General-Relativistic Simulations of X-Ray Binary Accretion with Athena++ and AthenaK 1 views

We present general relativistic Monte Carlo radiative transfer calculations performed on radiation GRMHD simulations of stellar-mass black hole accretion flows generated with AthenaK. The simulations span sub-Eddington to super-Eddington accretion regimes and are post-processed to produce synthetic X-ray spectra. The resulting spectra exhibit the characteristic two-component structure observed in black hole X-ray binaries, consisting of a soft thermal disk component and a harder high-energy tail produced through inverse Compton scattering in a hot corona. Comparison across simulations with different density normalizations shows that increasing density significantly alters both the luminosity and spectral morphology of the system. Higher-density simulations produce higher accretion rates, leading to stronger hard X-ray emission and enhanced Comptonization, with the highest-accretion model displaying behavior consistent with a near- or super-Eddington accretion flow. Additional calculations show that high-accretion spectra are sensitive to assumptions about opacity in low-density funnel regions. The synthetic spectra were further characterized using multitemperature disk blackbody and power-law fitting models, which successfully reproduced the overall spectral structure. These results demonstrate the importance of radiation transport and coronal Comptonization in shaping the observable spectra of black hole accretion flows.

BS (Bachelor of Science)

simulation; black hole; x-ray binary; accretion, accretion disk; computational astrophysics

English

2026-05-11