Two-component Jets of GRB 160623A as Shocked Jet Cocoon Afterglow

Abstract

Two components of jets associated with the afterglow of the gamma-ray burst GRB 160623A were observed with multi-frequency observations including long-term monitoring in a sub-millimetre range (230 GHz) using the SMA. The observed light curves with temporal breaks suggests on the basis of the standard forward-shock synchrotron radiation model that the X-ray radiation is narrowly collimated with an opening angle θ n,j <∼ 6 • whereas the radio radiation originated from wider jets (∼ 27 • ). The temporal and spectral evolutions of the radio afterglow agree with those expected from a synchrotron radiation modelling with typical physical parameters except for the fact that the observed wide jet opening angle for the radio emission is significantly larger than the theoretical maximum opening angle. By contrast, the opening angle of the X-ray afterglow is consistent with the typical value of GRB jets. Since the theory of the relativistic cocoon afterglow emission is similar to that of a regular afterglow with an opening angle of ∼ 30 • , the observed radio emission can be interpreted as the shocked jet cocoon emission. This result therefore indicates that the two components of the jets observed in the GRB 160623A afterglow is caused by the jet and the shocked jet cocoon afterglows.

Accounting for Selection Bias and Redshift Evolution in GRB Radio Afterglow Data

“…We look at the log E iso and log T * 90 for a sample of 80 GRBs with observed radio afterglow published in the literature [80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98]. Values of log E iso are taken from the literature.…”

Jet-cocoon geometry in the optically dark, very high energy gamma-ray burst 201216C

“…Observations of some GRB afterglows have shown evidence of a second forward shock component originating from a wider outflow (Resmi et al 2005;Starling et al 2005;Racusin et al 2008;Kamble et al 2009;Filgas et al 2011;Van der Horst et al 2014;Lan et al 2018;Chen et al 2020). This second component is sometimes interpreted as a cocoon (e.g.…”

“…This second component is sometimes interpreted as a cocoon (e.g. Chen et al 2020). Cocoons are often suggested to explain why GRB jets are so highly collimated.…”

ALMA Host galaxy observation of the off-axis Gamma-Ray Burst XRF020903

“…Racusin et al 2009). Cocoon structures surrounding the GRB jets were identified to be similar to those of AGNs (Izzo et al 2019;Chen et al 2020). Similar to the unification model of AGNs, observing GRB jets at the various viewing angles can provide GRBs, XRFs, off-axis orphan GRB afterglows and energetic stellar explosions (e.g.…”