Abstract
ABSTRACT High-energy neutrinos are a promising tool for identifying astrophysical sources of high and ultra-high energy cosmic rays (UHECRs). 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 localization and followed up with ATCA radio observations, compiling a multiwavelength spectral energy distribution (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 per cent confidence localization 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.
Highlights
Cosmic rays arriving at the Earth have been detected up to the extreme energies of 1021 eV since more than a century ago – yet their origin remains elusive (e.g. Norman, Melrose & Achterberg 1995)
The flare contribution may be subdominant while the core contribution can be dominant in the bulk flux (Murase et al 2019). This would change the current picture that particle acceleration in AGN jets is the dominant way to produce neutrinos from AGN (Kadler et al 2016; IceCube Collaboration et al 2018) and potentially counter indicated by the high observed energy of this neutrino event
We find four X-ray sources in the tiled Swift/XRT mosaic observations with two having high detection significance, while no new sources or activity in a known one were identified in the NuSTAR observations
Summary
Cosmic rays arriving at the Earth have been detected up to the extreme energies of 1021 eV since more than a century ago – yet their origin remains elusive (e.g. Norman, Melrose & Achterberg 1995). A promising tool for identifying the astrophysical sources of high and ultra-high energy cosmic rays are high-energy neutrinos as they are not deflected in interstellar and intergalactic magnetic fields Consistent with these expectations, a diffuse extraterrestrial flux of high-energy neutrinos has been observed by the IceCube neutrino observatory over more than a decade of observation (Aartsen et al 2013; IceCube Collaboration 2014; Haack & Wiebusch 2017). On 2019 March 31, the IceCube Neutrino Observatory identified a high-energy neutrino candidate (labelled IceCube-190331A), likely produced by a muon neutrino This event was publicly distributed through the gamma-ray coordinates network (GCN; Barthelmy et al 1995) within 34 s (GCN/AMON NOTICE IceCube-190331A 2017).
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