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

Journal Article · Mon Sep 10 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/756/2/147· OSTI ID:22092376

Maxwell, J. Edward; Lugger, Phyllis M.; Cohn, Haldan N. ^[1]; Heinke, Craig O. ^[2]; Grindlay, Jonathan E. ^[3]; Budac, Sonia A. ^[4]; Drukier, Gordon A. ^[5]

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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)

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.

• OSTI ID: 22092376
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 756; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTROPHYSICS
BINARY STARS
COSMIC X-RAY SOURCES
DENSITY
GAMMA ASTRONOMY
HARD X RADIATION
LUMINOSITY
MASS
NOVAE
SPACE
STAR CLUSTERS
TELESCOPES
X-RAY SPECTRA