  Long Gamma-Ray Bursts (GRB) relativistic jets are surrounded by hot cocoons
which confine jets during their punch out from the progenitor star. These
cocoons are copious sources of X-ray photons that can be and are
inverse-Compton (IC) scattered to MeV--GeV energies by electrons in the
relativistic jet. We provide detailed estimates for IC flux resulting from
various interactions between X-ray photons and the relativistic jet, and
describe what we can learn about GRB jets and progenitor stars from the
detection (or an upper limit) of these IC scattered photons.

High Energy Astrophysical Phenomena