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Title: 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 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,more » 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}.« less

Authors:
;  [1]; ;  [2];  [3]
  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)
  3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
21578409
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 735; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/735/2/95; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC X-RAY SOURCES; NOVAE; STAR CLUSTERS; BINARY STARS; COSMIC RAY SOURCES; ERUPTIVE VARIABLE STARS; STARS; VARIABLE STARS

Citation Formats

Coomber, G., Heinke, C. O., Cohn, H. N., Lugger, P. M., and Grindlay, J. E., E-mail: heinke@ualberta.ca. THE UNUSUAL X-RAY BINARIES OF THE GLOBULAR CLUSTER NGC 6652. United States: N. p., 2011. Web. doi:10.1088/0004-637X/735/2/95.
Coomber, G., Heinke, C. O., Cohn, H. N., Lugger, P. M., & Grindlay, J. E., E-mail: heinke@ualberta.ca. THE UNUSUAL X-RAY BINARIES OF THE GLOBULAR CLUSTER NGC 6652. United States. doi:10.1088/0004-637X/735/2/95.
Coomber, G., Heinke, C. O., Cohn, H. N., Lugger, P. M., and Grindlay, J. E., E-mail: heinke@ualberta.ca. Sun . "THE UNUSUAL X-RAY BINARIES OF THE GLOBULAR CLUSTER NGC 6652". United States. doi:10.1088/0004-637X/735/2/95.
@article{osti_21578409,
title = {THE UNUSUAL X-RAY BINARIES OF THE GLOBULAR CLUSTER NGC 6652},
author = {Coomber, G. and Heinke, C. O. and Cohn, H. N. and Lugger, P. M. and Grindlay, J. E., E-mail: heinke@ualberta.ca},
abstractNote = {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}.},
doi = {10.1088/0004-637X/735/2/95},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 735,
place = {United States},
year = {2011},
month = {7}
}