The angular structure of ultra-relativistic jets in gamma-ray bursts emerges from their interaction with the confining medium, which the jets must propagate through and break out of to produce the burst of gamma-rays. Important role in shaping up the angular structure is played by the composition (baryonic Vs magnetically dominated) of these outflows, which remains an open question. Several semi-analytical works and numerical simulations are devoted to understanding the basic “universal” structure of GRB jets, making it a very active topic of research. Complementary information comes from the afterglows produced by misaligned jets, and a golden opportunity was presented by the afterglow of GW170817 — the first multi-messenger binary neutron star merger with coincident gravitational wave and electromagnetic detections.
In this talk, I will discuss how our understanding of GRB jets have evolved over the years, moving from uniform top-hat jets to jets with angular structure. Recent hydrodynamic numerical simulations are suggesting some “universal” features that are present in the angular structure of these jets. However, they do differ in important ways from their MHD counterparts. I will show how the afterglow emission derived from parameterized phenomenological structure models, as well as those obtained from numerical simulations, are used to obtain useful constraints. Here, I will particularly emphasize the afterglow modeling of GW170817. In the end, I will present a systematic way to understand the diversity in GRB afterglows from misaligned jets, where I will also highlight differences between steep and shallow jets.