From X-ray Binaries to Ultraluminous X-ray Sources: Evolution of Accretion Disks Across Different States with Relativistic and Non- Relativistic Disk Models

Abstrakt

M82 X-1 has been under the spotlight as a possible host for an intermediate-mass black hole (IMBH) due to its extremely luminous nature and observed frequencies of twin-peaked quasi-periodic oscillations. Previous spectral studies pointed towards much lower black hole mass values but obtaining better constraints on the black hole mass was greatly limited due to the complexity of the parameter space and the nature of the disk model adopted.

Our previous results using ~2000 RXTE observations of black hole X-ray binaries (BHXRBs) showed the importance of self-consistent modelling of the accretion disk to include the general relativistic effects on the observed spectrum due to strong gravitational potentials around black holes when measuring physical parameters of the system. To efficiently overcome any effects of local minima or complex degeneracies of individual parameters of the model, we employ the Bayesian X-ray Analysis (BXA) software to perform a global exploration of the parameter space and obtain a much better view of the important parameters using combined simultaneous Chandra + NuSTAR spectra of M82 X-1.

Employing relativistic accretion disk models that include the signatures of the physical properties of the black hole on the observed spectrum indicates that it's impossible to reproduce the observed spectral shape assuming an IMBH of >1000 M_sun and disk temperatures as high as 6 keV as previously reported do not correspond to physical values for accretion disks around black holes of any nature. The inverse scaling between the black hole mass and disk temperature implies much lower disk temperatures than of black hole X-ray binaries.

This places the IMBH accretor as an unlikely scenario even for super-Eddington accretion rates and our results provide strong support for a stellar-mass black hole accreting in an extreme regime. The observed L-T trend from M82 X-1 can be interpreted to correspond to a specific accretion state in numerous black hole X-ray binaries where significant deviations from the theoretical L-T relationship were observed.

Our previous results from the study of accretion disks in BHXRBs showed a dependency between the selection of the disk model and the slope of these specific observations. We will present the results from the spectral study of M82 X-1 and discuss the nature of the black hole in connection to observed properties of black hole X-ray binaries focusing on the implications of the relativistic and non-relativistic treatment of the accretion disk around the black hole of any nature on the measured properties of the system.