2018ApJ...861...76P

We present photometric measurements of two superflares observed on a very young brown dwarf, CFHT-BD-Tau 4, observed during Campaign 13 of the Kepler K2 mission. The stronger of the two superflares brightened by a factor of ∼48 relative to the quiescent photospheric level, with an increase in Kepler magnitude Δ\tildeK_p=-4.20. It has an equivalent duration of ∼107 hr, a flare duration of 1.7 days, and an estimated total bolometric (ultraviolet/optical/infrared) energy up to 2.1 x 10³⁸ erg. The weaker of the two superflares is a complex (multipeaked) flare with an estimated total bolometric (UV/optical/IR) energy up to 4.7 x 10³⁶ erg. They are the strongest flares observed on any brown dwarf so far. The flare energies are strongly dependent on the value of the visual extinction parameter A_V used for extinction correction. If we apply a solar flare model to interpret the two superflares, we find that the magnetic fields are required to be stronger by as much as an order of magnitude than previous reports of field measurements in CFHT-BD-Tau 4 by Reiners et al. On the other hand, if we interpret our data in terms of accretion, we find that the requisite rate of accretion for the stronger superflare exceeds the rates that have been reported for other young brown dwarfs.