Faint debris disk peering through 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 echos from an inner ($r < 1~{\rm au}$) debris disk with a total mass down to that of the solar system's zodiacal dust are expected to emerge at wavelengths longer than $\sim 10~{\rm \mu m}$ with a strength comparable to or greater than a white-light superflare. Also, observable echos from inner- ($r \lesssim 0.5~{\rm au}$) debris disks irradiated by energetic ($\gtrsim 10^{33.5}~{\rm ergs}$) superflares of nearby ($D < 3~{\rm pc}$) 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.