DISCOVERY OF A CANDIDATE QUIESCENT LOW-MASS X-RAY BINARY IN THE GLOBULAR CLUSTER NGC 6553
- Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A-2T8 (Canada)
- Department of Physics and Astronomy, Michigan State University, 3250 Biomedical Physical Science Building, East Lansing, MI 48824-2320 (United States)
- Department of Physics and Astronomy, Pennsylvania State University, 512 Davey Lab, University Park, PA 16802 (United States)
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{sub NS} = 6.3{sub -}0{sub .8}{sup +2.3} km (for M{sub NS} = 1.4 M{sub sun}) and the best-fit temperature is kT{sub eff} = 136{sub -34}{sup +21} eV. Both physical parameters are in accordance with typical values of previously identified qLMXBs in GC and in the field, i.e., R{sub NS} {approx} 5-20 km and kT{sub eff} {approx} 50-150 eV. A power-law (PL) component with a photon index {Gamma} = 2.1{sup +0.5}{sub -0.8} is also required for the spectral fit and contributes {approx}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.
- OSTI ID:
- 21584903
- Journal Information:
- Astrophysical Journal, Vol. 738, Issue 2; Other Information: DOI: 10.1088/0004-637X/738/2/129; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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