Data from Discovery of a Surprising Flux Event in White Dwarf HZ 4

HZ 4 is a DA3.4C White Dwarf (WD) and a commonly-used photometric standard star. While analyzing its suitability as a calibrator, data from TESS revealed an increase in flux by 43.2%, seen only on Sector 43 observed in September and October of 2021. The event duration is 28.8 hours, and the light curve shape is approximately symmetric and consists of a flux increase preceded and followed by a flux decrease of 11.4%. If periodic, the period would be >77 days. No other objects are observed in the DSS, GALEX, or WISE images within the TESS pixel in which HZ 4 resides. The event resembles the flux increases of long-lived white dwarf pulsators, although HZ4 is not in the instability strip. There is no evidence of a binary companion, which suggests HZ4 is not a dwarf nova, nor photometric evidence of any circumstellar material.