A relativistic iron emission line from the neutron star low-mass X-ray binary GX 3+1

S. Piraino (1,2), A. Santangelo (2), P. Kaaret (3) , B. Mück (2), A. D’Aí (4), T. Di Salvo (4), R. Iaria (4), N. Robba (4), L. Burderi (5), and E. Egron (5) ((1) INAF-IASF di Palermo, via Ugo La Malfa 153, 90146 Palermo, Italy; (2) Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Sand 1, 72076 Tübingen, Germany; (3) Department of Physics and Astronomy University of Iowa, Iowa City, IA 52242 USA; (4) Dipartimento di Fisica, Universitá degli Studi di Palermo, via Archirafi, 90100 Palermo, Italy; (5) Dipartimento di Fisica, Universitá degli Studi di Cagliari, SP Monserrato-Sestu, KM 0.7, Monserrato, Italy)

We present the results of a spectroscopic study of the Fe Kα emission of the persistent neutron-star atoll low-mass X-ray binary and type I X-ray burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux modulation over several years and we observed it during its fainter phase, which corresponds to an X-ray luminosity of Lx~10^37 ergs/s. When fitted with a two-component model, the X-ray spectrum shows broad residuals at ~6-7 keV that can be ascribed to an iron Kα fluorescence line. In addition, lower energy features are observed at ~3.3 keV, ~3.9 keV and might originate from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a relativistically smeared profile. This result is robust against possible systematics caused by instrumental pile-up effects. Assuming that the line is produced by reflection from the inner accretion disk, we infer an inner disk radius of ~25 Rg and a disk inclination of 35º < i < 44º.

See complete preprint ===> http://arxiv.org/abs/1205.3348

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