Abstract
Gamma-Ray Analysis of the Most Energetic Blazars to Probe the Cosmos
Yashika Batra (Evergreen Valley High School)
Je-Won Im (Choate Rosemary Hall)
Nathan Nguyen (Atholton High School)
Mentor: Dr. Olivier Hervet (UC Santa Cruz)
Measurements of the Extragalactic Background Light (EBL), a photon field consisting of all infrared to optical light emitted in the Universe since the epoch of reionization, are crucial to understanding cosmological evolution. Direct measurements of the EBL are difficult due to foreground emissions, so it is measured indirectly off of its gamma ray attenuation of blazars. This method relies on assumptions on blazar intrinsic spectra, so the Santa Cruz Institute of Particle Physics (SCIPP) conducted normalization on indirectly measured EBL models. The initial normalizations of blazars from the Fermi-LAT Fourth Source Catalog Data Release 2 (4FGL-DR2) using 10 years of Fermi-LAT resulted in outlier normalization values disagreeing with EBL models and biases towards low EBL absorption. As the outlier values could have resulted from artifact or anisotropic characteristics, we analyzed these sources to improve EBL normalizations, and also conducted analyses of high-opacity 4FGL-DR2 sources to investigate the low-absorption biases. Because the Fermi-LAT only observes up to a few TeV, we also appended data from the database of the MAGIC Atmospheric Cherenkov Imaging Telescopes which observe up to ~10 TeV to provide SCIPP with very-high-energy data. To reduce the time of procedures, we developed a python module that utilized results from spectral analyses to find optimal models and values of the normalization factors and redshifts. By estimating the normalization factor for a large number of blazars observed by Fermi-LAT and more, this study will contribute to the creation of an accurate map of EBL density.
