A Multimessenger Approach to Neutrino Astronomy
Tung, Chun Fai
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The discovery of a diffuse astrophysical neutrino flux by Icecube Neutrino Observatory marked the beginning of neutrino astronomy. Since then, great efforts have been poured into the search for the sources of these cosmic neutrinos. Although no source has been resolved, evidence of neutrino emission from the blazar TXS 0506+056 was found by a multimessenger observation campaign, which was triggered by the detection of an neutrino event candidate IC170922A. This result showcased the potential of the multimessenger approach to neutrino astronomy. In this thesis, I will present three works that were developed based on the idea of multimessenger astronomy. The first one is FIRESONG, an open source software for simulating extragalactic neutrino sources and their fluxes, which allows one to translate the diffuse neutrino flux into limits in different analyses, including analyses of very-high-energy gamma rays. The second one is the update performed on IceCube's realtime neutrino alert system, which improves the rate, angular resolution, and signal purity of the alerts, hence facilitating observers from all disciplines to follow up on the neutrino events. The third one is a search for periodic neutrino emission from X-ray binaries. Binaries with a compact object have long been considered as galactic neutrino sources. The method for this search involves using the orbital periods measured by electromagnetic (EM) observations to improve the sensitivity. The search was performed on 55 XRBs with more than 1.5 million neutrino events collected by IceCube from 2011 to 2018, and no significant emission was found. Upper limits on the neutrino flux from each XRB were calculated. The upper limits of the two XRBs were compared with the neutrino flux predicted by phenomenological models.