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# 28th Texas Symposium on Relativistic Astrophysics

13-18 December 2015
International Conference Centre Geneva
Europe/Zurich timezone

## Thermal emission in GRB 101219B

14 Dec 2015, 14:00
21m
Level 2, Room 7&8 (International Conference Centre Geneva)

### Level 2, Room 7&8

#### International Conference Centre Geneva

17 Rue de Varembé, 1211 Geneva

### Speaker

Dr Josefin Larsson (KTH Royal Institute of Technology)

### Description

In recent years there has been growing evidence that emission from the photosphere of the jet contributes to the prompt emission in many GRBs. The photospheric emission is usually seen to coexist with a dominant non-thermal component. In this talk I will present an analysis of GRB 101219B, the second burst observed by Fermi GBM that is well described by pure blackbody emission. This burst also has a previously reported detection of a blackbody component at soft X-ray energies in the early afterglow observed by Swift. There is no smooth connection between the two blackbody components, ruling out the scenario that the late emission is due to high-latitude effects. The observed properties of the blackbody emission, together with the known redshift and our estimate of the radiative efficiency, makes it possible to calculate the properties of the jet within the standard fireball model. This yields an initial Lorentz factor of ~140 and a nozzle radius of ~ $3\times10^7$ cm. The latter value is close to the event horizon for a stellar-mass black hole and suggests that the jet has a relatively unobstructed path through the star.

### Primary author

Dr Josefin Larsson (KTH Royal Institute of Technology)