PROJECTS

Research project no. 59/2021 „The study of physical processes responsible for X-ray emission originating from accretion on neutron stars”  („The Excellence Initiative-Research University” programme, Polish acronym IDUB); implementation period: 01.07.2022-30.06.2024; head – Michał Szanecki, PhD.

X-ray radiation generated in the accretion is currently the subject of intensive research as a source of important information which are crucial in understanding of the physics of a strong gravitational field. An important analysis tool in such studies is a model which is used to estimate limits for various parameters of the system. The most important of them, such as spin, size of the central object or observational inclination, result from the properties of relativistic spectra of photons reflected from the surface of the accretion disk. While the currently available family of models computing such spectra for black holes is rich, there are no dedicated relativistic reflection models for neutron stars. 
 

The aim of the project was to implement a new, relativistic model of X-ray radiation observed from neutron star systems and apply it to three low-mass binary star systems: 4U1608-52, 4U1702-429 and 4U1728-34,to determine the basic physical parameters of these systems.  Obtaining a high degree of agreement between the spectrum generated by the model with data will enable comparison of the obtained results with current research outcomes for these objects, but also will provide a basis for a better understanding of the physics of accretion onto objects with a rigid surface and ultimately may help in determination of the equations of state of neutron matter.

The current development version of the model (reflkerr_ns) is publicly available on the University of Lodz website at: www.wfis.uni.lodz.pl/reflkerr and is ready for use with commonly used X-ray data analysis environments: XSPEC (https://heasarc.gsfc.nasa.gov/xanadu/xspec/) and ISIS (https://space.mit.edu/cxc/isis/).

The model is being intensively developed. Relatively new research on the effect of returning radiation (see the work of the authors: Riaz, S., Szanecki M., Niedźwiecki A. et al., "Impact of the Returning Radiation on the Analysis of the Reflection Spectra of Black Holes", The Astrophysical Journal 910, P 49 (2021)), indicate the need to take into account significant corrections of the second-order relativistic reflection (reflection of reflection), which, due to the complexity of reflection in systems with neutron stars, require a significant number of additional and time-consuming calculations.