TESS Observations of Outbursts on Polars—Superflares

Abstract

Flare events are magnetic activities on the stellar surface, which can provide us with information about the accretion behavior and evolution of polars. In this paper, we search for flare events on polars from all the available 2 minute cadence TESS data through visual inspection, and identify six flare events on five flaring stars from 185 polars. All the flares have bolometric energies above 1034 erg, with a median of ∼1035 erg, so they are superflares. Among them, two flares are followed by a brightness enhancement, which may suggest an accretion burst on the white dwarf caused by a coronal mass ejection. A completeness analysis of the detections demonstrates that the flare activities on the low-mass red dwarfs of polars are very similar to those on M dwarfs, which indicates that the highly magnetic fields of the white dwarfs have no significant effect on the magnetic activities on polars. We estimate that another ∼20–30 polars include a magnetically active secondary star, and more intensive searching for flares on polars is encouraged in further work.