LMC X-2

LMC X-2

Observation data
Epoch J2000      Equinox J2000
Constellation Mensa[1]
Right ascension 05h 20m 28.2s[2]
Declination −71° 57′ 33″[2]
Apparent magnitude (V) ~18.8[3]
Characteristics
Evolutionary stage Neutron star (A)
Evolved B-type star (B)
Spectral type Neutron star + ?
Astrometry
Radial velocity (Rv)262.2 ± 3.4[4] km/s
Distance~162,983 ly
(~49,970[5] pc)
Orbit
Primaryneutron star
Namemain-sequence star
Period (P)0.32 ± 0.02 days[6]
 (8.15 hours)
Inclination (i)≲70[7]°
Semi-amplitude (K2)
(secondary)		315 ± 28[8] km/s
Details
A
Mass1.4 ± 0.6[9] M☉
Radius≲16 km[2] R☉
Temperature2,300,000 ± 900,000[2] K
B
Mass≤1[10] M☉
Radius6-10 km[11] R☉
Other designations
LMC X-2, SWIFT J0520.9-7156[12]
Database references
SIMBADdata

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.[13] This binary system consist of a neutron star accreating matter from an orbiting low-mass blue star.[14] 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.[15][16][17]

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.[18][19]

Discovery

Main system

The main system of LMC X-2 was discovered around January 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.[20][21]

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°,[7][6] its semi-major axis along with the eccentricity is unknown from the lack of orbital information and observations.

Physical Characteristics

Neutron star

This neutron star is the main star of the system LMC X-2, this has a diameter around 16 kilometers and a solar mass of 1.4 ± 0.6[2] by using the X-ray data of LMC X-2 and fit the data in a theoretical blackbody model which relates to the mass and radius along with its temperature.[22]

Companion star

The companion star of LMC X-2 is quite unknown because of it being outshined by the neutron star it is orbiting, this only has information of the mass and radius of around 1 solar masses and 6 to 10 solar radii.[11][10]

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.[23]
  • 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.[24]
  • 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.[25]
  • Other Observations from MAXI and Swift Space Telescope indicates persistent emission with occasional flares. No definitive orbital period has been identified despite photometric searches.[17]

See also

References

  1. ^ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. ^ a b c d e Lavagetto, G.; Iaria, R.; d'Aì, A.; Di Salvo, T.; Robba, N. R. (2008). "Spectral analysis of LMC X–2 with XMM/Newton: unveiling the emission process in the extragalactic Z-source" (PDF). Astronomy & Astrophysics. 478: 181–186. Bibcode:2008A&A...478..181L. doi:10.1051/0004-6361:20078027. Retrieved 2025-10-18.
  3. ^ 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.
  4. ^ "Kinematical Structure of the Magellanic System - R.P. van der Marel et al". ned.ipac.caltech.edu. Retrieved 2025-10-11.
  5. ^ Pietrzyński, G.; Graczyk, D.; Gieren, W.; Thompson, I. B.; Pilecki, B.; Udalski, A.; Soszyński, I.; Kozłowski, S.; Konorski, P.; Suchomska, K.; Bono, G.; Moroni, P. G. Prada; Villanova, S.; Nardetto, N.; Bresolin, F.; Kudritzki, R. P.; Storm, J.; Gallenne, A.; Smolec, R.; Minniti, D.; Kubiak, M.; Szymański, M. K.; Poleski, R.; Wyrzykowski, Ł.; Ulaczyk, K.; Pietrukowicz, P.; Górski, M.; Karczmarek, P. (2013). "An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent". Nature. 495 (7439): 76–79. arXiv:1303.2063. Bibcode:2013Natur.495...76P. doi:10.1038/nature11878. Retrieved 2025-10-18.
  6. ^ a b 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.
  7. ^ a b "Is the orbital period 8.15 h?". academic.oup.com. Retrieved 2025-10-18.
  8. ^ 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.
  9. ^ 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.
  10. ^ a b 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.
  11. ^ a b 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.
  12. ^ "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2025-10-08.
  13. ^ 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.
  14. ^ 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.
  15. ^ Pakull, M. (1979). "Probable optical identification of LMC X-2". The Messenger. 16: 38. Bibcode:1979Msngr..16...38P.
  16. ^ [1]
  17. ^ a b 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.
  18. ^ 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.
  19. ^ "LMC X-2". maxi.riken.jp. Retrieved 2025-10-11.
  20. ^ https://academic.oup.com/mnras/article/316/4/729/1084536
  21. ^ 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.
  22. ^ Lavagetto, G.; Iaria, R.; d'Ai, A.; Di Salvo, T.; Robba, N. R. (2008). "Spectral Analysis of LMC-X2 with XMM/Newton". Chinese Journal of Astronomy and Astrophysics Supplement. 8: 325. Bibcode:2008ChJAS...8..325L.
  23. ^ White, Nicholas E.; Smale, A. P.; Homan, J.; Kuulkers, E. (2003-01-30). The Complete Z-diagram of LMC X-2 (Report).
  24. ^ 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.
  25. ^ 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. arXiv:2007.05938. doi:10.1093/mnras/staa2063. ISSN 0035-8711.
This article is issued from Wikipedia. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.