Understanding the LMXB X2127+119 in M 15: I. X-ray eclipses and dips

Zac Ioannou*, T. Naylor, A. P. Smale, P. A. Charles, K. Mukai

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


We present X-ray observations of the high-inclination low-mass X-ray binary system X2127+119 (AC211) in the globular cluster M 15 (NGC 7078). The observations consist of data acquired in 1996 with the RXTE satellite and in 1995 with the ASCA satellite. Also, the MPC1 data from the 1988 GINGA observations were de-archived and re-analysed. The phase-folded 2-10 keV hardness ratios from all three missions differ significantly indicating that the system can exhibit different spectral behaviours. We find that the X-ray eclipse profiles can be described relatively well using a simple model where the secondary star passes in front of a large X-ray emitting region. For this we require a mass ratio (q = M1/M2) of about one. The radius of this X-ray emitting region is ∼0.8 RL1 and its vertical extent ∼60° above the orbital plane. We suggest that if this X-ray emitting region were an optically thick corona, it would explain various puzzling aspects of this system. We also show that the X-ray dip observed at phases around 0.65 does not conform with the idea that the dip is caused by vertically extended material associated with the stream/disc impact region, but that it could be due to structure in the inner parts of the disc.

Original languageEnglish
Pages (from-to)130-140
Number of pages11
JournalAstronomy and Astrophysics
Issue number1
Publication statusPublished - 2002


  • Accretion, accretion discs
  • Stars: binaries: eclipsing, coronae
  • Stars: individual: X2127+119, AC211
  • X-rays: binaries

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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