Session E02: Gamma Rays

Astrophysical transformations in 12 years of the Fermi Gamma-ray Space Telescope

In Fermi’s first 12 years, the mission has changed our understanding of the physical processes going on in extreme objects throughout the Universe. The Fermi instruments observe the entire sky multiple times a day and cover orders of magnitude in energy, deepening the view over time and catching changes in the sky as they occur. Since its launch Fermi has discovered thousands of new sites of gamma-ray emission ranging from a variety of stellar explosions and remnants to emission from supermassive black holes and vast glowing regions of the Milky Way. Gamma-ray emission gives us a unique picture of dramatic astrophysical transformations. I’ll share recent highlights from the dynamic gamma-ray sky and opportunities for the future.   

Recent Results from the HAWC Gamma Ray Observatory

The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory in the high mountains of Mexico is giving us a new view of the TeV sky. Unlike Imaging Atmospheric Cherenkov Telescopes (IACTs), HAWC operates 24hrs/day with over a 95{\%} on-time and observes the entire overhead sky (\textasciitilde 8sr over the course of the day). This talk will present an overview of recent HAWC results showing our updated sky catalog, our view of the highest energy gamma-ray sky (including sources above 50 and 100 TeV), first observations of the jets of a micro-quasar and a summary of recent observations of galactic Pevatrons. In addition, we will present recent limits on primordial black holes, Lorentz invariance violation and multi-messenger observations.   

Unassociated Candidate TeV Sources from HAWC

In 2017, the High Altitude Water Cherenkov (HAWC) Collaboration presented the 2HWC catalog from 508 days of data, which included 16 candidate sources farther than 1 degree from any previously identified TeV source. We examined these candidate sources over time and updated their locations and extensions. Now, with nearly triple the amount of data (1523 days), we compare our findings to that of the newly released 3HWC catalog and analyze the morphology and energy spectra of some of these candidate sources in more detail.   

Combined Energy Spectrum of the Supernova Remnant IC 443

The supernova remnant IC 443 is a very well-studied source and a clear example of interaction with a molecular cloud. We consider the highest energy emissions of the source using data collected with the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory. We combine the TeV data from HAWC with radio, X-ray, and gamma-ray data from other experiments in order to produce a physical model including both leptonic and hadronic emission.   

Analysis of Te-REX Sources Using HAWC Observatory Data

Te-REX (TeV-emitting Radio-emitting X-Ray) sources are a sample of high-energy peaked BL Lac (HBL) objects selected from the larger REX catalogue because they are thought to be TeV-emitting. We focus on six sources identified as visible by Fermi-LAT (Large Area Telescope). Using data collected with the High Altitude Water Cherenkov (HAWC) Observatory, we aim to get a better picture of the energy emitted by these sources and their flux at the Earth’s surface. Exploring the highest energy emissions of these sources would allow us to get a more complete idea of the overall energy emissions of these specific sources. We calculate upper limits on all six sources to gain a better picture of their ability to emit in such a high energy range. We extrapolate the fluxes for these sources and identify which sources to further research.   

Gamma Ray Analysis of the Most Energetic Blazars to Probe the Cosmos

Proper measurements of the Extragalactic Background Light (EBL), the radiation field of all infrared to light emitted in the Universe since reionization, are key to understanding the cosmic makeup and evolution of the universe. However, its direct measurement is difficult due to bright foreground emissions. An alternative method is to indirectly probe the EBL from its interaction with gamma rays emitted by blazars. The Fermi-LAT and H.E.S.S collaborations proposed using a scaling factor alpha to normalize EBL density based on a previously existing model. However, numerous ``problematic'' sources that deviate more than a discrepancy of 3 sigma from an EBL model were present in Fermi-LAT's 4FGL-DR2 catalog, which contained 10 years of data. We performed a new gamma ray analysis on 12 years of Fermi-LAT observations, focusing on ``problematic'' and bright sources. The changes on the scaling factor alpha derived from our analysis resolve the issue for most of the ``problematic sources'', while creating a new outlier from our ``bright sources'' sample. By estimating the factor alpha for a large number of blazars observed by the Fermi Large Area Telescope (Fermi-LAT), this study will contribute to the creation of a map of the density of the EBL.