Published on Mon Sep 06 2021

What powers the radio emission in TDE AT2019dsg: a long-lived jet or the disruption itself?

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The tidal disruption event, AT2019dsg, was observed across a broad range of electromagnetic-wavelengths from radio to X-rays, and it was possibly accompanied by a high-energy neutrino. We study the nature of the radio-emitting outflow by analyzing the synchrotron self-absorbed spectra in terms of the equipartition model. We find that the time evolution of the outflow radius can be interpreted as either free expansion or deceleration. If the former, the outflow was launched 40 days before the optical peak; if the latter, the launch was 10 days after the optical peak. In addition, the energy in the radio-emitting region increases over time. This second conclusion is most naturally interpreted by a scenario resembling the earliest stage of a supernova remnant: as more and more material is swept up, it is heated by the forward shock at the expense of the outflow's kinetic energy. Energy injection from an accreting BH cannot be completely excluded, but the injection rate is very different from the fallback luminosity, requiring further physical explanation. If the neutrino association is real, the scale of energy injection needed is much greater than for the radio emission, suggesting that the detected neutrino did not arise from the radio emitting region.