Superorbital period variations in the X-ray pulsar LMC X-4

Abstract

We report the discovery of a decay in the superorbital period of the binary X-ray pulsar LMC X-4. Combining archival data and published long term X-ray light curves, we have found a decay in the third period in this system (P ~ 30:3 day, P P ~ -2x10-5 s s-1). Along with this result, a comparison of the superorbital intensity variations in LMC X-4, Her X-1 and SMC X-1 is also presented.