Observations of Transient Events with Very-High-Energy Gamma-Ray Telescopes

Astrophysical events that evolve on short timescales (from milliseconds to years) are widely referred as transient events. In many cases, transient events are explosions or mergers of astrophysical objects that emit particles of all energies. This thesis focuses on very-high-energy (VHE; 100 GeV to 100 TeV) gamma rays, observed by the VERITAS telescope, to understand two types of transients, superluminous supernovae (SLSNe) and classical novae. In the first part, the background physics and technical approach of an imaging atmospheric Cherenkov technique deployed by VERITAS is reviewed in depth, including the analysis pipeline of VERITAS data, from camera data reduction to high level analysis output. In addition to supporting the ongoing work at VERITAS, the second part of this thesis describes the extensive effort to develop, commission and align the optical system of the prototype Schwarzschild-Couder telescope, also located at the VERITAS observatory. This new telescope provides an wider field of view and higher angular resolution compared with the conventional IACT design of current telescopes, and will join the next generation of VHE telescopes in the Cherenkov Telescope Array (CTA) project currently in development. The observation and analysis of two SLSNe is performed, on SN 2015bn and SN 2017egm, with both VERITAS and Fermi-LAT telescopes. The upper limit is reported on both events and is compared to a simple and a self-consistent model for parameter estimation. In addition, a population of sources were analyzed to estimate the future detection potential of new SLSNe with several gamma-ray observatories. Finally, the observation and analysis of several novae were performed. These sources were observed with VERITAS and Fermi-LAT. The observation of Nova Herculis 2021 is noteworthy in that the overlap of both observations may constrain the cutoff energy of the nova spectral model, providing a estimate for the maximum energy of the accelerated particles in the nova’s shock region.