Swift Detection of a 65 Day X-Ray Period from the Ultraluminous Pulsar NGC 7793 P13
Abstract
NGC 7793 P13 is an ultraluminous X-ray source harboring an accreting pulsar. We report on the detection of a ∼65 day period X-ray modulation with Swift observations in this system. The modulation period found in the X-ray band is P = 65.05 ± 0.10 days and the profile is asymmetric with a fast rise and a slower decay. On the other hand, the u-band light curve collected by Swift UVOT confirmed an optical modulation with a period of P = 64.24 ± 0.13 days. We explored the phase evolution of the X-ray and optical periodicities and propose two solutions. A superorbital modulation with a period of ∼2700-4700 days probably caused by the precession of a warped accretion disk is necessary to interpret the phase drift of the optical data. We further discuss the implication if this ∼65 day periodicity is caused by the superorbital modulation. Estimated from the relationship between the spin-orbital and orbital-superorbital periods of known disk-fed high-mass X-ray binaries, the orbital period of P13 is roughly estimated as 3-7 days. In this case, an unknown mechanism with a much longer timescale is needed to interpret the phase drift. Further studies on the stability of these two periodicities with a long-term monitoring could help us to probe their physical origins.
- Publication:
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The Astrophysical Journal
- Pub Date:
- January 2017
- DOI:
- 10.3847/2041-8213/835/1/L9
- arXiv:
- arXiv:1701.02449
- Bibcode:
- 2017ApJ...835L...9H
- Keywords:
-
- accretion;
- accretion disks;
- galaxies: individual: NGC 7793;
- stars: neutron;
- X-rays: binaries;
- X-rays: individual: NGC 7793 P13;
- CXOU J235750.9-323726;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 5 figures, accepted for publication in the Astrophysical Journal Letter