THE UNUSUAL X-RAY BINARIES OF THE GLOBULAR CLUSTER NGC 6652

Journal Article · Sun Jul 10 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/735/2/95· OSTI ID:21578409

Coomber, G; Heinke, C O ^[1]; Cohn, H N; Lugger, P M ^[2]

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1. Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton AB T6G 2G7 (Canada)
2. Department of Astronomy, Indiana University, 727 East 3rd St., Bloomington, IN 47405 (United States)

Our 5 ks Chandra ACIS-S observation of the globular cluster NGC 6652 detected seven X-ray sources, three of which were previously unidentified. This cluster hosts a well-known bright low-mass X-ray binary, source A (or XB 1832-330). Source B shows unusual rapid flaring variability, with an average L{sub X} (0.5-10 keV) {approx}2 x 10{sup 34} erg s{sup -1}, but with minutes-long flares up to L{sub X} = 9 x 10{sup 34} erg s{sup -1}. Its spectrum can be fit by an absorbed power law of photon index {Gamma} {approx} 1.24 and hardens as the count rate decreases. This suggests that part or all of the variation might be due to obscuration by the rim of a highly inclined accretion disk. Sources C and D, with L{sub X} {approx} 10{sup 33} erg s{sup -1}, have soft and unusual spectra. Source C requires a very soft component, with a spectrum peaking at 0.5 keV, which might be the hot polar cap of a magnetically accreting polar cataclysmic variable. Source D shows a soft spectrum (fit by a power law of photon index {approx}2.3) with marginal evidence for an emission line around 1 keV; its nature is unclear. The faint new sources E, F, and G have luminosities of 1-2 x 10{sup 32} erg s{sup -1}, if associated with the cluster (which is likely). E and F have relatively hard spectra (consistent with power laws with photon index {approx}1.5). G lacks soft photons, suggesting absorption with N{sub H} > 10{sup 22} cm{sup -2}.

• OSTI ID: 21578409
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 735; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BINARY STARS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ERUPTIVE VARIABLE STARS
NOVAE
STAR CLUSTERS
STARS
VARIABLE STARS