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Photospheric Polarization Signatures of Long Gamma Ray Bursts

Photospheric Polarization Signatures of Long Gamma Ray Bursts

Wednesday, April 3, 2019 at 4:00 pm
304 Weniger
Tyler Parsotan

An outstanding issue in the study of Gamma Ray Bursts (GRBs) is determining the radiation mechanism at play in the GRB jet that gives rise to their high energy prompt emission. The prompt emission can be explained under the framework of either the synchrotron shock model or the photospheric emission model. The SSM invokes relativistic shells with varying speeds that have been emitted by the central engine of the GRB; these collide with one another, release synchrotron radiation, and thus produce the detected non-thermal emission. The photospheric model on the other hand is based on the modification of a thermal spectrum of advected radiation that becomes non-thermal as it propagates through and eventually escapes the GRB jet.

One of the most direct ways of distinguishing between these models is from high accuracy polarization measurements of GRB prompt radiation. Thus, in order to maximize scientific output of future observatories, we need to have theoretical predictions of the polarization signatures of these radiation models for GRBs.

We use our Monte Carlo radiation transfer (MCRaT) code to simulate the prompt emission from a variety of Long GRBs hydrodynamic simulations. Under the framework of the photospheric model, we predict and characterize the spectrum, variability, and expected polarization signature for a variety of stellar progenitors and jet engine profiles.


Tyler is the first born child in a family of immigrants from the small Caribbean island nation Trinidad and Tobago. He is from Shirley, NY, where he graduated high school at the age of 16. He went on to attend Embry-Riddle Aeronautical University in Daytona Beach, FL with the major of Space Physics. As an undergraduate, Tyler studied electron heating in the upper atmosphere, as well as the use of Bayesian statistics to extract stellar parameters from stellar models. Additionally, as an intern at NASA's Johnson Space Center he worked on determining when parts on the International Space Station would break. Tyler graduated from Embry-Riddle in 2015 and currently attends Oregon State University as a doctoral candidate in the Department of Physics under the direction of Davide Lazzati.

As a graduate student,Tyler was awarded two honorable mentions in the NSF’s Graduate research fellowship and the EAPSI fellowship, which allowed him to travel to Japan to conduct some of his research at RIKEN. Additionally, he was recently accepted to the KAVLI astrophysics summer school on Galaxy formation, at the Center for Computational Astrophysics, where he studied the compactness of simulated galaxies. Beyond his research, Tyler leads the OSU Astronomy Club, the Astronomy Open Houses, and enjoys rock climbing, scuba diving, skiing and hiking.