Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf

TL;DR

This paper reports the discovery of periodic, highly polarized radio bursts from an ultracool dwarf, demonstrating it as a prototype for a new class of transient radio sources driven by magnetic activity.

Contribution

The study provides the first detection of periodic coherent radio bursts from an ultracool dwarf, linking them to magnetic polar regions and electron cyclotron maser emission.

Findings

Periodic radio bursts with a 1.96-hour cycle were observed.

The bursts are 100% circularly polarized and broadband.

The emission mechanism is consistent with electron cyclotron maser instability.

Abstract

We report the detection of periodic (p = 1.96 hours) bursts of extremely bright, 100% circularly polarized, coherent radio emission from the M9 dwarf TVLM 513-46546. Simultaneous photometric monitoring observations have established this periodicity to be the rotation period of the dwarf. These bursts, which were not present in previous observations of this target, confirm that ultracool dwarfs can generate persistent levels of broadband, coherent radio emission, associated with the presence of kG magnetic fields in a large-scale, stable configuration. Compact sources located at the magnetic polar regions produce highly beamed emission generated by the electron cyclotron maser instability, the same mechanism known to generate planetary coherent radio emission in our solar system. The narrow beams of radiation pass our line of sight as the dwarf rotates, producing the associated periodic bursts. The resulting radio light curves are analogous to the periodic light curves associated with pulsar radio emission highlighting TVLM 513-46546 as the prototype of a new class of transient radio source.