2019MNRAS.486..195S

Low-mass X-ray binaries (LMXBs) have a wide range of X-ray properties which can be utilized to reveal many physical conditions of the associated accretion discs. We use the spectral synthesis code CLOUDY to perform a detailed modelling of neutron star LMXBs GX 13+1, MXB 1659-298, 4U 1323-62, and XB 1916-053, and characterize the underlying physical conditions, such as density, radiation field, metallicity, wind velocity, etc. For this purpose we model highly ionized spectra of Fe, Ca, S, Si, Mg, Al in the soft X-ray band, and compare the predicted line flux ratios with the observed values. We also find that the strength and profile of these spectral lines get modified in the presence of magnetic field in the accretion disc. Using this, we estimate an upper limit of the existing magnetic field to be about a few hundred to a few thousand Gauss in the accretion discs of these four LMXBs.