Multi-messenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A (1807.08816v1)

Abstract: Individual astrophysical sources previously detected in neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017 we detected a high-energy neutrino, IceCube-170922A, with an energy of approximately 290 TeV. Its arrival direction was consistent with the location of a known gamma-ray blazar TXS 0506+056, observed to be in a flaring state. An extensive multi-wavelength campaign followed, ranging from radio frequencies to gamma-rays. These observations characterize the variability and energetics of the blazar and include the first detection of TXS 0506+056 in very-high-energy gamma-rays. This observation of a neutrino in spatial coincidence with a gamma-ray emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

• The paper demonstrates a statistically significant (3σ) spatial and temporal association between TXS 0506+056 and IceCube-170922A.
• The paper employs multi-wavelength data from Fermi-LAT and MAGIC to correlate gamma-ray flaring with the detected neutrino event.
• The paper suggests that proton acceleration in blazar jets produces pions that decay into neutrinos and gamma-rays, indicating a plausible source of cosmic rays.

Multi-messenger Observations of a Flaring Blazar Coincident with High-energy Neutrino IceCube-170922A

The detection of high-energy neutrinos offers a profound avenue into the paper of astrophysical sources, arguably providing unique insights beyond what is possible through electromagnetic observations alone. The paper under discussion presents a comprehensive analysis of multi-messenger observations associated with the high-energy neutrino event IceCube-170922A, detected on September 22, 2017. This neutrino event is noted for its spatial and temporal association with a flaring blazar known as TXS 0506+056. This finding has significant implications for identifying potential astrophysical sources of cosmic neutrinos, particularly in blazars.

Key Observations and Analysis

1. Neutrino Detection: IceCube-170922A was identified as a high-energy neutrino event by the IceCube Neutrino Observatory, characterized by an energy deposition of approximately 23.7 TeV within the detector and an estimated true neutrino energy of approximately 290 TeV. The spatial coincidence with the flaring state of TXS 0506+056, located within 0.1 degrees of the reconstructed neutrino trajectory, presents a statistically compelling case against chance coincidence, disfavored at a significance level of 3σ.
2. Multi-wavelength Observations: Following the neutrino alert, a battery of instruments across the electromagnetic spectrum pursued the blazar. Observations from the Fermi Large Area Telescope (LAT), MAGIC, and other telescopes confirmed heightened activity in energies ranging from radio to VHE gamma-rays. Specifically, MAGIC confirmed very-high-energy (VHE) gamma-ray emission from the blazar, marking a critical complementary insight to neutrino astrophysics.
3. Detection of Gamma-rays: Fermi-LAT reported an enhanced gamma-ray state extending over several months, which correlates well with the neutrino detection. The VHE gamma-ray flux detected by MAGIC further reinforces the hypothesis that TXS 0506+056 could be a source of cosmic high-energy neutrinos.
4. Physical Interpretation: The association between IceCube-170922A and TXS 0506+056 suggests that certain blazars could be efficient accelerators of protons or heavier nuclei to energies sufficient for pion production. Subsequently, these pions decay to produce the observed neutrinos and gamma-rays. This observation provides evidence supporting the hypothesis that blazars may contribute to the sources of ultra-high-energy cosmic rays.

Implications and Speculation

The paper presents a critical milestone in the multi-messenger astrophysics approach, providing a template for subsequent analyses of neutrinos from astrophysical sources concurrent with electromagnetic signals. The evidence suggests that blazars, notably those in flaring states, are likely sources of high-energy neutrinos, thus contributing to our understanding of cosmic ray origins.

The paper opens up numerous avenues for future research. These include further characterization of the mechanisms at play within blazar jets that facilitate neutrino production, and the exploration of additional blazar-neutrino associations to refine our understanding of the population contributing to the diffuse neutrino flux. It also highlights the necessity for coordinated real-time alerts across observatories, enabling rapid multi-messenger follow-ups that can capture transient astrophysical phenomena.

In summary, the work illustrates how neutrino observations, when coupled with electromagnetic data, not only spotlight potential origins of high-energy cosmic rays but also enrich our understanding of extreme astrophysical processes. This realization affirms the critical role of multi-messenger astronomy in elucidating the high-energy universe.