Simulations of X-ray binaries

• Grant number: 23/15835-2
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: August 01, 2024
• End date: October 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Astronomy
• Principal Investigator: Rodrigo Nemmen da Silva
• Grantee: Pedro Naethe Motta
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

X-ray binaries (XRBs) undergo state transitions during which their spectral and timing properties change dramatically. The nature of these state transitions is a long-standing open question in black hole (BH) astrophysics. Moreover, the details of the hard state and how a colder thin accretion disk coexists with a much hotter corona are not well-understood. One leading idea is that they are associated with modulations in the mass accretion rate $\dot{M}$ which affect the amount of radiative cooling in the accretion flow. The goal of this project is to address the nature of hard and soft states and the transition from one to the other in XRBs, by performing global 3D GRMHD simulations of accretion flows around stellar mass BHs, incorporating our recent radiative cooling self-consistently in the dynamics through the bremsstrahlung, synchrotron and inverse Compton processes. We will use a state-of-the-art GPU-accelerated code to: (i) validate our cooling implementation; (ii) simulate two component flows consisting of a thin disk and a radiatively inefficient accretion flow, and measure the emergent properties of the system such as the truncation radius as a function of luminosity and BH spin; (iii) generate synthetic EM spectra from the simulations in a post-processing manner, and compare them with XRB observations. With this work, we will advance the understanding of accreting stellar mass black holes.