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A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC 7793 P13

Fürst, F. and Walton, D. J. and Heida, M. and Harrison, F. A. and Barret, D. and Brightman, M. and Fabian, A. C. and Middleton, M. J. and Pinto, C. and Rana, V. and Tramper, F. and Webb, N. and Kretschmar, P. (2018) A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC 7793 P13. Astronomy and Astrophysics, 616 . Art. No. A186. ISSN 0004-6361. doi:10.1051/0004-6361/201833292.

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We present a timing analysis of multiple XMM-Newton and NuSTAR observations of the ultra-luminous pulsar NGC 7793 P13 spread over its 65 d variability period. We use the measured pulse periods to determine the orbital ephemeris, confirm a long orbital period with P_(orb) = 63.9^(+0.5)_(−0.6) d, and find an eccentricity of e ≤ 0.15. The orbital signature is imprinted on top of a secular spin-up, which seems to get faster as the source becomes brighter. We also analyze data from dense monitoring of the source with Swift and find an optical photometric period of 63.9 ± 0.5 d and an X-ray flux period of 66.8 ± 0.4 d. The optical period is consistent with the orbital period, while the X-ray flux period is significantly longer. We discuss possible reasons for this discrepancy, which could be due to a super-orbital period caused by a precessing accretion disk or an orbital resonance. We put the orbital period of P13 into context with the orbital periods implied for two other ultra-luminous pulsars, M82 X-2 and NGC 5907 ULX, and discuss possible implications for the system parameters.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fürst, F.0000-0003-0388-0560
Walton, D. J.0000-0001-5819-3552
Heida, M.0000-0002-1082-7496
Harrison, F. A.0000-0003-2992-8024
Barret, D.0000-0002-0393-9190
Brightman, M.0000-0002-8147-2602
Fabian, A. C.0000-0002-9378-4072
Middleton, M. J.0000-0002-8183-2970
Pinto, C.0000-0003-2532-7379
Rana, V.0000-0003-1703-8796
Kretschmar, P.0000-0001-9840-2048
Additional Information:© ESO 2018. Received 24 April 2018 / Accepted 17 May 2018. We would like to thank the referee for the very helpful comments that helped to improve the manuscript. We thank M. Kühnel and M. Nowak for the useful discussions. DJW and MJM acknowledge support from STFC Ernest Rutherford fellowships. This research has made use of data obtained with NuSTAR, a project led by Caltech, funded by NASA and managed by NASA/JPL, and has utilized the nustardas software package, jointly developed by ASDC (Italy) and Caltech (USA). This research has also made use of data obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States. This work has made use of data supplied by the UK Swift Science Data Centre at the University of Leicester, and also of the XRT Data Analysis Software (XRTDAS) developed under the responsibility of the ASI Science Data Center (ASDC), Italy. This research has made use of a collection of ISIS functions (ISISscripts) provided by ECAP/Remeis observatory and MIT (
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:stars: neutron / X-rays: binaries / techniques: radial velocities / accretion / accretion disks / pulsars: individual: NGC 7793 P13
Record Number:CaltechAUTHORS:20180517-190441870
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Official Citation:A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC 7793 P13 F. Fürst, D. J. Walton, M. Heida, F. A. Harrison, D. Barret, M. Brightman, A. C. Fabian, M. J. Middleton, C. Pinto, V. Rana, F. Tramper, N. Webb and P. Kretschmar A&A, 616 (2018) A186 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86447
Deposited By: Joy Painter
Deposited On:18 May 2018 16:48
Last Modified:15 Nov 2021 20:38

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