Mrk 421: Upper limits from a neutrino search with IceCube
ATel #17622; Anna Franckowiak (Ruhr-University Bochum), Alicia Mand (University of Wisconsin-Madison), Marcos Santander (University of Alabama), Ignacio Taboada (Georgia Tech), Jessie Thwaites (Queen's University), Angela Zegarelli (Ruhr-University Bochum)
on 21 Jan 2026; 21:26 UT
Credential Certification: Anna Franckowiak (anna.franckowiak@desy.de)
Subjects: Neutrinos, Blazar
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
IceCube has performed a search for track-like muon neutrino events arriving from the direction of blazar Mrk421 following reports from LHAASO (ATel #17535), VERITAS (ATel #17594), SVOM (ATel #17595), SST-1M (ATel #17597), and ASTRI-1 (ATel #17602) in a time range of two weeks to cover the reported emission phases in X-rays and gamma-rays (2026-01-02 00:00:00.00 UTC to 2026-01-16 00:00:00.00 UTC), during which IceCube was collecting good quality data.
For this search, we report a p-value of 1.0 with respect to an atmospheric background-only hypothesis. We accordingly derive a time-integrated muon-neutrino flux upper limit for this source of E^2 dN/dE = 6.7e-2 GeV cm^-2 at 90% CL, under the assumption of an E^-2 power law. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum are between approximately 700 GeV and 400 TeV.
The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu.
[1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021)
