XMM-Newton X-ray sources in NGC 6553

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 M_{sun}_) and the best-fit temperature is kT_eff_=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 kT_eff_=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 ~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.