Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A

Abstract

Previous detections of individual astrophysical sources of 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 ~290 tera-electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray-emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

The Blazar TXS 0506+056 Associated with a High-energy Neutrino: Insights into Extragalactic Jets and Cosmic-Ray Acceleration

“…On the other hand, the data from Fermi reveals enhanced gamma-ray activity of TXS0506+056 lasting several months. We consider physical models of the source that are compatible with the detection of one neutrino by IceCube during 0.5 years in the energy range reported in Aartsen et al (2018). By invoking a dense field of low-energy photons originating outside of the jet as targets for photohadronic interactions, the measured neutrino event can be interpreted consistently with the EM observations.…”

“…lower and upper limits being 183 TeV (200 TeV) and 4.3 PeV (7.5 PeV), respectively, assuming a spectral index of −2.13 (−2.0) for the diffuse astrophysical muon neutrino spectrum (Aartsen et al 2014). No additional excess of neutrinos with lower energy was found from the direction of TXS0506+056 near the time of the alert (Aartsen et al 2018).…”

“…In the VHE band, TXS 0506+056 was followed up by several Imaging Atmospheric Cherenkov Telescopes (IACTs), with the earliest one starting a few hours after the neutrino alert (Aartsen et al 2018). (Aleksić et al 2016) is a system of two 17 m ground-based IACTs, operating in stereoscopic mode since fall 2009 at the Roque de los Muchachos Observatory (28°.8 N, 17°.8 W, 2200 m a.s.l.…”

“…The probability of a high-energy neutrino being detected by chance coincidence with a flaring blazar from Fermi-LAT catalogs was found to be disfavored at a 3σ confidence level, mostly due to the precise determination of the direction of IceCube-170922A (Aartsen et al 2018).…”

“…29 Hereafter, we interpret within a coherent scenario the available multi-messenger data presented in Aartsen et al (2018), together with additional MAGIC data for TXS 0506 +056, under the assumption that the association of IceCube-170922A and the blazar in an active state is genuine, and that 28 The IceCube Collaboration, GRB Coordinates Network, Circular Service, No. 21916 (2017).…”