Radio transients from stellar tidal disruption by massive black holes

Abstract

The tidal disruption of a star by a supermassive black hole provides us with a rare glimpse of these otherwise dormant beasts. It has long been predicted that the disruption will be accompanied by a thermal 'flare', powered by the accretion of bound stellar debris. Several candidate disruptions have been discovered in this manner at optical, ultraviolet and X-ray wavelengths. Here we explore the observational consequences if a modest fraction of the accretion power is channelled into an ultrarelativistic outflow. We show that a relativistic jet decelerates due to its interaction with the interstellar medium at subparsec distances from the black hole. Synchrotron radiation from electrons accelerated by the reverse shock powers a bright radio-infrared transient that peaks on a time-scale ~1yr after disruption. Emission from the forward shock may be detectable for several years after the peak. Deep radio follow-up observations of tidal disruption candidates at late times can test for the presence of relativistic ejecta. Upcoming radio transient surveys may independently discover tens to hundreds of tidal disruptions per year, complimenting searches at other wavelengths. Non-thermal emission from tidal disruption probes the physics of jet formation under relatively clean conditions. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.