RUI: WoU-MMA: From Origin to Observation: Understanding Extragalactic Gamma-rays from Blazars

Blazars, one of the most extreme objects in the observed local Universe, occur when the jet emitted from a supermassive black hole is aligned in the general direction of the Earth. An anticipated astrophysical accelerator for cosmic rays at the highest energies, very-high-energy (VHE) gamma-rays are observed coincident with these objects and provide a means to study the underlying processes.

This award supports scientists at the California State University - East Bay (CSUEB) to utilize observations of VHE gamma-rays with the VERITAS telescope, located south of Tucson, Arizona, to study the behavior of the most energetic galaxies within the local Universe. The program provides the opportunity for hands-on experience in leading particle astrophysics research for undergraduates at CSUEB.

Using gamma-ray observations of extremely energetic galaxies, the students will study the different processes that can occur to high energy photons as they travel from the galaxy to the Earth and apply what they learn to the large-scale structure of the Universe between Earth and the energetic galaxy. Relatedly, the program will advance target-of-opportunity real-time follow-ups of astrophysical events of interest for current and future VHE gamma-ray observatories.

Very high energy photons and ultra-high-energy cosmic-rays (Energy > 1 PeV) ejected by a blazar have the potential to initiate a cascade process as they traverse the extragalactic distance from source to observer. Due to these interactions, the observed gamma-ray flux is not strictly that which is emitted at the source. Instead, the observed flux may be a combination of the absorbed intrinsic gamma-ray flux (primary emission) and the up-scattered gamma-rays that result from the cascade process along the extragalactic path (secondary emission).

The portion of the gamma-ray flux resulting from cascade emission which continues to travel along the original line of sight depends on the magnitude of the intergalactic magnetic field. The proposed astrophysical mechanisms for generating large-scale magnetic fields predict little magnetic flux inside regions of lower integrated mass density, also known as voids.

Studying the location of gamma-ray emitting galaxies with respect to cosmic voids can provide insight on the strength of the magnetic field inside of voids. This project advances the goals of the NSF Windows on the Universe Big Idea.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.