LMC P3
Gamma-ray Binary in the Large Magellanic Cloud
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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.[5][2] 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. [6][7]
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[1] |
| Declination | −67° 35′ 11″[1] |
| Characteristics | |
| Evolutionary stage | Main-sequence + Neutron Star |
| Spectral type | O5III(f) |
| Astrometry | |
| Radial velocity (Rv) | 13.5[2] km/s |
| Distance | 163,000[3] ly (50,589 pc) |
| Orbit | |
| Primary | main-sequence star |
| Name | compact object |
| Period (P) | 10.301 days[2] |
| Semi-major axis (a) | 0.3 au[2] |
| Eccentricity (e) | 0.4 ± 0.07[2] |
| Inclination (i) | 69.8° ± 0.84° |
| Semi-amplitude (K2) (secondary) | 10.69 ± 1.23[2] km/s |
| Details[2] | |
| A | |
| Mass | 33.5 M☉ |
| Radius | 14.5 R☉ |
| Temperature | 33,000 K |
| B | |
| Mass | 1.4 M☉ |
| Other designations | |
| LMC P3, 4FGL J0535.2-6736, CXOU J053600.0-673507[4] | |
| Database references | |
| SIMBAD | data |
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.[8][2][3]
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.[7][9]
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.[2]
The supernova remnant DEM L241 is believed to be the birthplace of the compact object, formed from the explosion of a massive progenitor star.[3]
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.[3][1][9]
- 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.[3]
Significance
As the most luminous gamma-ray binary outside our Milky Way, LMC P3 challenges models of binary formation and evolution, particularly in the LMC's lower-metallicity environment compared to the Milky Way. It provides insights into high-energy astrophysics, including the transition from HMXBs to gamma-ray binaries and the role of rapid neutron star spins in sustaining emissions. Ongoing monitoring with instruments like MeerKAT and future telescopes continues to refine understanding of its behavior.[2][3]