A high-energy neutrino event detected by IceCube on 22 September 2017 was coincident in direction and time with a gamma-ray flare from the blazar TXS 0506+056. Prompted by this association, we investigated 9.5 years of IceCube neutrino observations to search for excess emission at the position of the blazar. We found an excess of high-energy neutrino events, with respect to atmospheric backgrounds, at that position between September 2014 and March 2015. Allowing for time-variable flux, this constitutes 3.5σ evidence for neutrino emission from the direction of TXS 0506+056, independent of and prior to the 2017 flaring episode. This suggests that blazars are identifiable sources of the high-energy astrophysical neutrino flux.

We present the dissection in space, time, and energy of the region around the IceCube-170922A neutrino alert. This study is motivated by: (1) the first association between a neutrino alert and a blazar in a flaring state, TXS 0506+056; (2) the evidence of a neutrino flaring activity during 2014 -2015 from the same direction; (3) the lack of an accompanying simultaneous γ-ray enhancement from the same counterpart; (4) the contrasting flaring activity of a neighbouring bright γ-ray source, the blazar PKS 0502+049, during 2014 -2015. Our study makes use of multi-wavelength archival data accessed through Open Universe tools and includes a new analysis of Fermi-LAT data. We find that PKS 0502+049 contaminates the γ-ray emission region at low energies but TXS 0506+056 dominates the sky above a few GeV. TXS 0506+056, which is a very strong (top percent) radio and γ-ray source, is in a high γ-ray state during the neutrino alert but in a low though hard γ-ray state in coincidence with the neutrino flare. Both states can be reconciled with the energy associated with the neutrino emission and, in particular during the low/hard state, there is evidence that TXS 0506+056 has undergone a hadronic flare with very important implications for blazar modelling. All multi-messenger diagnostics reported here support a single coherent picture in which TXS 0506+056, a very high energy γ-ray blazar, is the only counterpart of all the neutrino emissions in the region and therefore the most plausible first non-stellar neutrino and, hence, cosmic ray source.

We propose that the inner engine of a type I binary-driven hypernova (BdHN) is composed of a Kerr black hole (BH) in a non-stationary state, embedded in a uniform magnetic field B 0 aligned with the BH rotation axis, and surrounded by an ionized plasma of extremely low density of 10 −14 g cm −3 . Using GRB 130427A as a prototype we show that this inner engine acts in a sequence of elementary impulses. Electrons are accelerated to ultra-relativistic energy near the BH horizon and, propagating along the polar axis, θ = 0, they can reach energies of ∼ 10 18 eV, and partially contribute to ultra-high energy cosmic rays (UHECRs). When propagating with θ = 0 through the magnetic field B 0 they give origin by synchrotron emission to GeV and TeV radiation. The mass of BH, M = 2.3M , its spin, α = 0.47, and the value of magnetic field B 0 = 3.48 × 10 10 G, are determined self-consistently in order to fulfill the energetic and the transparency requirement. The repetition time of each elementary impulse of energy E ∼ 10 37 erg, is ∼ 10 −14 s at the beginning of the process, then slowly increasing with time evolution. In principle, this "inner engine" can operate in a GRB for thousands of years. By scaling the BH mass and the magnetic field the same "inner engine" can describe active galactic nuclei (AGN).

We report on an analysis of Fermi Large Area Telescope data from four years of observations of the nearby radio galaxy Centaurus A (Cen A). The increased photon statistics results in a detection of high-energy (>100 MeV) gamma-rays up to 50 GeV from the core of Cen A, with a detection significance of about 44σ . The average gamma-ray spectrum of the core reveals evidence for a possible deviation from a simple power law. A likelihood analysis with a broken power-law model shows that the photon index becomes harder above E b 4 GeV, changing from Γ 1 = 2.74 ± 0.03 below to Γ 2 = 2.09 ± 0.20 above. This hardening could be caused by the contribution of an additional high-energy component beyond the common synchrotron self-Compton jet emission. No clear evidence for variability in the high-energy domain is seen. We compare our results with the spectrum reported by H.E.S.S. in the TeV energy range and discuss possible origins of the hardening observed.