A Deep Chandra Survey of the Globular Cluster 47 Tucanae: Catalog of Point Sources

2005

147 citations recorded by the source corpus.

We have detected 300 X-ray sources within the half-mass radius (2.′79) of the globular cluster 47 Tucanae in a deep (281 ks) Chandra exposure. We perform photometry and simple spectral fitting for our detected sources and construct luminosity functions, X-ray color-magnitude, and color-color diagrams. Eighty-seven X-ray sources show variability on timescales from hours to years. Thirty-one of the new X-ray sources are identified with chromospherically active binaries from the catalogs of Albrow and coworkers. The radial distributions of detected sources imply that roughly 70 are background sources of some kind. The radial distribution of the known millisecond pulsar (MSP) systems is consistent with that expected from mass segregation, if the average neutron star mass is 1.39 ± 0.19 M☉. Most source spectra are well fitted by thermal plasma models, except for quiescent low-mass X-ray binaries (qLMXBs; containing accreting neutron stars) and MSPs. We identify three new candidate qLMXBs with relatively low X-ray luminosities. One of the brightest cataclysmic variables (CVs; X10) shows evidence (a 4.7 hr period pulsation and strong soft X-ray emission) for a magnetically dominated accretion flow as in AM Her systems. Most of the bright CVs require intrinsic NH columns of order 1021 cm-2, suggesting a possible DQ Her nature. A group of X-ray sources associated with bright (sub)giant stars also requires intrinsic absorption. By comparing the X-ray colors, luminosities, variability, and quality of spectral fits of the detected MSPs to those of unidentified sources, we estimate that a total of ~25 MSPs exist in 47 Tuc (<60 at 95% confidence), regardless of their radio beaming fraction. We estimate that the total number of neutron stars in 47 Tuc is of order 300, reducing the discrepancy between theoretical neutron star retention rates and observed neutron star populations in globular clusters. Comprehensive tables of source properties and simple spectral fits are provided electronically.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a9d24f89faf6bf917b38b436d93c864db5bea704

Citations in the corpus

• A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope (2010, unknown): “Heinke et al. (2005) estimate that a total of ∼ 25 MSPs exist in 47 Tuc ( < 60 at 95% confidence), regardless of their radio beaming fraction, based on their deep Chandra X-ray observations of this cluster.”
• Short gamma-ray bursts from binary neutron star mergers in globular clusters (2005, unknown): “05), qLMXBs (∼1) and MSPs (∼10) per cluster, as derived from Chandra studies of (primarily) non-core-collapse but high-central-density cluster”
• INNOVATIONS IN THE ANALYSIS OF CHANDRA-ACIS OBSERVATIONS (2010, unknown): “47 Tucanae (Heinke et al. 2005), Terzan 1 (Cackett et al. 2006), Terzan 5 (Heinke et al. 2006), NGC 288 (Kong et al. 2006), M30=NGC 7099 (Lugger et al. 2007), NGC 6366 and M 55 (Bassa et al. 2008), G1 (Kong et al. 2009).”
• A Hydrogen Atmosphere Spectral Model Applied to the Neutron Star X7 in the Globular Cluster 47 Tucanae (2005, unknown): “…104; hereafter 47 Tuc) is especially ideal due to its close distance (4.85±0.18 kpc), low reddening (E(B−V) = 0.024± 0.004, Gratton et al. 2003), presence of two reasonably bright qLMXBs (X5 and X7; Heinke et al. 2003, hereafter HGL03), and deepChandra observations (300 ksec, Heinke et al. 2005).”
• Formation and evolution of compact binaries in globular clusters – II. Binaries with neutron stars (2007, unknown): “…radius (Camilo & Rasio 2005), but the radial distribution of most pulsars is exactly as expected for a population that is produced in or around the core (Grindlay et al. 2002; Heinke et al. 2005b), with the exception of a few, likely ejected, pulsars in M15 and NGC 6752 (e.g. Colpi et al. 2002).”