Very High Energy Astrophysics with VERITAS

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Gamma-ray astronomy probes the extreme physics of systems such as the black holes at the centers of active galaxies or the remnants of supernova explosions that end the lives of many giant stars. These systems emit radiation throughout the electromagnetic spectrum and hundreds are now detectable in the very-high-energy gamma-ray energy band observable by ground-based detectors. The VERITAS gamma-ray observatory, located at the F. L. Whipple Observatory in Arizona, has been and continues to be a key driver of the field’s expansion, making discoveries that, combined with the information obtained from telescopes operating at multiple wavelengths, has significantly increased our understanding of the most energetic processes in the Universe. The VERITAS team at the University of Minnesota, involving postdoctoral and student researchers, focuses on investigations that can help decipher how active galaxies power the emission of gamma rays and the possible links to the origin of ultra-high-energy cosmic rays and astrophysical neutrino production, two outstanding questions in the field. The team is also developing calibration techniques for the prototype Schwarzschild-Couder Telescope envisaged as a component of the next-generation Cherenkov Telescope Array. Through this effort, a citizen science project via Zooniverse.org provides direct opportunities for public participation in gamma-ray related science via crowdsourced classifications of VERITAS images that will improve the classification of astrophysical objects. Ground-based very-high-energy (VHE) gamma-ray astrophysics has matured as a field in the last decade, expanding the VHE catalog from a handful to over 200 objects across a wide range of source classes that represent the most extreme phenomena in the Universe. VERITAS observations combined with a wealth of multi-wavelength data from radio to X-ray, and especially high-energy gamma rays from NASA’s Fermi-LAT satellite, has significantly increased our understanding of the most energetic processes in the Universe. The work carried out under this grant is crucial to maintaining the sensitivity of VERITAS to maximize the science return on data taking campaigns across the spectrum as well as with multi-messenger observatories. New analysis methods are targeted that boost sensitivity to weak sources, implement modifications that monitor and account for changes in the overall detector throughput, and address systematic uncertainties at the highest recorded energies by the observatory. These efforts will enable discoveries of new VHE emitting active galactic nuclei (AGN) and observations of known VHE blazars with the goal to better characterize the so-called blazar sequence that postulates an inverse relationship between blazar luminosity and peak synchrotron emission frequency potentially due to cosmic evolution. It will also enable the investigation of blazar spectra at high optical depth where absorption features due to gamma-ray interactions on the extragalactic photon fields becomes important. Results from this work can also be used to elucidate the astrophysics behind gamma-ray emission in blazars and its links to the origin of ultra-high-energy cosmic rays and astrophysical neutrino production.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.