Gravitational-wave Memory from a Propagating Relativistic Jet: A Probe of the Interior of Gamma-Ray Burst Progenitors

It is believed that the relativistic jets of gamma-ray bursts (GRBs) should initially propagate through a heavy envelope of the massive progenitor stars or through merger ejecta formed from compact binary mergers. The interaction of a jet with a stellar envelope or merger ejecta can lead to the deceleration of the head material of the jet and simultaneously the formation of a hot cocoon. However, this jet-envelope/ejecta interaction is actually undetectable with electromagnetic radiation and can only be inferred indirectly by the structure of the breakout jet. Therefore, as a solution to this phenomenon, we suggest the jet-envelope/ejecta interaction can produce a gravitational-wave (GW) memory of an amplitude of , which could be detected with some future GW detectors sensitive in the frequency range from sub-Hertz to several tens of Hertz. This provides a potential direct way to probe the jet propagation and then the interior of the GRB progenitors.