Ground-based detection of G star superflares with NGTS.

We present high cadence detections of two superflares from a bright G8 star (V = 11.56) with the Next Generation Transit Survey (NGTS).We improve upon previous super are detections by resolving the flare rise and peak, allowing us to fit a solar flare inspired model without the need for arbitrary break points between rise and decay. Our data also enables us to identify substructure in the flares. From changing star-spot modulation in the NGTS data, we detect a stellar rotation period of 59 h, along with evidence for differential rotation. We combine this rotation period with the observed ROSATX-ray flux to determine that the star's X-ray activity is saturated. We calculate the flare bolometric energies as 5.4+0.8-0.7 x 1034 and 2.6+0.4-0.3 x 1034 erg and compare our detections with G star superflares detected in the Kepler survey. We find our main flare to be one of the largest amplitude superflares detected from a bright G star. With energies more than 100 times greater than the Carrington event, our flare detections demonstrate the role that ground-based instruments such as NGTS can have in assessing the habitability of Earth-like exoplanets, particularly in the era of PLATO. [ABSTRACT FROM AUTHOR]