The breakthrough discovery of an astrophysical flux of high-energy neutrinos with the IceCube experiment in the year 2013 is a milestone in multi-messenger astrophysics. Identifying the sources of this cosmic flux remains to date a challenge. Traditional time-integrated searches for point-like sources of neutrinos could not single out sites of production because of large overwhelming backgrounds and weak neutrino signals. Several astrophysical scenarios are considered good as candidate neutrino emitters and, among those, a good fraction exhibit large variations in their non-thermal electromagnetic emission. This suggests that neutrino signals shall likely be variable in time as well. The IceCube Neutrino Observatory features the capability to observe the entire sky with a full duty cycle. This opportunity enables to continuously search for transient neutrino emissions and alert the astrophysical community with the lowest possible latency in case of detection of potential astrophysical neutrinos. To ensure a good efficiency in collecting possible neutrino flares, IceCube implemented an infrastructure that generates alerts whenever a significant flare is detected. The identification of the flaring Blazar TXS 0506+056 in association with a high-energy neutrino in 2017, demonstrates the potential of real-time multi-messenger studies. To increase the coverage of electromagnetic data during potential neutrino flares, the alerts are being distributed to the astrophysical community with a relatively low threshold on the significance. As a consequence, the majority of the alerts are expected to be due to statistical fluctuations of the background. This thesis focuses on the development of new strategies for a follow-up analysis of real-time IceCube alerts to single out a possible sample of pure astrophysical neutrino flares. The main challenge will be represented by mitigating the consequent loss in signal collection efficiency. This thesis work is divided into two main parts: 1) Offline reproduction of the results from historical triggers. This allows to achieve confidence with the statistical framework and the data analysis techniques used in this science area. It also allows to perform a survey of potentially interesting alerts as well as potentially critical results, such as the study of systematic uncertainties in the parameters and in the significance of the reconstructed alerts. 2)Development of new approaches to increase the signal-to-noise ratio of the events that contribute to the neutrino alerts. This study focuses on defining the typical characteristics of the detected transient events and provide a tool to outline the potentially interesting and significant flares from background fluctuations. The relevant parameters that can be used for this purposes are the signal-to-noise ratio of the events, their energy and their distance from the candidate sources. The definition of these criteria aims at selecting a sample of astrophysical pure alerts and at performing more detailed analyses in order to get a complete characterisation of the flares.

Follow-Up Analysis of Icecube Neutrino Alerts: new approaches to increase the signal-to-noise ratio

MANAO, ELENA
2021/2022

Abstract

The breakthrough discovery of an astrophysical flux of high-energy neutrinos with the IceCube experiment in the year 2013 is a milestone in multi-messenger astrophysics. Identifying the sources of this cosmic flux remains to date a challenge. Traditional time-integrated searches for point-like sources of neutrinos could not single out sites of production because of large overwhelming backgrounds and weak neutrino signals. Several astrophysical scenarios are considered good as candidate neutrino emitters and, among those, a good fraction exhibit large variations in their non-thermal electromagnetic emission. This suggests that neutrino signals shall likely be variable in time as well. The IceCube Neutrino Observatory features the capability to observe the entire sky with a full duty cycle. This opportunity enables to continuously search for transient neutrino emissions and alert the astrophysical community with the lowest possible latency in case of detection of potential astrophysical neutrinos. To ensure a good efficiency in collecting possible neutrino flares, IceCube implemented an infrastructure that generates alerts whenever a significant flare is detected. The identification of the flaring Blazar TXS 0506+056 in association with a high-energy neutrino in 2017, demonstrates the potential of real-time multi-messenger studies. To increase the coverage of electromagnetic data during potential neutrino flares, the alerts are being distributed to the astrophysical community with a relatively low threshold on the significance. As a consequence, the majority of the alerts are expected to be due to statistical fluctuations of the background. This thesis focuses on the development of new strategies for a follow-up analysis of real-time IceCube alerts to single out a possible sample of pure astrophysical neutrino flares. The main challenge will be represented by mitigating the consequent loss in signal collection efficiency. This thesis work is divided into two main parts: 1) Offline reproduction of the results from historical triggers. This allows to achieve confidence with the statistical framework and the data analysis techniques used in this science area. It also allows to perform a survey of potentially interesting alerts as well as potentially critical results, such as the study of systematic uncertainties in the parameters and in the significance of the reconstructed alerts. 2)Development of new approaches to increase the signal-to-noise ratio of the events that contribute to the neutrino alerts. This study focuses on defining the typical characteristics of the detected transient events and provide a tool to outline the potentially interesting and significant flares from background fluctuations. The relevant parameters that can be used for this purposes are the signal-to-noise ratio of the events, their energy and their distance from the candidate sources. The definition of these criteria aims at selecting a sample of astrophysical pure alerts and at performing more detailed analyses in order to get a complete characterisation of the flares.
2021
Follow-Up Analysis of Icecube Neutrino Alerts: new approaches to increase the signal-to-noise ratio
Multimessenger
Realtime astronomy
High energy neutrino
IceCube
Experimental physics
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12608/34066