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

Journal Article · Fri Jan 20 04:00:00 EST 2017 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8213/835/1/L9· OSTI ID:22654562

Hu, Chin-Ping; Ng, C. -Y. ^[1]; Li, K. L. ^[2]; Kong, Albert K. H. ^[3]

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1. Department of Physics, The University of Hong Kong, Pokfulam Road (Hong Kong)
2. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
3. Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

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.

• OSTI ID: 22654562
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 835; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
ASYMMETRY
DETECTION
EVOLUTION
GALAXIES
MASS
MATHEMATICAL SOLUTIONS
MODULATION
NEUTRONS
PERIODICITY
PRECESSION
PULSARS
SPIN
STABILITY
STARS
VISIBLE RADIATION
X RADIATION
X-RAY SOURCES