. The diversity in the SGRB afterglow population could therefore be
ascribed in large part to extrinsic (redshift, density of the surrounding
medium, viewing angle) rather than intrinsic properties. Although more
uncertain, the comparison can be extended to the prompt emission properties,
leading to similar conclusions.
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