Spectral Calculations of 3D Radiation Magnetohydrodynamic Simulations of Super-Eddington Accretion onto a Stellar-mass Black Hole
Year: 2024
Type: article
Abstract: We use the Athena++ Monte Carlo (MC) radiation transfer module to postprocess simulation snapshots from nonrelativistic Athena++ radiation magnetohydrodynamic (RMHD) simulations. These simulations were run using a gray (frequency-integrated) approach but were also restarted and ran with a multigroup approach that accounts for Compton scattering with a Kompaneets operator. These simulations produced moderately super-Eddington accretion rates onto a 6.62 M ⊙ black hole. Since we only achieve inflow equilibrium out to 20–25 gravitational radii, we focus on the hard X-ray emission. We provide a comparison between the MC and RMHD simulations, showing that the treatment of Compton scattering in the gray RMHD simulations underestimates the gas temperature in the funnel regions above and below the accretion disk. In contrast, the restarted multigroup snapshots provide a treatment for the radiation field that is more consistent with the MC calculations, and result in postprocessed spectra with harder X-ray emission compared to their gray snapshot counterparts. We characterize these MC postprocessed spectra using commonly employed phenomenological spectral fitting models. We also attempt to fit our MC spectra directly to observations of the ultraluminous X-ray source (ULX) NGC 1313 X-1, finding best-fit values that are competitive to phenomenological model fits, indicating that first principle models of super-Eddington accretion may adequately explain the observed hard X-ray spectra in some ULX sources.
Source: The Astrophysical Journal
Institutions: University of Virginia, University of Southampton
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Aeronautics and Space Administration, University of Virginia, Dell EMC, Jefferson Scholars Foundation, Flatiron Health, Nuclear Safety and Security Commission, Ames Research Center, Engineering and Physical Sciences Research Council, Science and Technology Facilities Council, Astrophysics Division
Awards: G1259507762, OBSERVATIONS OF ACCRETION IN BLACK HOLE CANDIDATE X-RAY BINARIES AND ULTRALUMINOUS X-RAY SOURCES HAVE REACHED A POINT WHERE THEY ARE CAPABLE OF PROVIDING TIGHT CONSTRAINTS ON THE PROPERTIES OF THE ACCRETION FLOWS AND THE BLACK HOLE SPACETIMES IN WHICH THEY RESIDE. AT THIS POINT A PRIMARY LIMITATION IS THE QUALITY OF THE MODELS USED TO INTERPRET THE DATA. IN ORDER TO PROVIDE BETTER FIRST-PRINCIPLES MODELS WE PROPOSE TO EXTEND THE CAPABILITIES OF OUR RADIATION HYDRODYNAMICS CODE TO INCLUDE MONTE CARLO BASED RADIATION TRANSFER METHODS. THIS EXTENSION WILL ALLOW US TO BETTER CAPTURE THE FREQUENCY DEPENDENT ASPECTS OF THE RADIATIVE TRANSFER PROBLEMS IN OUR SIMULATIONS AND TO PROVIDE DETAILED SIMULATION BASED PREDICTIONS OF THE SPECTRUM VARIABILITY AND POLARIZATION OF BLACK HOLE