Confirmation of the 62 Day X-Ray Periodicity from M82

Using 400 days of new X-ray monitoring of M82, we confirm the 62 day periodicity previously reported. In the full data set spanning 1124 days, we find a period of 62.0 +/- 0.3 days and a coherence, Q = 22.3, that is consistent with a strictly periodic signal. We estimate that the probability of chance occurrence of our observed signal is 6E-7. The light curve folded at this period is roughly sinusoidal and has a peak to peak amplitude of (0.99 +/- 0.10) x 10^-11 erg cm^-2 s^-1. Confirmation of the periodicity strengthens our previous suggestion that the 62 day modulation is due to orbital motion within an X-ray binary.