We report the discovery and classification of SDSS J053341.43+001434.1 ( SDSS0533 ) , an early-L dwarf first discovered during a powerful \Delta V < -11 magnitude flare observed as part of the ASAS-SN survey .
Optical and infrared spectroscopy indicate a spectral type of L0 with strong H \alpha emission and a blue NIR spectral slope .
Combining the photometric distance , proper motion , and radial velocity of SDSS0533 yields three-dimensional velocities of ( U,V,W ) = ( 14 \pm 13 , -35 \pm 14 , -94 \pm 22 ) km s ^ { -1 } , indicating that it is most likely part of the thick disk population and probably old .
The three detections of SDSS0533 obtained during the flare are consistent with a total V -band flare energy of at least 4.9 \times 10 ^ { 33 } ergs ( corresponding to a total thermal energy of at least E _ { tot } > 3.7 \times 10 ^ { 34 } erg ) , placing it among the strongest detected M dwarf flares .
The presence of this powerful flare on an old L0 dwarf may indicate that stellar-type magnetic activity persists down to the end of the main sequence and on older ML transition dwarfs .