[Paper Review] Astrophysics Uniquely Enabled by Observations of High-Energy Cosmic Neutrinos

M. Ackermann, M. Ahlers+17 more|Research at the University of Copenhagen (University of Copenhagen)|Mar 11, 2019

Astrophysics and Cosmic Phenomena35 references47 citations

TL;DR

The paper argues that high-energy neutrino astronomy uniquely probes the most energetic non-thermal sources, outlining science goals, observatory requirements, and the promise of multi-messenger campaigns to identify and characterize cosmic accelerators.

ABSTRACT

High-energy cosmic neutrinos carry unique information about the most energetic non-thermal sources in the Universe. This white paper describes the outstanding astrophysics questions that neutrino astronomy can address in the coming decade. A companion white paper discusses how the observation of cosmic neutrinos can address open questions in fundamental physics. Detailed measurements of the diffuse neutrino flux, measurements of neutrinos from point sources, and multi-messenger observations with neutrinos will enable the discovery and characterization of the most energetic sources in the Universe.

Motivation & Objective

• Motivate neutrino astronomy as a direct probe of the most energetic non-thermal sources in the Universe.
• Outline how detailed measurements of diffuse and point-source neutrino fluxes enable source discovery and environment characterization.
• Highlight the role of multi-messenger observations (photons, cosmic rays, gravitational waves) in identifying and understanding neutrino sources.
• Describe the observational requirements and a staged, multi-observatory approach to advance the science over the next decade.

Proposed method

• Advocate large detector arrays with low backgrounds to measure neutrino flux densities and spatial distributions.
• Emphasize sub-degree pointing resolution for source catalog correlations and flavor-specific measurements for per-flavor fluxes.
• Promote real-time alerts and multi-messenger coordination to enable neutrino-triggered follow-up observations.
• Recommend a staged, multi-observatory approach with complementary sky coverage and detection mechanisms to cross-check results.
• Use correlations between neutrinos, gamma rays, and cosmic rays to constrain source models and hadronic acceleration scenarios.

Experimental results

Research questions

• RQ1 What populations and environments are responsible for the diffuse high-energy neutrino flux observed by IceCube?
• RQ2 Can neutrino observations, especially in coincidence with gamma rays or gravitational waves, identify and characterize the sources of the most energetic cosmic accelerators?
• RQ3 How do neutrino flavor ratios and per-flavor fluxes inform neutrino production mechanisms at astrophysical sources?
• RQ4 What are the connections between the diffuse neutrino flux and transient sources such as GRBs, TDEs, and jet-powered supernovae?
• RQ5 What level of observational sensitivity and sky coverage is required to discover and resolve individual neutrino point sources?],
• RQ6 key_findingsOptionsLanguageThe=
• RQ7 key_findings_nonemptyContentCounter=3,

Key findings

• Astrophysical neutrinos have been observed in the 10 TeV to 10 PeV range, indicating a cosmic flux that requires further source identification.
• Coincident neutrino and gamma-ray observations from TXS 0506+056 provide evidence of an extragalactic neutrino source, but a sizable fraction of the diffuse flux remains unresolved from known blazars.
• There is a lack of established neutrino point sources after extensive observations, implying a population of weak extragalactic sources; multi-messenger campaigns and improved detectors are needed to reveal these sources.
• Precise measurements of the neutrino flux and flavor composition, combined with real-time multi-messenger alerts, will help localize and characterize the sources of high-energy neutrinos.
• Multi-messenger correlations between neutrinos, gamma rays, and cosmic rays can test unified models of cosmic particle production and constrain source environments.