LMC X-2
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Dorado |
| Right ascension | 05h 20m 28.2s[1] |
| Declination | −71° 57′ 33″[1] |
| Apparent magnitude (V) | ~18.8[2] |
| Characteristics | |
| Evolutionary stage | Neutron star (A) Evolved B-type star (B) |
| Spectral type | Neutron star + ? |
| Astrometry | |
| Radial velocity (Rv) | 262.2 ± 3.4[3] km/s |
| Distance | ~162,983 ly (~49,970[4] pc) |
| Orbit | |
| Primary | neutron star |
| Companion | main-sequence star |
| Period (P) | 0.32 ± 0.02 days[5] (8.15 hours) |
| Inclination (i) | ≲70[6]° |
| Semi-amplitude (K2) (secondary) | 315 ± 28[7] km/s |
| Details | |
| A | |
| Mass | 1.4 ± 0.6[8] M☉ |
| Radius | ≲16 km[9] R☉ |
| Temperature | 2,300,000 ± 900,000[9] K |
| B | |
| Mass | ≤1[10] M☉ |
| Other designations | |
LMC X-2, SWIFT J0520.9-7156[11] | |
| Database references | |
| SIMBAD | data |
LMC X-2 is a Low-mass X-ray binary (LMXB) located in the Large Magellanic Cloud (LMC), a satellite galaxy of Milky Way. It is one of the five brightest X-ray sources in the LMC and is the most luminous LMXB with a luminosity ranging from 0.3×10³⁷ and 6×10³⁸ ergs s⁻¹.[12] This binary system consist of a neutron star accreating matter from an orbiting low-mass blue star.[13] Its high luminosity is caused because of its X-ray emission is close to the Eddington limit or Eddington luminosity for a neutron star and because the Large Magellanic Cloud has lower metal abundances, allowing for higher Eddington luminosities and a higher accretion rate causing its high luminosity.[14][15][16]
LMC X-2 is classified as a Z-source, a subtype of neutron star LMXB characterized by high accretion rates and a distinctive Z-shaped track in X-ray color-color and hardness-intensity diagrams. These tracks reflect transitions between three spectral states: the horizontal branch, normal branch, and flaring branch. It is the first Z-source identified outside the Milky Way, making it the eighth known Z-source overall.[17][18]
Discovery
Main system
The main system of LMC X-2 was discovered around January of 1971 by the Uhuru satellite during early satellite flights that identified the system as a point in the LMC along with 2 other points, which are now known as the supersoft X-ray binaries (SSXB) CAL 83 and CAL 87.[19][20]
Characteristics
System Characteristics
LMC X-2 consists of a neutron star and a companion evolved B-type star. The companion star orbits the neutron star in 8.15 hours from an inclination of around 70°[6][21], it's semi-major axis along with the eccentricity is unknown from the lack of orbital information and observations.
Observation
LMC X-2 is has been extensively studied by multiple X-ray observatories:
- Four observations from Rossi X-ray Timing Explorer (RXTE) revealed the complete Z-diagram, confirming its Z-source classification through spectral state transitions and quasi-periodic oscillations.[22]
- Archival data from XMM-Newton provided high-precision spectral analysis, with models incorporating blackbody emission (neutron star surface, ~1-2 keV) and Comptonization (corona). Luminosities indicate near-Eddington accretion.[23]
- Approximately 140 ks of observations from Astrosat captured broad-band X-ray spectral evolution, showing changes in disk temperature, electron temperature, and optical depth along the Z-track.[24]
- Other Observations from MAXI and Swift Space Telescope indicates persistent emission with occasional flares. No definitive orbital period has been identified despite photometric searches.[25]
See also
References
- ↑ 1.0 1.1 https://www.aanda.org/articles/aa/pdf/2008/04/aa8027-07.pdf
- ↑ McGowan, K. E.; Charles, P. A.; O'Donoghue, D.; Smale, A. P. (November 2003). "Correlated optical and X-ray variability in LMC X-2". Monthly Notices of the Royal Astronomical Society. 345 (3): 1039–1048. arXiv:astro-ph/0307373. Bibcode:2003MNRAS.345.1039M. doi:10.1046/j.1365-8711.2003.07029.x.
- ↑ "Kinematical Structure of the Magellanic System - R.P. van der Marel et al". ned.ipac.caltech.edu. Retrieved 2025-10-11.
- ↑ https://www.researchgate.net/publication/235881281_An_eclipsing-binary_distance_to_the_Large_Magellanic_Cloud_accurate_to_two_per_cent
- ↑ Cornelisse, R.; Steeghs, D.; Casares, J.; Charles, P. A.; Shih, I. C.; Hynes, R. I.; O'Brien, K. (October 2007). "A signature of the donor star in the extra-galactic X-ray binary LMC X−2". Monthly Notices of the Royal Astronomical Society. 381 (1): 194–200. arXiv:0707.2018. Bibcode:2007MNRAS.381..194C. doi:10.1111/j.1365-2966.2007.12233.x. ISSN 0035-8711.
