Study of the reflection spectrum of the accreting neutron star GX 3+1 using XMM-Newton and INTEGRAL

Abstract

Broad emission features of abundant chemical elements, such as iron, are commonly seen in the X-ray spectra of accreting compact objects and their studies can provide useful information about the geometry of the accretion processes. In this work, we focus our attention on GX 3+1, a bright, persistent accreting low-mass X-ray binary, classified as an atoll source. Its spectrum is well described by an accretion disc plus a stable Comptonizing, optically thick corona which dominates the X-ray emission in the 0.3-20 keV energy band. In addition, four broad emission lines are found and we associate them with reflection of hard photons from the inner regions of the accretion disc, where Doppler and relativistic effects are important. We used self-consistent reflection models to fit the spectra of the 2010 XMM-Newton observation and the stacking of the whole data sets of 2010 INTEGRAL observations. We conclude that the spectra are consistent with reflection produced at ~10 gravitational radii by an accretion disc with an ionization parameter of ξ~ 600 erg cm s^-1 and viewed under an inclination angle of the system of ~35°. Furthermore, we detected for the first time for GX 3+1, the presence of a power-law component dominant at energies higher than 20 keV, possibly associated with an optically thin component of non-thermal electrons.