AT 2017fvz: a nova in the dwarf irregular galaxy NGC 6822

A transient in the Local Group dwarf irregular galaxy NGC6822 (Barnard's Galaxy) was discovered on 2017 August 2 and is only the second classical nova discovered in that galaxy. We conducted optical, near-ultraviolet, and X-ray follow-up observations of the eruption, the results of which we present here. This 'very fast' nova had a peak V-band magnitude in the range -7.41 > M-V >-8.33 mag, with decline times of t(2,V) = 8.1 +/- 0.2 d and t(3,V) = 15.2 +/- 0.3 d. The early- and late-time spectra are consistent with an Fe II spectral class. The Ha emission line initially has a full width at half-maximum intensity of similar to 2400 km s(-1) - a moderately fast ejecta velocity for the class. The Ha line then narrows monotonically to similar to 1800 km s(-1) by 70 d post-eruption. The lack of a pre-eruption coincident source in archival Hubble Space Telescope imaging implies that the donor is a main-sequence, or possibly subgiant, star. The relatively low-peak luminosity and rapid decline hint that AT 2017fvz may be a 'faint and fast' nova.