2018MNRAS.479.2834H -
Mon. Not. R. Astron. Soc., 479, 2834-2852 (2018/September-2)
A Deep X-ray Survey of the globular cluster Omega Centauri.
HENLEYWILLIS S., COOL A.M., HAGGARD D., HEINKE C., CALLANAN P. and ZHAO Y.
Abstract (from CDS):
We identify 233 X-ray sources, of which 95 are new, in a 222 ks exposure of Omega Centauri with the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer detector. The limiting unabsorbed flux in the core is fX(0.5-6.0 keV) ≃3 x 10–16 erg s–1 cm–2 (Lx ≃ 1 x 1030 erg s–1 at 5.2 kpc). We estimate that ∼60 ± 20 of these are cluster members, of which ∼30 lie within the core (rc = 155 arcsec), and another ∼30 between 1-2 core radii. We identify four new optical counterparts, for a total of 45 likely identifications. Probable cluster members include 18 cataclysmic variables (CVs) and CV candidates, one quiescent low-mass X-ray binary, four variable stars, and five stars that are either associated with ω Cen's anomalous red giant branch or are sub-subgiants. We estimate that the cluster contains 40 ± 10 CVs with Lx > 1031 erg s–1, confirming that CVs are underabundant in ω Cen relative to the field. Intrinsic absorption is required to fit X-ray spectra of six of the nine brightest CVs, suggesting magnetic CVs, or high-inclination systems. Though no radio millisecond pulsars (MSPs) are currently known in ω Cen, more than 30 unidentified sources have luminosities and X-ray colours like those of MSPs found in other globular clusters; these could be responsible for the Fermi-detected gamma-ray emission from the cluster. Finally, we identify a CH star as the counterpart to the second brightest X-ray source in the cluster and argue that it is a symbiotic star. This is the first such giant/white dwarf binary to be identified in a globular cluster.
Abstract Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
binaries: close - novae, cataclysmic variables - globular clusters: individual: o Centauri - NGC 5139 - X-rays: binaries
VizieR on-line data:
<Available at CDS (J/MNRAS/479/2834): table1.dat>
Nomenclature:
Table 1: [HCD2009] NNNa N=95 among (Nos 11d-113b) added.
Status at CDS
:
All or part of tables of objects will be ingested in SIMBAD with priority 1.
Simbad objects:
14
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