Identify the emission mechanism of the HD 283572 millimeter flare

Determine whether the 225 GHz millimeter flare emission observed from the young class III star HD 283572 on 2022 Jan 17 is produced by optically thin synchrotron radiation or by gyro-synchrotron radiation from non-thermal electrons in the stellar magnetosphere.

Background

The authors find consistently steep and negative millimeter spectral indices during both the active-quiescent period and the flare (e.g., α = −2.7 ± 1.2 over the full track), and brightness temperatures in the range 10^8–10^10 K, indicating non-thermal processes. They consider both synchrotron and gyro-synchrotron mechanisms, using spectral slopes and polarization constraints.

A null detection of linear polarization nominally disfavors synchrotron, but magnetic field strengths required for gyro-synchrotron to peak near 225 GHz (∼9 kG for γ ≈ 3) appear too high for typical young star fields, leading to conflicting evidence. The authors therefore cannot determine the mechanism with the available data.