The broad-band spectral energy distribution of candidate neutrino blazars

Abstract

Blazars, the jet-dominated class of active galactic nuclei comprising flat-spectrum radio quasars (FSRQs) and BL Lacertae objects (BL Lacs), are now increasingly identified as potential sources of high-energy neutrinos. Such neutrino blazars are ideal targets to investigate the high-energy emission processes and to understand their role as neutrino sources. We report results on four candidate neutrino blazars, PKS 0446+112, TXS 0506+056, PKS 1424−418, and PKS 1502+106. We carried out γ -ray spectral and timing analysis on three time periods that comprise a quiescent epoch, an epoch that corresponds to neutrino detection, and a flaring epoch. We also carried out modelling of the broad-band spectral energy distribution (SED) on those three epochs. We found that the γ -ray spectra of the BL Lac TXS 0506+056 can be adequately described by a power law, while the spectra of the other three FSRQs require a log-parabola model. On shorter time-scales, we observed flux variability with doubling/halving time-scales of 4.70, 9.24, 30.76, and 15.42 h for PKS 0446+112, TXS 0506+056, PKS 1424−418, and PKS 1502+106,respectively. The SEDs of most of the epochsforthe sources are well explained by a leptonic scenario. However, the quiescent epoch of PKS 1502+106 and the neutrino emission epoch of PKS 0446+112 required an additional hadronic component to reproduce the observed SEDs. Our analysis reveals a complex interplay of leptonic and hadronic processes. While certain neutrino-associated epochs align with a leptonic model, others necessitate a hadronic component to explain the emission features.