THE GEORGE WASHINGTON UNIVERSITYDepartment of Physics Colloquium

Towards a Better Understanding of the GRB Phenomenon: a New Model for GRB Prompt Emission and its Effects on a New

Luminosity-Hardness Relation for Cosmology

Dr. Sylvain GuiriecNASA Goddard Space Flight Center

Gamma Ray Bursts (GRBs) are the most violent phenomenons in the Universe. They are believed to be

the footprint of black hole formation and the most promising sources for gravitational wave detections. The Fireball model (FB) is the most popular scenario to explain GRBs. In this theoretical framework, GRB central engines release highly relativistic jets. At early time, during the so-called prompt emission, FB predicts non-thermal and thermal-like emissions from accelerated particles and from the jet photosphere, respectively. Until recently, prompt emission spectra were considered as adequately fitted with the empirical Band function; however, its parameters are very often incompatible with the FB predictions for both the thermal and non-thermal components.

During the past years, we have been working on changing the prompt emission paradigm from a single component model (i.e., Band) to a multiple component one. Conversely to Band, the physical origin of the various components of our new paradigm are easier to assess: (i) a thermal-like component interpreted as the long-time predicted GRB jet photospheric emission, (ii) a non-thermal component compatible with synchrotron emission from accelerated electrons, and sometimes (iii) an additional non-thermal power law that is, however, more challenging to interpret. 

In this presentation, Dr. Guiriec will introduce this new paradigm through the reanalysis of some of the brightest and most popular GRBs observed with the NASA Fermi Gamma Ray Space Telescope. We will see how the new model dramatically changes the view that we have of those bursts. We will examine the implications of the new model for the GRB central engine and jet properties. Finally, we will introduce a new luminosity-hardness relation intrinsic to the non-thermal component of the new model that may eventually serve to calibrate GRBs as cosmological standard candles.

Dr. Guiriec will briefly explain why he thinks that misinterpretation of statistical analysis results as well as automation of analysis for phenomena that we do not understand well enough may have stop progresses in the GRB prompt emission research field, and how our approach differs from the previous one. Those considerations are particularly relevant in the world of Big Data where statistics are often the only scientific judgment.

TIME: 4:00-5:00 pm, Friday, September 26, 2014Refreshments will be offered at 3:45 pm

PLACE: Corcoran Hall 101, GWU

725 21st Street, N.W. (Between H and G Streets)