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Title: A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC7793 P13
Authors: Fürst, F.
Walton, D.J.
Rana, V
+10 Co-Authors
Keywords: stars: neutron
X-rays: binaries
techniques: radial velocities
accretion disks
pulsars: individual: NGC 7793 P13
Issue Date: Sep-2018
Publisher: EDP Sciences for European Southern Observatory
Citation: Astronomy & Astrophysics, 2018, Vol.616, p10
Abstract: 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 Porb = 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.
Description: Restricted Access
ISSN: 0004-6361
1432-0746 (Online)
Alternative Location:
Copyright: 2018 European Southern Observatory
Appears in Collections:Research Papers (A&A)

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