• astrophysical neutrinos
• blazar jet emission
• high energy gamma-rays
• neutrino telescopes

This PhD dissertation tackles the question of hadronic emission from the jets of blazars. Neutrinos are produced in the interactions of protons and neutrons with ambient photons and hence are a tell-tale sign of proton acceleration in the jets of AGN. The thesis focuses on analyzing the high energy activity of a sample of blazars selected for their spatial coincidence with candidate astrophysical neutrino events, and the characterization of their activity in high energy gamma-rays to understand their neutrino emission potential. Code has been developed to check for spatial and/or temporal overlap between blazars sampled from the Fermi-LAT 3FGL and 3FHL catalogs, and muonic neutrino events from IceCube with a high probability of being astrophysical in origin. Long-term light-curves of the blazars are obtained using Fermi-LAT data to identify their prominent flares. Their gamma-ray duty cycles and luminosities are also calculated, and the gamma-ray activity is related with neutrino emission using a one-zone lepto-hadronic model from Petropoulou et al. 2015. With this correlation, we are able to identify the minimum flare duration in gamma required to observe a neutrino in the km^3 Cherenkov telescopes around the world like IceCube and KM3NeT. The broad-band SEDs of a select few blazars are also analyzed and their gamma-ray SEDs compared during the flaring and quiescent periods.

A portion of the thesis deals with the time calibration of the two detector units of KM3NeT experiment (ARCA & ORCA) using atmospheric muons, and the data validation of 2 lines of KM3NeT/ARCA. As part of the calibration work, an approach is developed for inter-DOM time calibration that is independent of Monte Carlo and converges faster than the Monte Carlo-based strategy. It was tested on both KM3NeT/ARCA and KM3NeT/ORCA data with initial success. The data validation study involves the analysis of the ToT signals and PMT rates in KM3NeT/ARCA data and their comparison with Monte Carlo. Time-dependent and differential sensitivity studies for the KM3NeT/ARCA detector to the blazar TXS 0506+056 are also performed, using Monte Carlo simulation files.