A Radio-quiet AGN as a candidate counterpart to neutrino event IceCube-200615A

TL;DR

This study targets IceCube-200615A, a high-significance astrophysical neutrino detection, and conducts an extensive multiwavelength follow-up to locate its counterpart. Using Swift/XRT, NuSTAR, VLA, UVOT, Fermi-LAT, HAWC, and archival ROSAT/eRASS data, the authors construct quasi-simultaneous broadband SEDs and translate the high-energy photon flux into a neutrino expectation. A Bayesian framework over a large catalog of candidate sources identifies 1RXS J093117.6+033146 (Source A) as the most probable counterpart, with an approximate posterior probability of 87.5% and a Bayes factor exceeding 30, though the inferred neutrino counts remain well below unity (Nν,max ≈ 0.07–0.47 depending on the SED model and ν-slope). The results support the growing view that radio-quiet AGN can contribute to IceCube's neutrino flux and extend prior hints of a connection between such AGN and high-energy neutrinos. Overall, the work demonstrates the value of coordinated multiwavelength campaigns and rigorous Bayesian source association for pinpointing neutrino origins.

Abstract

Follow-up observations of neutrino events have been a promising method for identifying sources of very-high-energy cosmic rays. Neutrinos are unambiguous tracers of hadronic interactions and cosmic rays. On June 15, 2020, IceCube detected a neutrino event with an 82.8% probability of being astrophysical in origin. To identify the astrophysical source of the neutrino, we used X-ray tiling observations to identify potential counterpart sources. We performed additional multiwavelength follow-up with NuSTAR and the VLA in order to construct a broadband spectral energy distribution (SED) of the most likely counterpart. From the SED, we calculate an estimate for the neutrinos we expect to detect from the source. While the source does not have a high predicted neutrino flux, it is still a plausible neutrino emitter. It is important to note that the other bright X-ray candidate sources consistent with the neutrino event are also radio-quiet AGN. A statistical analysis shows that 1RXS J093117.6+033146 is the most likely counterpart (87.5%) if the neutrino is cosmic in origin and if it is among X-ray detectable sources. This results adds to previous results suggesting a connection between radio-quiet AGN and IceCube neutrino events.

Figures (8)

• Figure 1: Swift/XRT mosaic image with a 7-point tiling observation showing the detections of Sources A, B, C, and D.
• Figure 2: Swift/UVOT mosaic image with a 7-point tiling observation showing the detections of Sources A, B, C, and D.
• Figure 3: PanSTARRS image of Source B, 2MASX J09303302+0344432.
• Figure 4: VLA C-band image of 1RXS J093117.6+033146.
• Figure 5: Multiwavelength SED of 1RXS J093117.6+033146. Quasi-simultaneous data is shown in purple, while archival data is shown in black. Absorbed and reddened (raw) data are shown in gray. The energy band used for the integration of the energy flux is shown in gray at the bottom right side. Multiple possible parabola models are shown in three colours: dark green, green and cyan. Due to the lack of a $\gamma$-ray detection, it is unclear which model best describes the source. The bottom panel shows the residuals for the purple model ($\beta=0.15$). All three models fit the X-ray data equally well, with negligible differences.