Optimizing Galaxy Simulations using FGST Observations Andrew McLeod SULI Presentation August 13, 2009

GALPROP Simulates the gamma ray and cosmic ray sky given a set of initial conditions and physical parameters Allows a priori predictions to be compared to astronomical data

GALPROP Method Calculates a density field of cosmic rays given the distribution of cosmic ray sources (pulsars, supernova remnants) as an initial condition Computes the interaction of these cosmic rays with the interstellar gas field, radiation field, and magnetic field

“Propagation of cosmic rays: nuclear physics in cosmic ray studies”, Igor V. Moskalenko Source: http://galprop.stanford.edu/web_galprop/galprop_manual/manual2.html GALPROP

GALPROP Predicted gamma ray sky from Bremsstrahlung near our solar system

GALPROP

The Project Current parameter set optimized using EGRET data (1991-1994) Optimize to new Fermi data Simulated Fermi Data (>1 GeV, 1 yr)

GaDGET Calculates how well GALPROP models fit gamma ray sky detected by Fermi Fit-weights are computed for the energy bins of each component Calculates model’s statistical likelihood Produces sky-map of residual difference between fit-weight adjusted sky-map and Fermi data These fit weights don’t artificially fine tune data; they indicate how simulations must be changed

GaDGET

Optimization GALPROP parameters can be varied Galactic Dimensions Cosmic Ray Injection Spectra Source Distribution Diffusion Coefficient ~ 40 dimensional parameter space

Optimization Model Analysis (MAn) software developed for this project Analysis settings defined in a specification file Thirty-five different comparisons plotted Many user-defined setting; easily adaptable for future model optimization

Optimization

Results Previously used GALPROP parameters physically feasible, but not optimal Current optimized parameters imply that (relative to previous estimates): The diffusion coefficient governing the propagation of cosmic rays depends more heavily on momentum Cosmic ray source distribution peaks more sharply Gamma ray producing processes can occur farther away from the galactic disk

Potential Applications Indirect determination of Milky Way parameters Better understand the processes by which cosmic rays propagate Study extragalactic gamma ray spectrum

Acknowledgments I would like to express my deep gratitude to my mentor, Markus Ackermann, for helping me define and carry out this project, as well as to my co-workers Josh Lande and Keith Bechtol who helped in its implementation. Also, thanks to Steve Rock, SueVon Gee, Vivian Lee, and Elizabeth Smith for their stewardship of the SULI program. Finally, thanks to the DOE Office of Science and SLAC for sponsoring the SULI program.

Works Cited Moskalenko, Igor. “Modeling of the Galactic diffuse continuum gamma-ray emission” 6th INTEGRAL Workshop, Moscow, Russia. 2006. Moskalenko, Igor. “Propagation of Cosmic Rays and Diffuse Galactic Gamma Rays” Nuclear Data for Science and Technology, Santa Fe, New Mexico. 2004. Strong, Andrew. “GALPROP: a Cosmic-ray propagation and Gamma-ray code” Tools for SUSY, Annecy, France. 2006.