Thesis Dissertation Defense

Thesis Dissertation Defense

Studying Millisecond Pulsars and Pulsar Tails in the Very-High-Energy Gamma-ray Regime with VERITAS


June 27, 2022 - 2:00pm to 3:00pm



Dissertation Defense Room, 4th floor of Price Gilbert Library, Room 4222


Georgia Institute of Technology

Abstract: 'Years have passed since the first detection of pulsed very-high-energy (VHE; E >100 GeV) gamma-rays from the Crab pulsar with VERITAS, yet much is still unresolved in relation to the nature of pulsar emission mechanisms and how they interact with the surrounding medium. No completely satisfactory model has been produced that can accurately describe all aspects of the pulsed gamma-ray emission observed from the Crab and other pulsars. Understanding the properties of VHE emission detected in observations made by many different experiments still poses a significant challenge. The crux of the issue remains; is the Crab pulsar unique, or do other pulsars also exhibit the same behavior in the VHE regime, and, in either case, what are the underlying mechanisms? To try and answer this question, while also learning more about the pulsar population and the physics of VHE gamma-ray production, this work will present the results of a search for pulsed emission in the VHE band from six Millisecond Pulsars (MSPs) in the archival VERITAS data-set, the first such survey of MSPs, and the most sensitive VHE measurements ever made for the targets. I test to see if significant pulsed emission is detected, report the observed VHE pulsed flux and gamma-ray conversion efficiency of these MSPs, to determine if there is an appearance of a VHE flux element at these energies, for the sources studied here. As the analyses result in non-detections, in every case, upper limits are placed on the aforementioned quantities. The upper limits are compared with a modern, comprehensive pulsar model energy spectrum and are found to be compatible with the proposed theoretical scenario, although we are limited by a lack of target-specific predictions. Pulsars are also sources of non-pulsed gamma-rays. However, at the time of writing, there has been no decisive detection of the TeV emission expected by current models from any pulsar tail that is also seen in the X-ray or radio bands. An observational campaign has been carried out by VERITAS to hunt for VHE gamma-ray emission from the candidate tail regions associated with three nearby pulsars (PSR B0355+54, PSR J0357+3205 and PSR J1740+1000) that move supersonically and exhibit significant X-ray tails. The results of this analysis provides quantification of the TeV flux and luminosity, from the tail regions of the targets, for comparison with other pulsar wind nebulae observations and the predictions of modern pulsar tail models. The results of this search also provide guidance for the selection of additional candidates, and quantifying the properties of pulsar tails, for new pulsars tails that may be observed in the VHE regime.'