Observation of high-energy neutrinos from the Galactic plane (2307.04427v1)

Abstract: The origin of high-energy cosmic rays, atomic nuclei that continuously impact Earth's atmosphere, has been a mystery for over a century. Due to deflection in interstellar magnetic fields, cosmic rays from the Milky Way arrive at Earth from random directions. However, near their sources and during propagation, cosmic rays interact with matter and produce high-energy neutrinos. We search for neutrino emission using machine learning techniques applied to ten years of data from the IceCube Neutrino Observatory. We identify neutrino emission from the Galactic plane at the 4.5$\sigma$ level of significance, by comparing diffuse emission models to a background-only hypothesis. The signal is consistent with modeled diffuse emission from the Galactic plane, but could also arise from a population of unresolved point sources.

• The paper reports a 4.5σ detection of neutrino emission from the Galactic plane, supporting models of cosmic-ray interactions in the Milky Way.
• It employs advanced deep learning and statistical methods on a decade of IceCube data to enhance angular resolution and signal retention.
• The findings imply that Galactic neutrinos contribute 6–13% of the all-sky astrophysical flux, opening avenues for identifying individual sources.

Observation of High-Energy Neutrinos from the Galactic Plane

The paper "Observation of high-energy neutrinos from the Galactic plane" presents the findings of the IceCube Collaboration regarding the origin of high-energy neutrinos associated with cosmic ray interactions within the Milky Way. Using a decade's worth of data from the IceCube Neutrino Observatory, the research outlines the search strategies and results that indicate the presence of neutrino emission from the Galactic plane.

The paper tackles the long-standing enigma of high-energy cosmic rays, which are atomic nuclei that impact the Earth's atmosphere from all directions due to deflection by interstellar magnetic fields. As a result, tracing them back to their origins has been challenging. High-energy neutrinos, which originate from interactions of cosmic rays with matter, provide a more direct probe of cosmic ray sources in the Galactic plane, owing to their minimal interaction with surrounding matter compared to photons.

Utilizing advanced machine learning techniques to analyze the IceCube data, neutrino emission from the Galactic plane is detected with a significance of 4.5σ. This discovery is consistent with predictions of diffuse neutrino emission arising from cosmic-ray interactions in the Galaxy, modeled primarily through decay processes involving pions. The findings suggest that while diffuse emission is a contributing factor, the observed neutrinos may also emanate from unresolved point sources within the Milky Way, such as supernova remnants and pulsar wind nebulae.

Methodological Insights

The IceCube collaboration employed several state-of-the-art analytical techniques, notably leveraging deep learning tools, to enhance sensitivity to neutrino interactions. Comparing various models of Galactic diffuse neutrino emission—such as the π^0 and KRA_γ models—allowed the team to discern the spatial patterns of potential neutrino sources. Model-to-model predictions facilitated the identification of potential emission signatures corresponding to interactions in the interstellar medium or unresolved astrophysical sources.

The deep learning approach, using convolutional neural networks, marks a significant improvement over traditional methods, retaining more signal events and offering superior angular resolution for cascade events. This is crucial given the existence of an overwhelming background from atmospheric neutrinos and muons.

Results and Implications

The results presented in the paper include significant evidence of neutrino emission from the Galactic plane, which encompasses various emission hypotheses tested across the sky. The analyses reveal a best-fit consistent with modeled diffuse emission from the Galactic plane, showcasing a significant excess from this source compared to background-only expectations.

These observations have notable implications:

• Validation of the Cosmic-Ray Interaction Model: The detection supports existing models of cosmic-ray interactions within the Galaxy, previously inferred from gamma-ray data. This marks a substantial step toward understanding cosmic ray propagation and secondary neutrino production mechanisms.
• Contribution to the Astrophysical Neutrino Flux: The neutrinos observed from Galactic contributions account for an estimated 6–13% of the all-sky astrophysical diffuse flux, which aligns well with extragalactic contributions previously identified by IceCube.
• Prospect for Further Exploration: These findings open up prospects for future research aimed at isolating and potentially resolving individual high-energy neutrino sources within the Milky Way. Advanced detection systems or supplementary observations from other astrophysical messengers could strengthen the source identification.

Conclusion

The paper demonstrates a significant advance in high-energy neutrino astronomy, pinpointing the Galactic plane as a source of cosmic neutrinos. It highlights the valuable contributions of statistical models and machine learning to data analysis, enabling researchers to probe the electromagnetic spectrum for potential cosmic ray sources. Moving forward, these findings could guide the design of more enhanced detection infrastructure and reinforce our comprehension of high-energy processes in the cosmos. The IceCube Neutrino Observatory continues to be at the forefront of astrophysical neutrino research, providing critical insights into the high-energy universe.