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Title: X-RAY BINARIES IN THE ULTRAHIGH ENCOUNTER RATE GLOBULAR CLUSTER NGC 6388

Abstract

We report the results of a joint Chandra Hubble Space Telescope study of the X-ray binary (XRB) population in the massive, high-density globular cluster NGC 6388. NGC 6388 has one of the highest predicted XRB production rates of any Galactic cluster. We detected a large population of 61 Chandra sources within the half-mass radius with L{sub X} > 5 Multiplication-Sign 10{sup 30} erg s{sup -1}. From the X-ray colors, luminosities, (lack of) variability, and spectral fitting, we identify five as likely quiescent low-mass X-ray binaries. Due to the extremely crowded nature of the core of NGC 6388, finding optical identifications to Chandra sources is challenging. We have identified four blue, optically variable counterparts to spectrally hard X-ray sources, evidence that these are bright cataclysmic variables (CVs). One showed variability of 2 mag in V, indicative of a dwarf nova eruption. One other likely CV is identified by its X-ray spectrum (partial covering with high N{sub H}) and strong variability, making five likely CVs identified in this cluster. The relatively bright optical magnitudes of these sources put them in the same class as CV1 in M15 and the brightest CVs in 47 Tuc.

Authors:
; ;  [1];  [2];  [3];  [4];  [5]
  1. Department of Astronomy, Indiana University, 727 E. Third St., Bloomington, IN 47405 (United States)
  2. Ingenuity New Faculty, Department of Physics, University of Alberta, Edmonton, AB T6G 2G7 (Canada)
  3. Harvard College Observatory, 60 Garden St., MS-6, Cambridge, MA 02138 (United States)
  4. Department of Physics, University of Alberta, Edmonton, AB T6G 2G7 (Canada)
  5. Advanced Fuel Research, Inc., 87 Church Street, East Hartford, CT 06108 (United States)
Publication Date:
OSTI Identifier:
22092376
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 756; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; BINARY STARS; COSMIC X-RAY SOURCES; DENSITY; GAMMA ASTRONOMY; HARD X RADIATION; LUMINOSITY; MASS; NOVAE; SPACE; STAR CLUSTERS; TELESCOPES; X-RAY SPECTRA

Citation Formats

Maxwell, J. Edward, Lugger, Phyllis M., Cohn, Haldan N., Heinke, Craig O., Grindlay, Jonathan E., Budac, Sonia A., Drukier, Gordon A., and Bailyn, Charles D., E-mail: tmaxwell@astro.indiana.edu, E-mail: lugger@astro.indiana.edu, E-mail: cohn@astro.indiana.edu, E-mail: heinke@ualberta.ca, E-mail: josh@cfa.harvard.edu. X-RAY BINARIES IN THE ULTRAHIGH ENCOUNTER RATE GLOBULAR CLUSTER NGC 6388. United States: N. p., 2012. Web. doi:10.1088/0004-637X/756/2/147.
Maxwell, J. Edward, Lugger, Phyllis M., Cohn, Haldan N., Heinke, Craig O., Grindlay, Jonathan E., Budac, Sonia A., Drukier, Gordon A., & Bailyn, Charles D., E-mail: tmaxwell@astro.indiana.edu, E-mail: lugger@astro.indiana.edu, E-mail: cohn@astro.indiana.edu, E-mail: heinke@ualberta.ca, E-mail: josh@cfa.harvard.edu. X-RAY BINARIES IN THE ULTRAHIGH ENCOUNTER RATE GLOBULAR CLUSTER NGC 6388. United States. doi:10.1088/0004-637X/756/2/147.
Maxwell, J. Edward, Lugger, Phyllis M., Cohn, Haldan N., Heinke, Craig O., Grindlay, Jonathan E., Budac, Sonia A., Drukier, Gordon A., and Bailyn, Charles D., E-mail: tmaxwell@astro.indiana.edu, E-mail: lugger@astro.indiana.edu, E-mail: cohn@astro.indiana.edu, E-mail: heinke@ualberta.ca, E-mail: josh@cfa.harvard.edu. Mon . "X-RAY BINARIES IN THE ULTRAHIGH ENCOUNTER RATE GLOBULAR CLUSTER NGC 6388". United States. doi:10.1088/0004-637X/756/2/147.
@article{osti_22092376,
title = {X-RAY BINARIES IN THE ULTRAHIGH ENCOUNTER RATE GLOBULAR CLUSTER NGC 6388},
author = {Maxwell, J. Edward and Lugger, Phyllis M. and Cohn, Haldan N. and Heinke, Craig O. and Grindlay, Jonathan E. and Budac, Sonia A. and Drukier, Gordon A. and Bailyn, Charles D., E-mail: tmaxwell@astro.indiana.edu, E-mail: lugger@astro.indiana.edu, E-mail: cohn@astro.indiana.edu, E-mail: heinke@ualberta.ca, E-mail: josh@cfa.harvard.edu},
abstractNote = {We report the results of a joint Chandra Hubble Space Telescope study of the X-ray binary (XRB) population in the massive, high-density globular cluster NGC 6388. NGC 6388 has one of the highest predicted XRB production rates of any Galactic cluster. We detected a large population of 61 Chandra sources within the half-mass radius with L{sub X} > 5 Multiplication-Sign 10{sup 30} erg s{sup -1}. From the X-ray colors, luminosities, (lack of) variability, and spectral fitting, we identify five as likely quiescent low-mass X-ray binaries. Due to the extremely crowded nature of the core of NGC 6388, finding optical identifications to Chandra sources is challenging. We have identified four blue, optically variable counterparts to spectrally hard X-ray sources, evidence that these are bright cataclysmic variables (CVs). One showed variability of 2 mag in V, indicative of a dwarf nova eruption. One other likely CV is identified by its X-ray spectrum (partial covering with high N{sub H}) and strong variability, making five likely CVs identified in this cluster. The relatively bright optical magnitudes of these sources put them in the same class as CV1 in M15 and the brightest CVs in 47 Tuc.},
doi = {10.1088/0004-637X/756/2/147},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 756,
place = {United States},
year = {2012},
month = {9}
}