A 78 Day X-Ray Period Detected from NGC 5907 ULX1 by Swift

Creators: Walton, D. J.; Fürst, F.; Bachetti, M.; Barret, D.; Brightman, M.; Fabian, A. C.; Gehrels, N.; Harrison, F. A.; Heida, M.; Middleton, M. J.; Rana, V.; Roberts, T. P.; Stern, D.; Tao, L.; Webb, N.

Abstract

We report the detection of a 78.1 ± 0.5 day period in the X-ray light curve of the extreme ultraluminous X-ray source NGC 5907 ULX1 (L_X,peak ~ 5 x 10^(40) erg s^(−1)), discovered during an extensive monitoring program with Swift. These periodic variations are strong, with the observed flux changing by a factor of ~3–4 between the peaks and the troughs of the cycle; our simulations suggest that the observed periodicity is detected comfortably in excess of 3σ significance. We discuss possible origins for this X-ray period, but conclude that at the current time we cannot robustly distinguish between orbital and super-orbital variations.

Additional Information

© 2016 The American Astronomical Society. Received 2016 June 27; revised 2016 July 20; accepted 2016 July 22; published 2016 August 5. The authors would like to thank the reviewer for their timely and positive feedback, which helped to improve the final manuscript. A.C.F. acknowledges support from ERC Advanced Grant 340442. The work of D.J.W./D.S. was performed at JPL/Caltech, under contract with NASA. D.B. and N.W. acknowledge financial support from the French Space Agency (CNES), M.J.M. acknowledges support from an Ernest Rutherford STFC fellowship, and T.P.R. acknowledges support from the STFC consolidated grant ST/L00075X/1. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester, and also made use of the XRT Data Analysis Software (XRTDAS) developed under the responsibility of the ASI Science Data Center (ASDC), Italy. We acknowledge the use of public data from the Swift data archive. This research has also made use of a collection of ISIS functions (ISISscripts) provided by ECAP/Remeis observatory and MIT. Facility: Swift. -

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