LMC P3

LMC P3

Image of Gamma ray Binary LMC P3 (Circled) within Supernova Remnant DEM L241
Observation data
Epoch J2000      Equinox J2000
Constellation Dorado
Right ascension 05h 35m 0s
Declination −67° 35′ 11″
Characteristics
Evolutionary stage Main-sequence + Neutron Star
Spectral type O5III(f)
Astrometry
Radial velocity (Rv)13.5 km/s
Distance163,000 ly
(50,589 pc)
Orbit
Primarymain-sequence star
Secondarycompact object
Period (P)10.301 days
Semi-major axis (a)0.3 au
Eccentricity (e)0.4 ± 0.07
Inclination (i)69.8° ± 0.84°
Semi-amplitude (K2)
(secondary)		10.69 ± 1.23 km/s
Details
A
Mass33.5 M☉
Radius14.5 R☉
Temperature33,000 K
B
Mass1.4 M☉
Other designations
LMC P3, 4FGL J0535.2-6736, CXOU J053600.0-673507
Database references
SIMBADdata

LMC P3 (also known as 4FGL J0535.2-6736) is a gamma-ray binary star system located in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way Galaxy approximately 163,000 light-years from Earth. It is the first gamma-ray binary discovered outside the Milky Way and the most luminous such system known, with gamma-ray emissions exceeding 10³⁶ ergs per second in the high-energy (HE) range above 100 MeV. The system consists of a massive O-type star orbiting a compact object, likely a neutron star, in an eccentric 10.3-day orbit, producing periodic high-energy emissions through interactions between the stellar wind and relativistic particles from the compact object. LMC P3 resides within the supernova remnant DEM L241 and serves as a key object for studying particle acceleration and binary evolution in low-metallicity environments.

Discovery

LMC P3 was initially identified as a high-mass X-ray binary (HMXB) in 2012 through observations with NASA's Chandra X-ray Observatory, located within the supernova remnant DEM L241 in the LMC. In 2015, analysis of data from NASA's Fermi Gamma-ray Space Telescope revealed a 10.301-day periodicity in gamma-ray emissions, confirming its classification as a gamma-ray binary—the first detected beyond the Milky Way. This discovery stemmed from a broader study of gamma-ray sources in the LMC, highlighting LMC P3 as an exceptionally powerful emitter. Follow-up observations across multiple wavelengths, including X-rays (via NASA's Neil Gehrels Swift Observatory and ESA's XMM-Newton), radio (Australia Telescope Compact Array), and optical (Southern Astrophysical Research Telescope), further characterized the system.

Very high-energy (VHE) gamma-ray emissions above 100 GeV were detected in 2017 using the High Energy Stereoscopic System (H.E.S.S.) telescope array in Namibia, marking LMC P3 as the first extragalactic VHE gamma-ray binary. These observations showed variability tied to the orbital phase, with VHE emissions occurring during approximately 20% of the orbit.

Characteristics

The binary system comprises an O5 III blue supergiant star, with an estimated mass of 33.5 solar masses and a surface temperature over 33,000 °C (60,000 °F), orbiting a compact object that is likely a neutron star with a mass around 1.4 solar masses. The massive supergiant star expels a dense stellar wind at speeds of millions of miles per hour, while the compact object accelerates particles to relativistic speeds, possibly via a pulsar wind or jets.

The supernova remnant DEM L241 is believed to be the birthplace of the compact object, formed from the explosion of a massive progenitor star.

Emissions

Emissions from LMC P3 span radio, optical, X-ray, and gamma-ray wavelengths, modulated by the orbital cycle:

  • Gamma-ray Emissions: Detected by Fermi at energies above 100 MeV and VHE emissions above 100 GeV, observed by H.E.S.S., occur near inferior conjunction (orbital phases 0.2–0.4) and are anti-correlated with HE emissions.
  • X-ray Emissions: Variable X-ray flux observed by Chandra, Swift, and XMM-Newton, peaking at periastron when the compact object interacts with the stellar disk.

See also

References

  1. 1 2 3 Abdalla, H.; et al. (2018). "Detection of variable VHE γ-ray emission from the extra-galactic γ-ray binary LMC P3". Astronomy & Astrophysics. 610: L17. arXiv:1801.06322. Bibcode:2018A&A...610L..17H. doi:10.1051/0004-6361/201732426.
  2. 1 2 3 4 5 6 7 8 9 Soelen, B. van; Komin, N.; Kniazev, A.; Väisänen, P. (2019-02-27). "The orbital parameters of the gamma-ray binary LMC P3". Monthly Notices of the Royal Astronomical Society. 484 (3): 4347–4351. arXiv:1901.08911. doi:10.1093/mnras/stz289.
  3. 1 2 3 4 5 "NASA's Fermi Finds Record-breaking Binary in Galaxy Next Door - NASA". 2016-09-29. Retrieved 2025-10-01.
  4. ↑ "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2025-09-29.
  5. ↑ "NASA's Fermi Finds Record-breaking Binary in Galaxy Next Door - NASA". 2016-09-29. Retrieved 2025-09-29.
  6. ↑
  7. 1 2 Fisher, Lalenthra Tamlyn; et al. (2023). "H.E.S.S. Observations of the Gamma-ray Binary LMC P3". Proceedings of 38th International Cosmic Ray Conference — PoS(ICRC2023). p. 906. doi:10.22323/1.444.0906.
  8. ↑ "New Fermi observations: discovery of a new gamma binary – Institut de Recherche en Astrophysique et Planétologie". www.irap.omp.eu. Retrieved 2025-10-01.
  9. 1 2 Komin, Nukri; Haupt, Maria (2017). "Discovery of VHE Gamma-Ray Emission from the Binary System LMC P3". Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017). p. 730. doi:10.22323/1.301.0730.