Abstract Neutrino astronomy saw its birth with the discovery by IceCube of a difFuse flux at energies above 60 TeV with intensity comparable to a predicted upper limit to the flux from extra-galactic sources of ultra-high energy cosmic rays (UHECRs). While such an upper limit corresponds to the case of calorimetric sources, in which cosmic rays lose all their energy into photo-pion production, the first statistically significant coincident observation between neutrinos and gamma-rays was observed from a blazar of intriguing nature. A very-high-energy muon event, of most probable neutrino energy of 290 TeV for an E −2.13 spectrum, alerted other observatories triggering a large amount of investigations in many bands of the electromagnetic (EM) spectrum. A high gamma-ray state from the blazar was revealed soon after the event and in a follow up to about 40 days. A posteriori observations also in the optical and in the radio indicated a rise of the flux from the TXS 0506+056 blazar. A previous excess of events of duration of more than 100 d was observed by IceCube with higher significance than the alert itself. These observations triggered more complex modelling than simple one zone proton synchrotron models for proton acceleration in jets of active galactic nuclei (AGNs) and more observations across the EM spectrum. A second evidence was a steady excess of about 50 neutrino events with reconstructed soft spectrum in a sample of lower energy well reconstructed muon events than the alert event. A hot spot was identified in a catalogue of 110 gamma-ray intense emitters and starburst galaxies in a direction compatible to NGC 1068 with significance of 2.9 σ . NGC 1068 hosts a mildly relativistic jet in a starburst galaxy, seen not from the jet direction but rather through the torus. This Seyfert II galaxy is at only 14.4 Mpc from the Earth. The source turned out to be also the hottest spot of an all-sky search. Analysed cumulatively, the catalogue excess was 3.3 σ with the contribution of NGC 1068 and TXS 0506+056, as expected, and other 2 sources, PKS 1424+240, and GB6 J1542+6129, with similar features to TXS 0506+056, indicating that they might all be Flat Spectrum Radio Quasars (FSRQs). While all these observations and the directions of the measured events contributing to diffuse fluxes hint to their extra-galactic origin, a few percent level contribution might be the end of a lower energy ‘granted’ flux of neutrinos from interactions of cosmic rays in the Galactic Plane. This relevant observation is at the reach of IceCube and other neutrino telescopes. These aspects were discussed at the conference and are summarised in this write up.
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Multimessenger observations of counterparts to IceCube-190331A
Abstract High-energy neutrinos are a promising tool for identifying astrophysical sources of high and ultra-high energy cosmic rays (UHECR). Prospects of detecting neutrinos at high energies (≳TeV) from blazars have been boosted after the recent association of IceCube-170922A and TXS 0506+056. We investigate the high-energy neutrino, IceCube-190331A, a high-energy starting event (HESE) with a high likelihood of being astrophysical in origin. We initiated a Swift/XRT and UVOT tiling mosaic of the neutrino localisation, and followed up with ATCA radio observations, compiling a multiwavelength SED for the most likely source of origin. NuSTAR observations of the neutrino location and a nearby X-ray source were also performed. We find two promising counterpart in the 90% confidence localisation region and identify the brightest as the most likely counterpart. However, no Fermi/LAT γ-ray source and no prompt Swift/BAT source is consistent with the neutrino event. At this point it is unclear whether any of the counterparts produced IceCube-190331A. We note that the Helix Nebula is also consistent with the position of the neutrino event, and we calculate that associated particle acceleration processes cannot produce the required energies to generate a high-energy HESE neutrino.
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- Award ID(s):
- 1914579
- NSF-PAR ID:
- 10178791
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- ISSN:
- 0035-8711
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/staa2148
