This webpage is kept for archival purposes only and is no longer updated or maintained.

The 2009 Fermi Symposium

Constraining GRB Jet Composition with Fermi Data

Bing Zhang


The smooth Band function spectrum of GRB 080916C significantly constrains the composition of the GRB ejecta. In particular, the lack of a thermal emission component expected from the fireball photosphere suggests that the ejecta was not launched as a "fireball" from the central engine. The outflow has to be Poynting-flux dominated at the central engine, and very likely in the emission region as well. A new model for GRB prompt emission in the Poynting-flux dominated regime is proposed.