Dissecting the broadband emission from γ-ray blazar PKS 0735+178 in search of neutrinos

Raj Prince, Saikat Das, Nayantara Gupta, Pratik Majumdar, Bożena Czerny

Published 2023-01-16Version 1

The origin of the diffuse flux of TeV-PeV astrophysical neutrinos is still unknown. The $\gamma$-ray blazar PKS 0735+178, located within a 90% error region expanded by a factor of 1.3 of the neutrino event IC-211208A, was found to be flaring in multi-frequency wavebands at the time of detection by IceCube Observatory. In addition to leptonic synchrotron (SYN) and synchrotron self-Compton (SSC) emission, we invoke photohadronic (p$\gamma$) interactions inside the jet to model the spectral energy distribution (SED) and neutrino emission. We analyze the long-term $\gamma$-ray and X-ray data to generate the broadband SED. The temporal light curve indicates that the source was in a high state in optical UV, $\gamma$-ray, and X-ray range during the neutrino detection epoch. In the one-zone lepto-hadronic model, the SSC photons do not provide enough seed photons for p$\gamma$ interactions to explain the neutrino event. However, including an external photon field yields a neutrino event rate of 0.2 in 100 days, for the IceCube detector, for physically motivated values of the magnetic field, an external photon field peaking at optical wavelength, and other jet parameters without exceeding the Eddington luminosity. The radiation from secondary electrons at X-ray energies severely constrains the neutrino flux to a lower value than found in previous studies. In contrast, the pion decay cascade flux at GeV energies is subdominant at the high-energy peak of the SED, suggesting a higher correlation of neutrinos with X-ray emission is plausible.