2013MNRAS.434.3078K

Gamma-ray observations of a stellar tidal disruption event (TDE) detected by the Swift satellite and follow-up observations in radio, millimetre (mm), infrared and X-ray bands have provided a rich data set to study accretion on to massive black holes, production of relativistic jets and their interaction with the surrounding medium. The radio and X-ray data for TDE Swift J1644+57 provide a conflicting picture regarding the energy in relativistic jet produced in this event: X-ray data suggest jet energy declining with time as t-5/3 whereas the nearly flat light curves in radio and mm bands lasting for about 100d have been interpreted as evidence for the total energy output increasing with time. We show in this work that flat light curves do not require addition of energy to decelerating external shock (which produced radio and mm emission via synchrotron process), instead the flat behaviour is due to inverse-Compton cooling of electrons by X-ray photons streaming through the external shock; the higher X-ray flux at earlier times cools electrons more efficiently thereby reducing the emergent synchrotron flux, and this effect weakens as the X-ray flux declines with time.