Federica Bradascio, "Search for cross-correlations between IceCube neutrinos and AGN cores selected in various bands of the electromagnetic spectrum"

Friday 10 Dec 2021, 10:30 → 11:30 Europe/Berlin

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IceCube is a cubic-kilometer Cherenkov telescope operating at the South Pole. In 2013, it discovered a diffuse flux of high-energy astrophysical neutrinos and has more recently found compelling evidence for a flaring blazar being a source of high-energy neutrinos. However, the sources responsible for the emission of the majority of the detected neutrinos are still unknown. Besides the construction of larger detectors and the accumulation of additional data, it is important to refine the existing point spread function of IceCube and to study more classes of objects that could be responsible for neutrino production. In the first part of this talk, I will address the first issue by presenting a new muon reconstruction which improves the muon angular resolution of IceCube of about 20%. In the second part, I will present the results of an analysis exploring the possibility that the neutrino flux observed by IceCube is produced in the cores of Active Galactic Nuclei (AGN). Various models have predicted neutrino emission from the accretion disks of AGN. In this case, the neutrino luminosity would not depend strongly on the properties of the relativistic jet. Both jetted and non-jetted AGN could contribute to the neutrino flux. A stacking analysis is conducted to test for a correlation between various sub-populations of AGN and high-energy neutrinos using eight years of IceCube data. AGN are selected based on their radio emission, infrared color properties, and X-ray flux using the NVSS, AllWISE, ROSAT and XMMSL2 catalogs. The accretion disk luminosity estimated by the observed soft X-ray flux is used as a proxy for the contribution of selected galaxies to the neutrino signal. For the largest sample  in this search – IR color selected AGN – consisting of 32249 sources, the best fit finds an excess of 105 +/-44 neutrinos over expectations from the background of atmospheric and astrophysical neutrinos, corresponding to a post-trial significance of 2.6σ. Interpreted as a genuine signal and assuming proportionality of X-ray and neutrino fluxes, this observation implies that at 100 TeV ~54% of the observed neutrinos arise from particle acceleration in the core of AGN.