The IceCube Neutrino Observatory, a cubic-kilometer-sized telescope at the South Pole, has been issuing real-time alerts to the public within minutes of the detection of astrophysical, ghostlike particles called neutrinos. However, the sources of the astrophysical neutrinos detected by IceCube remain largely unknown.
One class of objects that are probable sources of astrophysical neutrinos are active galactic nuclei (AGN), supermassive black holes at the center of a galaxy. IceCube recently found evidence of high-energy neutrino emission from the AGN known as NGC 1068. Previously, the first evidence of an astrophysical source came from the coincident detection of a high-energy neutrino, selected by the real-time alert program, with the blazar TXS 0506+056.
In a new study submitted to The Astrophysical Journal, the IceCube Collaboration presents a new method that correlates likely astrophysical neutrinos, or “alert events,” with catalogs of candidate sources. No significant neutrino emission was found from the sources considered in those catalogs.
For the method, three correlation analyses used neutrino “track” alerts from the recently published event catalog called ICECAT-1, blazars from the Fermi Large Area Telescope (Fermi-LAT) 4LAC-DR2 catalog, and AGNs from the Radio Fundamental Catalog (RFC). The analyses looked at 1) bright gamma-ray blazars, 2) blazars that were particularly bright in gamma rays at the neutrino arrival time, and 3) radio-bright (intense in radio wavelengths) AGNs.
“The first step in the analysis method is to calculate the contribution of each individual neutrino with a coincident source, which includes the information from the angular reconstruction method, the probability of the neutrino to be astrophysical, and how bright the source is,” explains Cristina Lagunas Gualda, a physics PhD student at Deutsches Elektronen-Synchrotron and study lead. “Then all the contributions of the neutrinos are combined and compared to what one would obtain if all the coincidences happened by chance.”
From the three analyses performed, no significant neutrino emission was detected from the sources in the catalogs. Although the results imply that the majority of neutrinos from these alerts are neither produced in bright or flaring gamma-ray blazars nor in radio-bright AGNs, individual neutrinos from the alerts could still be produced in some of these sources.
“The new statistical method is a framework that permits testing of other production mechanisms for high-energy neutrino events,” says Lagunas Gualda. “It uses all the information from the angular reconstruction method that wasn’t publicly available before the ICECAT-1 data release.”
+ info “Search for correlations of high-energy neutrinos detected in IceCube with radio-bright AGN and gamma-ray emission from blazars,” IceCube Collaboration: R. Abbasi et al. Submitted to The Astrophysical Journal, arxiv.org/abs/2304.12675