- ↑ 6.0 6.1 https://academic.oup.com/mnras/article/316/4/729/1084536https://academic.oup.com/mnras/article/316/4/729/1084536#:~:text=1.1,1988).
- ↑ Cornelisse, R.; Steeghs, D.; Casares, J.; Charles, P. A.; Shih, I. C.; Hynes, R. I.; O'Brien, K. (2007). "A signature of the donor star in the extra-galactic X-ray binary LMC X−2". Monthly Notices of the Royal Astronomical Society. 381 (1): 194–200. arXiv:0707.2018. Bibcode:2007MNRAS.381..194C. doi:10.1111/j.1365-2966.2007.12233.x.
- ↑ Smale, Alan P.; Kuulkers, Erik (2000). "LMC X-2: The First Extragalactic Z Source?". The Astrophysical Journal. 528 (2): 702–710. arXiv:astro-ph/9907303. Bibcode:2000ApJ...528..702S. doi:10.1086/308193.
- ↑ 9.0 9.1 https://www.aanda.org/articles/aa/pdf/2008/04/aa8027-07.pdf
- ↑ Crampton, D.; Hutchings, J. B.; Cowley, A. P.; Schmidtke, P. C.; Thompson, I. B. (June 1990). "The low-mass X-ray binary LMC X-2". pp. 496–500.
- ↑ "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2025-10-08.
- ↑ Bonnet-Bidaud, J. M.; Motch, C.; Beuermann, K.; Pakull, M.; Parmar, A. N.; Van Der Klis, M. (1989). "LMC X-2 : An extragalactic bulge-type source". Astronomy and Astrophysics. 213: 97. Bibcode:1989A&A...213...97B.
- ↑ Ishioka, Ryoko; Chu 朱有, You-Hua 花.; Points, Sean D.; Li 李傳, Chuan-Jui 睿.; Chen, Chen-Hung (2020). "A Binary Star in the Superbubble N160 in the Large Magellanic Cloud". The Astrophysical Journal. 900 (2): 195. Bibcode:2020ApJ...900..195I. doi:10.3847/1538-4357/aba8f2.
- ↑ Pakull, M. (1979). "Probable optical identification of LMC X-2". The Messenger. 16: 38. Bibcode:1979Msngr..16...38P.
- ↑ [1]
- ↑ Greene, J.; Wachter, S.; Smale, A. P. (May 1999). "LMC X-2: The Search for the Orbital Period". American Astronomical Society Meeting Abstracts #194. 194: 52.16. Bibcode:1999AAS...194.5216G.
- ↑ Smale, Alan P.; Kuulkers, Erik (2000-01-10). "LMC X-2: The First Extragalactic Z Source?". The Astrophysical Journal. 528 (2): 702–710. arXiv:astro-ph/9907303. Bibcode:2000ApJ...528..702S. doi:10.1086/308193. ISSN 0004-637X.
- ↑ "LMC X-2". maxi.riken.jp. Retrieved 2025-10-11.
- ↑ https://academic.oup.com/mnras/article/316/4/729/1084536
- ↑ Schmidtke, P. C.; Cowley, A. P.; Frattare, L. M.; McGrath, T. K.; Hutchings, J. B.; Crampton, D. (1994). "LMC Stellar X-Ray Sources Observed with ROSAT: I. X-Ray Data and Search for Optical Counterparts". Publications of the Astronomical Society of the Pacific. 106: 843. Bibcode:1994PASP..106..843S. doi:10.1086/133452.
- ↑ Cornelisse, R.; Steeghs, D.; Casares, J.; Charles, P. A.; Shih, I. C.; Hynes, R. I.; O'Brien, K. (October 2007). "A signature of the donor star in the extra-galactic X-ray binary LMC X−2". Monthly Notices of the Royal Astronomical Society. 381 (1): 194–200. arXiv:0707.2018. Bibcode:2007MNRAS.381..194C. doi:10.1111/j.1365-2966.2007.12233.x. ISSN 0035-8711.
- ↑ White, Nicholas E.; Smale, A. P.; Homan, J.; Kuulkers, E. (2003-01-30). "The Complete Z-diagram of LMC X-2".
- ↑ Lavagetto, G.; Iaria, R.; D'Aì, A.; Salvo, T. Di; Robba, N. R. (2008-01-01). "Spectral analysis of LMC X–2 with XMM/Newton: unveiling the emission process in the extragalactic Z-source". Astronomy & Astrophysics. 478 (1): 181–186. arXiv:0710.4934. Bibcode:2008A&A...478..181L. doi:10.1051/0004-6361:20078027. ISSN 0004-6361.
- ↑ Agrawal, V K; Nandi, Anuj (2020-09-21). "AstroSat view of LMC X-2: evolution of broad-band X-ray spectral properties along a complete Z-track". Monthly Notices of the Royal Astronomical Society. 497 (3): 3726–3733. doi:10.1093/mnras/staa2063. ISSN 0035-8711.
- ↑ Greene, J.; Wachter, S.; Smale, A. P. (May 1999). "LMC X-2: The Search for the Orbital Period". American Astronomical Society Meeting Abstracts #194. 194: 52.16. Bibcode:1999AAS...194.5216G.
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