Detailed analysis on the reflection component for the black hole candidate MAXI J1348-630

TL;DR

This study performs a detailed spectral analysis of MAXI J1348-630 using NuSTAR data, focusing on reflection features to determine black hole spin, disk inclination, and state-dependent disk truncation.

Contribution

It provides the first comprehensive reflection-based measurement of the black hole spin and disk inclination for MAXI J1348-630 across its outburst states.

Findings

Black hole spin parameter a* ≈ 0.78

Disk inclination angle ≈ 29.2 degrees

Disk truncation observed in the hard state

Abstract

The black hole candidate MAXI J1348-630 was discovered on January 26th, 2019, with the Gas Slit Camera (GSC) on-board \textit{MAXI}. We report a detailed spectral analysis of this source by using the archived data of \textit{NuSTAR}. A total of 9 observations covered the complete outburst evolution of MAXI J1348-630 from the hard state to the soft state and finally back to the hard state. Additionally, the intermediate state is found in the transition from the hard state to the soft state. We use the state-of-art reflection model \verb'relxill' family to fit all the 9 spectra, and the spectra from two focal plane module detectors of \textit{NuSTAR} are jointly fitted for each observation. In particular, we concentrate on the results of the black hole spin parameter and the inclination of the accretion disk. Based on the analysis of the inner radius of the accretion disk, we obtain the spin parameter $a_* =0.78_{-0.04}^{+0.04}$, and the inclination angle of the inner disk $i = 29.2_{-0.5}^{+0.3}$ degrees. Furthermore, we also find that when the black hole is in the hard state, the accretion disk would show a significant truncation. The high iron abundance and ionization of the accretion disk obtained in the fitting results can be possibly explained by the high density of the accretion disk.