Radio transients from stellar tidal disruption by massive black holes

TL;DR

This paper predicts that stellar tidal disruptions by black holes can produce bright, long-lasting radio transients due to relativistic jets interacting with the interstellar medium, which can be detected by upcoming radio surveys.

Contribution

It introduces the idea that relativistic jets from tidal disruption events produce observable radio transients, providing a new method to detect and study these phenomena.

Findings

Relativistic jets decelerate via interaction with interstellar medium.

Synchrotron radiation produces bright radio-infrared transients peaking around 1 year.

Upcoming radio surveys could discover tens to hundreds of tidal disruptions annually.

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, UV and X-ray wavelengths. Here we explore the observational consequences if a modest fraction of the accretion power is channeled into an ultra-relativistic outflow. We show that a relativistic jet decelerates due to its interaction with the interstellar medium at sub-parsec distances from the black hole. Synchrotron radiation from electrons accelerated by the reverse shock powers a bright radio-infrared transient that peaks on a timescale ~1 yr 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, in which the flow parameters are independently constrained.