Discovery of coherent pulsations from the ultraluminous X-ray source NGC 7793 P13

Journal Article · Thu Nov 10 04:00:00 EST 2016 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8205/831/2/L14· OSTI ID:22868494

Fürst, F.; Walton, D. J.; Harrison, F. A.; Brightman, M.; Grefenstette, B.; Madsen, K. K.; Rana, V. ^[1]; Stern, D. ^[2]; Barret, D.; Webb, N. ^[3]; Fabian, A. C. ^[4]; Middleton, M. J. ^[5]; Miller, J. M. ^[6]; Pottschmidt, K. ^[7]

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1. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
3. IRAP/CNRS, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, France and Université de Toulouse III Paul Sabatier/OMP, Toulouse (France)
4. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)
5. Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom)
6. Department of Astronomy, The University of Michigan, Ann Arbor, MI 48109 (United States)
7. CRESST, Department of Physics, and Center for Space Science and Technology, UMBC, Baltimore, MD 21250 (United States)

We report the detection of coherent pulsations from the ultraluminous X-ray source (ULX) NGC 7793 P13. The ≈0.42 s nearly sinusoidal pulsations were initially discovered in broadband X-ray observations using XMM-Newton and NuSTAR taken in 2016. We subsequently also found pulsations in archival XMM-Newton data taken in 2013 and 2014. The significant (≫5σ) detection of coherent pulsations demonstrates that the compact object in P13 is a neutron star, and given the observed peak luminosity of ≈10{sup 40} erg s{sup −1} (assuming isotropy), it is well above the Eddington limit for a 1.4 M{sub ⊙} accretor. This makes P13 the second ULX known to be powered by an accreting neutron star. The pulse period varies between epochs, with a slow but persistent spin-up over the 2013–2016 period. This spin-up indicates a magnetic field of B ≈ 1.5 × 10{sup 12} G, typical of many Galactic accreting pulsars. The most likely explanation for the extreme luminosity is a high degree of beaming; however, this is difficult to reconcile with the sinusoidal pulse profile.

• OSTI ID: 22868494
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 831; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
ISOTROPY
LUMINOSITY
MAGNETIC FIELDS
NEUTRON STARS
PULSARS
PULSATIONS
SPIN
X RADIATION
X-RAY SOURCES