Since 2016, the IceCube Neutrino Observatory—a detector buried in a cubic kilometer of Antarctic ice—has been issuing real-time alerts sent to the public within minutes of the detection of astrophysical, ghostlike particles called neutrinos. IceCube’s prompt observations are key in the emerging field of multimessenger astronomy where the combined measurements across the electromagnetic spectrum are used to probe the nature of astrophysical phenomena.
Real-time alerts are followed up by different ground- and space-based telescopes that can point in the direction of the neutrino in the sky in order to identify a probable transient source of the neutrino. One such coincident detection of neutrinos and gamma rays led to the breakthrough discovery of the blazar TXS 0506+056 as a potential astrophysical source of neutrinos in 2018. Now, IceCube has produced a catalog of real-time neutrino events that will help with future multiwavelength follow-up observations.
In a new report submitted to The Astrophysical Journal Supplement, the IceCube Collaboration presents the first IceCube Event Catalog of Alert Tracks (ICECAT-1), consisting of 275 neutrino events of likely astrophysical origin from 2011 to 2020.
In 2019, several improvements were introduced to the real-time alert program, including increased signal purity and an expanded alert selection. Namely, two new alert categories for signal purity were introduced, called “gold” and “bronze” alerts, for neutrino events that leave a “track” signature in the detector. The gold events are, on average, more likely to be astrophysical in origin than bronze events. The new event selection thereby increased the total number of real-time alerts sent per year while also reducing the number of events with poor reconstruction.
“To compile this catalog, we applied the same stringent criteria that we have been applying in real time since 2019 to all our archival data going back to 2011,” says Mehr Un Nisa, a postdoctoral researcher at Michigan State University. “We then obtained the directions and energies of these events based on our best current understanding of the detector.”
ICECAT-1 is also accompanied by an online database of all alert events, allowing the community to access key quantities for each alert and visualize its most likely position in the sky. Both ICECAT-1 and the database are now publicly available and will be updated periodically in the future.
“The sources of the astrophysical neutrinos observed by IceCube is still an open question,” says Erik Blaufuss, a research scientist at the University of Maryland. “By sharing these alerts with the community, both for our historical catalog and future alerts, we can search for correlations in signals across multiple wavelengths and messengers.”
+ info “IceCat-1: the IceCube Event Catalog of Alert Tracks,” IceCube Collaboration: R. Abbasi et al. Submitted to The Astrophysical Journal Supplement, arxiv.org/abs/2304.01174