High energy emission from blazars constraints from neutrinos and x ray polarization

Abstract

Blazars are a subclass of active galactic nuclei (AGN), where the relativistic jet is closely aligned with the observer s line of sight. The physics governing these jets and their emission mechanisms remains an open question, making them a key focus of ongoing research. The broadband spectra of the blazars, characterized by a distinctive double-peaked structure, provide valuable newlineinformation about the underlying radiation processes within the jet. Two major milestones have driven signifcant advancements in this feld. The detection of neutrinos from the blazar TXS 0506+056 in 2017 and the launch of NASA s Imaging X-ray Polarimetry Explorer (IXPE) in 2021. newlineThe combination of neutrino observations and X-ray polarization studies with IXPE continues to enhance our understanding of blazar jets. This thesis presents an extensive study of the high-energy emission mechanisms of blazars. Typically, the emission processes in blazars are interpreted newlineusing two fundamental models. They are the leptonic model, associated with the energetic electrons in the jet, and the hadronic model, associated with the energetic protons. Key observables to distinguish these models newlineinclude variability analysis, neutrino emission, and X-ray polarization. In this work, we studied neutrino emission and X-ray polarization measurements to better understand blazar emission by integrating multi-wavelength and multi-messenger observations. Variability analysis aimed at understanding emission mechanisms has proven newlineto be complex. Given this, we prioritize neutrino detection from blazars as a primary observable. With the advent of neutrino detection, the feld of multi-messenger astrophysics has emerged, integrating observations from various cosmic messengers, including electromagnetic waves, neutrinos, newlinegravitational waves, and cosmic rays. The discovery of a neutrino from the blazar in 2017, which accompanied the source s increased x-ray activity marked a signifcant turning point.