The 5 GHz Arecibo Search for Radio Flares from Ultracool Dwarfs

TL;DR

This study conducted a radio survey of brown dwarfs and an exoplanetary system at 4.75 GHz, detecting radio flares from the coolest brown dwarf yet, demonstrating radio detection as a tool for studying magnetic fields in substellar objects.

Contribution

First radio detection of a flare from a T6.5 brown dwarf, extending the known temperature range of radio-emitting brown dwarfs and exploring magnetic fields in the coolest substellar objects.

Findings

Detected radio flares from a T6.5 brown dwarf.

Extended the temperature range of radio-emitting brown dwarfs to ~900 K.

Tentative flare detection from an L1 dwarf.

Abstract

We present the results of a 4.75 GHz survey of 33 brown dwarfs and one young exoplanetary system for flaring radio emission, conducted with the 305-m Arecibo radio telescope. The goal of this program was to detect and characterize the magnetic fields of objects cooler than spectral type L3.5, the coolest brown dwarf detected prior to our survey. We have also attempted to detect flaring radio emission from the HR 8799 planetary system, guided by theoretical work indicating that hot, massive exoplanets may have strong magnetic fields capable of generating radio emission at GHz frequencies. We have detected and confirmed radio flares from the T6.5 dwarf 2MASS J10475385+2124234. This detection dramatically extends the temperature range over which brown dwarfs appear to be at least sporadic radio-emitters, from ~1900 K (L3.5) down to ~900 K (T6.5). It also demonstrates that the utility of radio detection as a unique tool to study the magnetic fields of substellar objects extends to the coolest dwarfs, and, plausibly to hot, massive exoplanets. We have also identified a single, 3.6 sigma flare from the L1 dwarf, 2MASS J1439284+192915. This detection is tentative and requires confirmation by additional monitoring observations.