Searching for multi-messenger counterparts to the sources in the H.E.S.S. Galactic Plane Survey
Date
2023
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Abstract
The High Energy Stereoscopic System (H.E.S.S.) Galactic Plane Survey (HGPS) has detected very-high-energy (VHE) gamma-ray emission from 78 sources in the Milky Way. These sources belong to different object classes (pulsar wind nebulae, supernova remnants or binary systems) and some of these sources remain unidentified. The gamma-ray emission of these objects may be of leptonic or hadronic origin and gamma-ray observations alone cannot distinguish between these two scenarios. The detection of neutrino emission would provide evidence for a hadronic scenario and fitting a combined synchrotron and inverse Compton model would provide evidence of a leptonic scenario in these objects.
MeerKAT surveyed the 1st and 4th quadrant of the Milky Way. There are 8 unidentified H.E.S.S. sources in the regions surveyed by MeerKAT. This process of searching for radio emission coincident with the unidentified sources in the HGPS can be expanded to the whole Galactic Plane once MeerKAT has surveyed it all. One unknown and two known H.E.S.S. sources (HESS J1843-033, HESS J1826-148 and HESS J1833-105) are modelled with a combined synchrotron and inverse Compton model using the MeerKAT radio data and H.E.S.S. VHE data. HESS J1843-033 is an unidentified source, HESS J1826-148 is a binary and HESS J1833-105 is a composite SNR. That these sources could be fit by a combined synchrotron and inverse Compton model suggest that they are leptonic in nature.
Based on the observed gamma-ray spectra we predict the neutrino emission of all the sources in the HGPS under the hypothesis that the emission is solely of hadronic origin. This prediction relies entirely on observation and is independent of the source class, the distance or the ambient target material. These predictions are used to create an empirical model for the neutrino emission of the Milky Way. This model can be used to search for neutrino emission from individual gamma-ray sources as well as testing for neutrino emission from potential source populations in the Milky Way. This model was then compared to the possible neutrino sources detected by ANTARES where 56 of the possible neutrinos were associated with the predicted neutrino emission but there is no significant correlation to the ANTARES neutrino candidates and the predicted neutrino emissions.
Description
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, University of the Witwatersrand, Johannesburg, 2022
Keywords
High Energy Stereoscopic System (H.E.S.S.), Galactic Plane Survey, Multi-messenger counterparts