Discovery of a candidate quiescent low-mass X-ray binary in the globular
  cluster NGC 6553
  This paper reports the search for quiescent low-mass X-ray binaries (qLMXBs)
in the globular cluster (GC) NGC 6553 using an XMM-Newton observation designed
specifically for that purpose. We spectrally identify one candidate qLMXB in
the core of the cluster, based on the consistency of the spectrum with a
neutron star H-atmosphere model at the distance of NGC 6553. Specifically, the
best-fit radius found using the three XMM European Photon Imaging Camera
spectra is R_NS=6.3(+2.3)(-0.8) km (for M_NS=1.4 Msun) and the best-fit
temperature is kTeff=136 (+21)(-34) eV. Both physical parameters are in
accordance with typical values of previously identified qLMXBs in GC and in the
field, i.e., R_NS~5-20 km and kTeff~50-150 eV. A power-law (PL) component with
a photon index Gamma=2.1(+0.5)(-0.8) is also required for the spectral fit and
contributes to ~33% of the total flux of the X-ray source. A detailed analysis
supports the hypothesis that the PL component originates from nearby sources in
the core, unresolved with XMM. The analysis of an archived Chandra observation
provides marginal additional support to the stated hypothesis. Finally, a
catalog of all the sources detected within the XMM field of view is presented
here.
