Statistical analysis of radio-flaring brown dwarf population

Brown dwarfs are referred to as “failed stars” because they lack central hydrogen burning. They serve as a link between planets and stars. Some brown dwarfs have been discovered to have kilogauss magnetic fields and flare radio emissions, similar to aurora on magnetised planets in our solar system, pique astronomers’ interest in their field properties and dynamics.

Brown dwarf radio emissions reflect their magnetic activities. Radio, optical, and X-ray emissions are all used as magnetic indicators for solar-type stars, whereas for brown dwarfs, optical and X-ray emissions decrease dramatically, and radio becomes the most efficient probe.

Dr. Tang Jing and her colleagues from the Chinese Academy of Sciences’ National Astronomical Observatories (NAOC) conducted a statistical analysis of a radio-flaring brown dwarf population, which helped quantify the potential for finding such objects in FAST surveys.

This research was published in the journal Research in Astronomy and Astrophysics.

The traditional method of studying brown dwarfs is to pick a few of them and track them for several hours to catch any flares, which is very expensive. Until now, there have been fewer than 20 detected flaring brown dwarfs. According to the study, the so-called Commensal Radio Astronomy FAST Survey (CRAFTS) promises to increase the number by nearly one order of magnitude.

CRAFTS, led by Dr. Li Di, FAST’s chief scientist, employs a novel and unprecedented mode to achieve simultaneous data collection for pulsar and FRB search, Galactic HI mapping, and HI galaxy study. In drift-scan mode, it is designed to cover 60% of the sky.

The most significant issue for FAST in locating a point source is the confusion caused by the large beam size. The flaring radio emission, on the other hand, is highly circularly polarised, causing little confusion. Circular polarisation can be calculated from orthogonally polarised outputs, regardless of system fluctuation, and is an effective method for searching for flares.

Cross-matching the archival optical/infrared counterpart can be used for identification if some highly circularly polarised signals are found in the survey. FAST should be able to detect flaring brown dwarfs as far away as 180 pc.

The majority of flaring brown dwarfs can be detected at high frequencies. Despite some efforts in low frequencies, flaring emission in the L band has yet to be detected. FAST could fill this void. If the mission is successful, it bodes well for FAST’s ability to discover exoplanets with strong magnetic fields.