A relativistic iron emission line from the neutron star low-mass X-ray binary GX3+1

Piraino S;Santangelo A;Kaaret P;Mück B;D'AI', ANTONINO;Di Salvo T;Iaria R;Robba N;BURDERI, LUCIANO;Egron E.

2012-01-01

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Abstract

We present the results of a spectroscopic study of the Fe Ka 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 L-X similar to 10(37) erg s(-1). When fitted with a two-component model, the X-ray spectrum shows broad residuals at similar to 6-7 keV that can be ascribed to an iron Ka 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 similar to 25R(g) and a disk inclination of 35 degrees < i < 44 degrees. RI Iaria, Rosario/F-2520-2012; D'Ai, Antonino/B-3962-2012; Di Salvo, Tiziana/F-3973-2012