Swift Detection of a 65 Day X-Ray Period from the Ultraluminous Pulsar NGC 7793 P13

Chin Ping Hu, K. L. Li, Albert K.H. Kong, C. Y. Ng, Lupin Chun Che Lin

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

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.

Original languageEnglish
Article numberL9
JournalAstrophysical Journal Letters
Volume835
Issue number1
DOIs
Publication statusPublished - 2017 Jan 20

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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