High-Resolution X-ray Imaging of a Globular Cluster Core: Compact Binaries in 47Tuc

• Published in: Science (American Association for the Advancement of Science) 2001-06, Vol.292 (5525), p.2290-2295
• Main Authors: Grindlay, Jonathan E., Heinke, Craig, Edmonds, Peter D., Murray, Stephen S.
• Format: Article
• Language: English
• Subjects: Astronomical observations; Astronomy; Astrophysics; Binary and multiple stars; Black holes; Braking radiation; Clusters; Colors; Earth, ocean, space; Evolution; Evolution (Biology); Exact sciences and technology; Fundamental astronomy and astrophysics. Instrumentation, techniques, and astronomical observations; Globular clusters in the milky way; Globular star clusters; Hemic system; Luminosity; Milky Way; Optical bursts; Power laws; Scientific Concepts; Star clusters; Stars; Stars & galaxies; Stellar clusters and associations; Stellar systems. Galactic and extragalactic objects and systems. The universe; X ray sources; X ray spectrum; X-ray; X-ray binaries; X-rays
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1061135

We have obtained high-resolution (≲1″) deep x-ray images of the globular cluster 47Tucanae (NGC 104) with the Chandra X-ray Observatory to study the population of compact binaries in the high stellar density core. A 70-kilosecond exposure of the cluster reveals a centrally concentrated population of faint (Lx∼ 1030-33ergs per second) x-ray sources, with at least 108 located within the central 2′ x 2.5′ and ≳ half with Lx≲ 1030.5ergs per second. All 15 millisecond pulsars (MSPs) recently located precisely by radio observations are identified, though 2 are unresolved by Chandra. The x-ray spectral and temporal characteristics, as well as initial optical identifications with the Hubble Space Telescope, suggest that ≳50 percent are MSPs, about 30 percent are accreting white dwarfs, about 15 percent are main-sequence binaries in flare outbursts, and only two to three are quiescent low-mass x-ray binaries containing neutron stars, the conventional progenitors of MSPs. An upper limit of about 470 times the mass of the sun is derived for the mass of an accreting central black hole in the cluster. These observations provide the first x-ray "color-magnitude" diagram for a globular cluster and census of its compact object and binary population.