Multi-messenger search for galactic PeVatron with HAWC and IceCube

Abstract

In recent years, many advancements in astrophysics have brought astrophysicists new tools to study the universe. Specifically, the discovery of astrophysical neutrinos by the IceCube Neutrino Observatory and Gravitational waves by the LIGO/Virgo collaboration has started the era of multi-messenger astronomy. Scientists can finally use messengers other than electromagnetic waves to study astrophysical phenomena. With the addition of new messengers, it is crucial that data from multiple instruments and messengers can be jointly analyzed through a unified framework using one physics model. Many efforts have been put into jointly analyzing electromagnetic waves of different wavelengths from different instruments, but the ability to jointly fit other messengers to a single physics model is still missing. In this work, we present a method to jointly analyze data from HAWC Gamma-ray Observatory and IceCube Neutrino Observatory by using a newly developed IceCube likelihood software called i3mla and the existing HAWC likelihood software called HAL. Together with the Multi-Mission Maximum Likelihood framework (3ML), we are able to jointly fit the gamma-ray emission model and neutrino emission model simultaneously with the HAWC gamma-ray and IceCube neutrino data.

We apply the method to search for Galactic PeVatrons. Galactic PeVatrons are sources of PeV galactic cosmic rays. When the cosmic ray interacts with nearby material, it will produce both gamma rays and neutrinos with the same morphology and spectral shape. While gamma rays could also be produced from other interactions, neutrinos can only be produced by hadronic interactions of the cosmic ray. Therefore, it is natural to search for neutrino emissions from gamma-ray sources. We first perform a search for neutrino emissions from the 12 known gamma-ray sources detected by LHAASO. No significant detection was found and we put constraints on the neutrino emission on the sources. Second, a more detailed multimessenger search of Galactic PeVatrons candidates using simultaneously the HAWC data and IceCube neutrino data is conducted. We model the gamma-ray emission using the HAWC data and jointly fit a unified model to both the gamma-ray and neutrino data. No significant detection was found and we put constraints on the fraction of the gamma rays due to hadronic interactions.