- Collaboration, FL
- Collaboration, AS
- Collaboration, I
- Garrappa, S
- Buson, S
- Franckowiak, A
- Shappee, BJ
- Beacom, JF
- Dong, S
- Holoien, TWS
- Kochanek, CS
- Prieto, JL
- Stanek, KZ
- Thompson, TA
- Aartsen, MG
- Ackermann, M
- Adams, J
- Aguilar, JA
- Ahlers, M
- Ahrens, M
- Alispach, C
- Andeen, K
- Anderson, T
- Ansseau, I
- Anton, G
- Argüelles, C
- Auffenberg, J
- Axani, S
- Backes, P
- Bagherpour, H
- Bai, X
- Barbano, A
- Barwick, SW
- Baum, V
- Bay, R
- Beatty, JJ
- Becker, KH
- Tjus, JB
- Benzvi, S
- Berley, D
- Bernardini, E
- Besson, DZ
- Binder, G
- Bindig, D
- Blaufuss, E
- Blot, S
- Bohm, C
- Börner, M
- Böser, S
- Botner, O
- Bourbeau, E
- Bourbeau, J
- Bradascio, F
- Braun, J
- Bretz, HP
- Bron, S
- Brostean-Kaiser, J
- Burgman, A
- Busse, RS
- Carver, T
- Chen, C
- Cheung, E
- Chirkin, D
- Clark, K
- Classen, L
- Collin, GH
- Conrad, JM
- Coppin, P
- Correa, P
- Cowen, DF
- Cross, R
- Dave, P
- De André, JPAM
- Clercq, CD
- Delaunay, JJ
- Dembinski, H
- Deoskar, K
- Ridder, SD
- Desiati, P
- Vries, KDD
- Wasseige, GD
- With, MD
- Deyoung, T
- Diaz, A
- Díaz-Vélez, JC
- Dujmovic, H
- Dunkman, M
- Dvorak, E
- Eberhardt, B
- Ehrhardt, T
- Eller, P
- Evenson, PA
- Fahey, S
- Fazely, AR
- Felde, J
- Filimonov, K
- Finley, C
- Friedman, E
- Fritz, A
- et al.
After the identification of the gamma-ray blazar TXS 0506+056 as the first compelling IceCube neutrino source candidate, we perform a systematic analysis of all high-energy neutrino events satisfying the IceCube realtime trigger criteria. We find one additional known gamma-ray source, the blazar GB6 J1040+0617, in spatial coincidence with a neutrino in this sample. The chance probability of this coincidence is 30% after trial correction. For the first time, we present a systematic study of the gamma-ray flux, spectral and optical variability, and multiwavelength behavior of GB6 J1040+0617 and compare it to TXS 0506+056. We find that TXS 0506+056 shows strong flux variability in the Fermi-Large Area Telescope gamma-ray band, being in an active state around the arrival of IceCube-170922A, but in a low state during the archival IceCube neutrino flare in 2014/15. In both cases the spectral shape is statistically compatible (≤2σ) with the average spectrum showing no indication of a significant relative increase of a high-energy component. While the association of GB6 J1040+0617 with the neutrino is consistent with background expectations, the source appears to be a plausible neutrino source candidate based on its energetics and multiwavelength features, namely a bright optical flare and modestly increased gamma-ray activity. Finding one or two neutrinos originating from gamma-ray blazars in the given sample of high-energy neutrinos is consistent with previously derived limits of neutrino emission from gamma-ray blazars, indicating the sources of the majority of cosmic high-energy neutrinos remain unknown.