Speaker
Description
Radio flares have been proposed as possible signatures of astrophysical neutrino production. In TXS 0506+056, the 2017 IceCube-170922A /$gamma$-ray flare was followed by a GHz radio maximum roughly 2–3 years later. We investigate whether this delayed radio flare can be explained by the same compact region that produced the neutrinos and $gamma$-rays, as it expands downstream and becomes less affected by synchrotron self-absorption. Using LeHaMoC code in a fully time-dependent framework, we model the evolution of the emitting region starting from the 2017 flare parameters and compare the predicted 1.2–22 GHz light curves with RATAN-600 data. We study different scenarios with increasing levels of sophistication, including continuous injection and energy re-dissipation to particles on parsec scales. We find that a simple expanding-blob model cannot reproduce the observed radio behavior. Instead, the data are better explained by a downstream re-dissipation episode in the optically thin regime, followed by jet deceleration. In our one-zone framework, the delayed radio flare is therefore unlikely to result from a neutrino-production region that becomes radio-transparent. Rather, it appears to reflect downstream dissipation and changes in relativistic beaming. Because the radio flare is powered mainly by leptonic synchrotron emission and is largely insensitive to the proton population, it should not be regarded as a direct tracer of neutrino production.
