Volume 628, August 2019
|Number of page(s)||9|
|Published online||29 July 2019|
On-axis view of GRB 170817A
INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
2 INFN – Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
3 Gran Sasso Science Institute, Viale F. Crispi 7, 67100 L’Aquila, Italy
Accepted: 1 July 2019
The peculiar short gamma-ray burst (SGRB) GRB 170817A has been firmly associated to the gravitational wave event GW170817, which has been unanimously interpreted as due to the coalescence of a double neutron star binary. The unprecedented behaviour of the non-thermal afterglow led to a debate over its nature, which was eventually settled by high-resolution VLBI observations that 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 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.
Key words: relativistic processes / gamma-ray burst: individual: GRB 170817A / stars: neutron / gravitational waves
© ESO 2019
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