A possible 55-d X-ray period of the ultraluminous accreting pulsar M82 X-2

Abstract

We report on the possible detection of a 55-d X-ray modulation for the ultraluminous accretingpulsar M82 X-2 from archival Chandra observations. Because M82 X-2 is known to havea 2.5-d orbital period, if the 55-d period is real, then it will be the superorbital period of thesystem. We also investigated variabilities of three other nearby ultraluminous X-ray sourcesin the central region of M82 with the Chandra data, and we did not find any evidence ofperiodicities. Furthermore, we re-examined the previously reported 62-d periodicity near thecentral region of M82 by performing a systematic timing study with all the archival RossiX-Ray Timing Explorer and Swift data. Using various dynamic timing analysis methods, wehave confirmed that the 62-d period is not stable, suggesting that it is not the orbital period ofM82 X-1; this is in agreement with previous work.