On the nature of long GRB jets and how they can can be used to study the properties of "true" short GRBs.

Abstract:

A major questions in the study of GRBs is the composition of their

jets. The answer to this question has important implications on the energy

dissipation processes that leads to the emission of the high energy photons.

It can also provide clues for the type of the compact object that powers

the jet. In this talk I will discuss the properties of the jets in long GRBs

during their propagation inside the progenitor star. I will show the differences

between a hydrodynamic jet and a magnetic jet and how we can distinguish

between the two by the different times they break out of the star. The

breakout time of the jet leaves a distinctive mark on the duration distribution

of the long GRBs, or collapsars. As such, it can be used to better separate

the collapsar (long) GRBs from the non-collapsar (short) GRBs, producing

more homogeneous samples of non-collapsars which can be used to study

the properties of non-collapsars. The conclusions derived from the new

samples are somewhat different than those that are obtained from the currently

used samples, which are selected according to the traditional method of T90<2 sec.