The Unusual X-ray Binaries of the Globular Cluster NGC 6652

Abstract

Our 5 ks Chandra ACIS-S observation of the globular cluster NGC 6652 detected 7 X-ray sources, 3 of which are 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_X(0.5-10 keV) ~2*10^{34} ergs/s, but with minutes-long flares up to L_X=9*10^{34} ergs/s. Its spectrum can be fit by an absorbed power-law of photon index Gamma~1.24, and hardens as the countrate 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_X ~10^{33} ergs/s, 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 ~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*10^{32} ergs/s, if associated with the cluster (which is likely). E and F have relatively hard spectra (consistent with power-laws with photon index ~1.5). G lacks soft photons, suggesting absorption with N_H>10^{22} cm^{-2}.

ApJ, in press. 9 pages, 9 figures (3 in color)

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Cited by in corpus (8)

• On the Origin of Sub-subgiant Stars. I. Demographics
• UltraCompCAT: a comprehensive Catalogue of Ultra-Compact and Short Orbital Period X-ray Binaries
• Searching for variable stars in the cores of five metal rich globular clusters using EMCCD observations
• An Examination of the X-ray Sources in the Globular Cluster NGC 6652
• A 2.15 Hour Orbital Period for the Low Mass X-Ray Binary XB 1832-330 in the Globular Cluster NGC 6652
• The MAVERIC Survey: Simultaneous Chandra and VLA observations of the transitional millisecond pulsar candidate NGC 6652B
• Multiwavelength evidence for a new flare-mode transitional millisecond pulsar
• New variable stars in NGC 6652 and its background Sagittarius stream