Using data acquired with Fine Guidance Sensor #3 on board the Hubble Space Telescope we find that the brightness of Proxima Centauri varies with an amplitude of 0.01 magnitude and a period P=41.6 ± 0.6 days. We interpret this variation as rotational modulation of star spots or bright regions in the photosphere of Proxima Centauri. In a total of 89.36 minutes of monitoring over 212 days, we detected one major flare and three post-flare brightenings.
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Benedict et al. (1993) studied this question.