ACCRETION FLOWS. WE HAVE ALREADY DEVELOPED STATE-OF-THE-ART RADIATION TRANSFER ALGORITHMS FOR SOLVING THE ANGLE DEPENDENT TRANSFER IN THE GENERAL RELATIVISTIC MAGNETOHYDRODYNAMIC CODE: ATHENA++. THESE RADIATION TRANSFER METHODS ALLOW US TO COMPUTE THE RADIATION FORCES HEATING AND COOLING SOURCE TERMS IN SIMULATIONS OF ACCRETION FLOWS. THE METHODS HAVE ALREADY BEEN IMPLEMENTED IN A SPECIAL RELATIVISTIC APPROACH AND WE ARE IN THE PROCESS OF EXTENDING THE RADIATION TRANSFER TO FULLY GENERAL RELATIVISTIC ALGORITHMS. THE RADIATION TRANSFER IS SOLVED IN THE SIMULATIONS USING A GRAY (FREQUENCY AVERAGED) CONSERVATIVE FINITE DIFFERENCE SCHEME. THIS APPROACH DOES NOT PROVIDE US WITH THE FREQUENCY DEPENDENT INFORMATION REQUIRED TO MAKE DETAILED SPECTRAL PREDICTIONS. THEREFORE WE PROPOSED TO DEVELOP A MONTE CARLO BASED ALGORITHM FOR SOLVING THE FREQUENCY DEPENDENT RADIATION TRANSFER EQUATION ON HYDRODYNAMICS SIMULATION GRID. IN THE FIRST STAGE OF THE PROJECT WE WILL INTEGRATE AND THE PIS EXISTING MONTE CARLO CODE INTO ATHENA ++ AND USE IT TO COMPUTE STEADY STATE SPECTRA FROM SNAPSHOTS OF TIME DEPENDENT SIMULATIONS. NEXT WE WILL EXTEND THE MODULE TO RUN IN CONCERT WITH THE SIMULATIONS TO PROVIDE TIME-DEPENDENT SPECTRAL PREDICTIONS. FINALLY WE WILL COUPLE OUR MONTE CARLO TRANSFER SCHEME DIRECTLY WITH THE HYDRODYNAMICS. WE WILL IMPLEMENT BOTH A MONTE CARLO ONLY FRAMEWORK AS WELL AS A HYBRID FRAMEWORK THAT COUPLES THE MONTE CARLO SOLVER TO A CONSERVATIVE FINITE DIFFERENCE INTEGRATOR OF THE RELATIVISTIC STRESS-ENERGY TENSOR IN BLACK HOLE SPACETIMES. THE PRIMARY GOALS OF THIS PROPOSAL ARE TO IMPROVE THE SIMULATIONS BY BETTER MODELING THE FREQUENCY DEPENDENT PROPERTIES OF THE RADIATION AND TO GENERATE DETAILED SPECTRAL PREDICTIONS. THE FIRST GOAL IS PARTICULARLY IMPORTANT FOR ACCURATELY MODELING THE HEATING AND COOLING EFFECTS DUE TO COMPTON SCATTERING WHICH CAN DEPEND SENSITIVELY ON THE LOCAL RADIATION SPECTRUM. THE SECOND GOAL ALLOWS US TO CONSTRUCT SOPHISTICATED SYNTHETIC SPECTRA WHICH CAN BE DIRECTLY COMPARED WITH DATA. WE WILL CREATE SIMULATED OBSERVATIONS USING THESE OUTPUTS AND ANALYZE THEM USING STANDARD SPECTRAL ANALYSIS SOFTWARE AND TECHNIQUES (E.G. XSPEC). THE RESULTS OF THIS ANALYSIS WILL AID IN INTERPRETING THE RESULTS FROM OBSERVATIONS WITH CURRENT AND FORMER X-RAY SATELLITES SUCH AS CHANDRA SWIFT NUSTAR XMM-NEWTON SUZAKU AS WELL AS FUTURE NASA MISSIONS SUCH AS IXPE AND XARM., G1525616127, G1541806023, G1771230537, G2073976794, G2076157637, G2240879383, G2747059265, G3403823835, G3680780005, G3718830055, G4022262583, G581313191, G5997058474, G6537386148, G6873874887, G6926846737, G6955735330, Cambridge Service for Data Driven Discovery (CSD3) - A National Data Intensive Science Cloud for Converged Simulation, AI & Analytics, G7108246583, G7447190122, G7573294876, G7615445472, G7629755209, G7702914472, G7937591081, G8150249736, G8199619472, G8695159654, G878803593, G8958450467
OpenAlex ID: W4403311380