Speaker
Description
The flat-spectrum radio quasar PKS~0215+015 ($z \simeq 1.715$) was found to be positionally and temporally coincident with the IceCube neutrino event IceCube-220225A, detected on 25~February~2022 with a reconstructed energy of $\sim$154~TeV. The source was the only $\gamma$-ray emitter within the 90\% neutrino localisation region and was independently confirmed to be in an elevated $\gamma$-ray state at the time of the alert, accompanied by a historic radio outburst and VLBI evidence for a new superluminal jet component. We present a multiwavelength analysis of PKS~0215+015 using \textit{Fermi}-LAT, \textit{Swift}-XRT and \textit{Swift}-UVOT data spanning nearly two decades, and construct the broadband spectral energy distribution (SED) for the flaring epoch coincident with the neutrino detection. The SED is well reproduced by a leptonic model (synchrotron, synchrotron self-Compton and external Compton emission), close to equipartition between the electron and magnetic field energy densities. A co-accelerated hadronic component, explored to assess the maximum neutrino flux allowed by the data, remains radiatively subdominant despite requiring a proton kinetic luminosity roughly two orders of magnitude above equipartition, illustrating the baryon-loading problem common to leptohadronic neutrino-blazar modelling. An independent size estimate from short-term $\gamma$-ray variability agrees closely with the SED-derived emission-region size. We discuss the implications of these results for the plausibility of a physical association between PKS~0215+015 and IceCube-220225A, and for future multimessenger searches involving high-redshift FSRQs.