Blazar-IceCube neutrino association revisited

The reported association of high-energy neutrino event IceCube-170922A and blazar TXS $0506+056$ has sparked discussion about blazars as sources of cosmic neutrinos. In this paper, we use publicly released IceCube data and blazar locations from Roma-BzCat to test spatial correlation between neutrino events and blazar locations. We also scrutinize the correlation between the $\gamma$-ray flux and neutrino flux of blazars by applying a temporal filter onto the data based on the Fermi monitored source list. We find no compelling evidence to prove blazars as the main source of cosmic neutrinos, as known before the detected IceCube-170922A/TXS $0506+056$ association. While we do not rule out the association between IceCube-170922A and TXS $0506+056$, the significance level we obtained is not high enough to claim a strong association. If such an association is real, a special physical condition is desired to allow a small fraction of blazars to become bright neutrino sources.

Figure 1

The distribution of the simulated number of matches between the directions of blazars in ROMA-BzCat and the directions of IceCube neutrino alert events. The vertical line denotes the observed value of 16.

Figure 2

The distribution of the smallest distances between blazars and neutrino events in each simulation. The vertical line denotes the observed value of 0.0763°.

Figure 3

The distribution of the association TS for blazars.

Figure 4

The distribution of the number of matches between all blazars and neutrino events with energies greater than 100 TeV. The vertical line denotes the number of blazar matches with TXS $0506+056$, 40.

Figure 5

Distributions of $n_s$ and TS from Monte Carlo simulations for 3C 279. The vertical lines show the observed values of 0.439 and 0.067.