Accretion properties of MAXI J1813-095 during its failed outburst in 2018

Abstract

We present the results obtained from detailed timing and spectral studies of a black hole candidate MAXI J1813–095 using Swift, NICER, and NuSTAR observations during its 2018 outburst. The timing behavior of the source is mainly studied by examining NICER light curves in the 0.5–10 keV range. We did not find any signature of quasi-periodic oscillations in the power density spectra of the source. We carry out spectral analysis with a combined disk blackbody & power law model, and physical two-component advective flow (TCAF) model. From the combined disk blackbody & power-law model, we extracted thermal and non-thermal fluxes, photon index and inner disk temperature. We also find evidence for weak reflection in the spectra. We have tested the physical TCAF model on a broadband spectrum from NuSTAR and Swift/XRT. The parameters like mass accretion rates, the size of Compton clouds and the shock strength are extracted. Our result affirms that the source remained in the hard state during the entire outburst which indicates a 'failed' outburst. We estimate the mass of the black hole as 7.4 ± 1.5 M⊙ from the spectral study with the TCAF model. We apply the LAOR model for the Fe Kα line emission. From this, the spin parameter of the black hole is ascertained as a* > 0.76$ The inclination angle of the system is estimated to be in the range of 28° – 45° from the reflection model. We find the source distance to be ~ 6 kpc.