Iron fluorescence line as a tracer of reprocessing environment

Iron fluorescence emission is ubiquitous in HMXB systems. Iron fluorescence emission is ubiquitous in HMXB systems. The iron fluorescence is produced by reprocessed emission from the binary environment populated by the dense clumpy wind of the companion stars in the HMXB systems. A large collecting area and excellent sensitivity near the iron fluorescence band make XMM−Newton an ideal instrument for studying the phase variation of the reprocessing environment in these systems. We undertook a systematic study of several bright HMXB pulsars observed with XMM−Newton. Among these sources, GX 301-2, Vela X-1, and Cen X-3 were bright with long exposure and significant iron line equivalent width. I used these data sets to study the variations in iron emission with the spin phase of the NS at different orbital and super-orbital phases. The high collecting area and excellent spectral resolution of XMM-Newton not only allow us to distinguish the neutral and ionized iron emission lines but also allow us to perform a detailed study of the spin variation of these emission lines. Pulse-phase resolved analysis from all the sources shows significant variation of iron fluorescent emission with phase. We discuss the results from the observations. The pulsed nature of the fluorescence emission is not expected from a homogeneous and isotropic binary environment. In GX 301-2, clumpy winds can explain the observed variation of iron fluorescence.