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A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC7793 P13

A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC7793 P13
A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC7793 P13
We present a timing analysis of multiple XMM-Newton and NuSTAR observations of the ultra-luminous pulsar NGC 7793 P13 spread over its 65d 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 analyse 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.
0004-6361
1-10
Fürst, Felix
859045eb-4966-4cea-8f48-28c832d162f3
Walton, D.J.
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Heida, M.
fc66bb37-4c8d-4fc5-9af4-2e7438e45fcd
Barret, D.
343cdacd-9683-4f70-910b-6539201daf06
Brightman, M.
eb110ae1-9a2c-4968-b9ef-e7955feba535
Fabian, A.C.
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Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad
Fürst, Felix
859045eb-4966-4cea-8f48-28c832d162f3
Walton, D.J.
a1a36b18-a77b-48e8-8665-45bbef0c7bd1
Heida, M.
fc66bb37-4c8d-4fc5-9af4-2e7438e45fcd
Barret, D.
343cdacd-9683-4f70-910b-6539201daf06
Brightman, M.
eb110ae1-9a2c-4968-b9ef-e7955feba535
Fabian, A.C.
0c353376-f159-4129-b03e-d3993c0c5406
Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad

Fürst, Felix, Walton, D.J., Heida, M., Barret, D., Brightman, M., Fabian, A.C. and Middleton, Matthew (2018) A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC7793 P13. Astronomy & Astrophysics, 616, 1-10, [A186]. (doi:10.1051/0004-6361/201833292).

Record type: Article

Abstract

We present a timing analysis of multiple XMM-Newton and NuSTAR observations of the ultra-luminous pulsar NGC 7793 P13 spread over its 65d 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 analyse 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.

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Accepted/In Press date: 13 May 2018
e-pub ahead of print date: 10 September 2018

Identifiers

Local EPrints ID: 421335
URI: http://eprints.soton.ac.uk/id/eprint/421335
ISSN: 0004-6361
PURE UUID: 8f6d4ecb-e125-401b-9bf5-9f76711c645b

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Date deposited: 01 Jun 2018 16:30
Last modified: 16 Dec 2019 18:12

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