Gamma rays are photons (particles of light) with energies higher than a few MeV (106 eV), millions of times higher than visible light (2-3 eV). Lower energy photons are generated mainly from the interactions of leptonic particles (electrons and positrons). High-energy astrophysical gamma rays are generated by both leptonic particles (via interactions with radiative environments) and hadronic particles, such as protons (via inelastic collisions with the stellar medium). By studying high-energy gamma rays originating from astrophysical objects, we can understand the dynamics of the interactions of hadronic particles that are accelerated in these objects. This is especially important for helping us to identify the sources of cosmic rays (energetic charged particles arriving from outside the solar system), which are overwhelmingly composed of hadronic particles.
Detection of very-high-energy gamma rays
Very-high-energy (VHE) gamma rays, those with energies higher than 100 GeV (1011 eV), are relatively rare. To detect a large enough number of gamma rays for study, detectors must have an enormous effective collection area, on the order of 10,000 m2 or larger. Such detectors observe the showers of secondary particles that occur when the primary gamma ray interacts with and is destroyed by the atmosphere. Imaging atmospheric Cherenkov telescopes (IACTs) accomplish this by observing the fast Cherenkov light emitted by the secondary particles in the shower. This light is focused onto a camera comprised of fast photo-sensitive detectors, such as photomultiplier tubes. By measuring the number of photons and their arrival time distribution, the direction and energy of the gamma rays can be determined. Most IACTs currently operate in an array configuration with 2-5 telescopes, which improves background rejection and signal reconstruction. From the first detection of a gamma-ray source in 1989, the VHE catalogue has grown to include more than 200 sources.
My research in gamma rays
I joined the VERITAS (Very Energetic Radiation Imaging Telescope Array) IACT collaboration in 2010. My science interests in VHE gamma rays focus on studying the accelerators of hadronic particles in our Galaxy, including both supernova remnants and unidentified sources. Recently I extended my interests to include follow-up observations of high-energy neutrino events. I have also contributed to provide simulation data for the VERITAS analysis, and to the performance studies of VERITAS array. I have served as co-chair of the Galactic working group and the simulation working group for VERITAS. VERITAS is a state-of-the-art IACT and will provide one of the most sensitive gamma-ray observations until the next generation gamma-ray observatory, the Cherenkov Telescope Array, comes online.
VERITAS collaboration: Located at Tucson, Arizona, VERITAS is an array of four imaging atmospheric Cherenkov telescopes.