Faint Debris Disk Peering through the Superflare Light Echo

Abstract

We present the detectability of strong mid-infrared (MIR) light echoes from faint debris disks illuminated by bright superflares of M-dwarf stars. Circumstellar dust grains around an M-dwarf star are simultaneously heated by superflare radiation. One can thus expect their re-emission in the MIR wavelength regime. According to our model calculations for the Proxima Centauri system, the nearest M-dwarf star system, thermal emission echoes from an inner (r < 1 au) debris disk with a total mass down to that of the solar system’s zodiacal dust are expected to emerge at wavelengths longer than ∼10 μm with a strength comparable to or greater than a white-light superflare. Also, observable echoes from inner- (r ≲ 0.5 au) debris disks irradiated by energetic ( ≳1033.5 erg) superflares of nearby (D < 3 pc) M dwarfs are expected. Our simulation results indicate that superflare monitoring using high-speed optical instruments like OASES and its prompt follow-up using ground-based MIR instruments, such as TAO/MIMIZUKU, can detect these MIR light echoes from debris disks around solar neighborhood flare stars.