Pre-submission Thesis Presentation

Accreting X-ray pulsars (XRPs) are some of the brightest X-ray sources in the sky with widely varying intensities up to a few hundred mCrab. They are strongly magnetized spinning neutron stars that emit X-ray beams and are powered by matter from a binary companion. Various timing and spectroscopic studies performed on the X-ray photons received from them have been successful in revealing their emission characteristics, characteristics of the binary environment and the evolution of their orbits. The whole XRP environment could be broadly viewed as three different regions; the NS vicinity, the accretion disk and the binary environment. In the first part of the talk, I will discuss the timing and spectral studies we performed to understand some characteristics of these three regions in some of the XRPs. The spectroscopic studies involve the search for the spectral feature named ‘10 keV feature’ which is thought to originate near the NS poles, and probing the short-term evolution of the circum-binary environment of GX 301-2 by exploring the re-processed X-rays. The timing studies comprise understanding the energy dependence of QPOs in several XRPs that originate in their accretion disk, the temperature structure of the accretion disk corona in 4U 1822-371, and the long-term evolution of binary orbit of GX 301-2. Apart from the timing and spectroscopy windows, the third observational window that has the potential to understand the characteristics of XRPs is X-ray polarimetry. In the second part of the talk, I will discuss some aspects of the development of the Thomson scattering X-ray polarimetry instrument POLIX, which will fly onboard the upcoming India’s dedicated astronomy satellite mission of ISRO called X-ray Polarimetry Satellite (XPoSat). In particular, I will discuss the principle of operation of the instrument and some details of fabrication and tests performed on the Qualification model gas-filled proportional counter detector units of POLIX.