Insight-HXMT, NuSTAR and INTEGRAL Data Show Disk Truncation in the Hard State of the Black-Hole X-Ray Binary MAXI J1820+070

TL;DR

This study combines data from HXMT, NuSTAR, and INTEGRAL to analyze the X-ray spectra of MAXI J1820+070, revealing disk truncation in the hard state and demonstrating the spectral complexity required for accurate modeling.

Contribution

The paper provides the first joint spectral analysis of MAXI J1820+070 using three satellites, confirming disk truncation at over 10 gravitational radii and highlighting the spectral complexity needed for fitting.

Findings

Spectra from HXMT, NuSTAR, and INTEGRAL are consistent.

Disk truncation occurs at >10 gravitational radii.

HXMT data alone cannot tightly constrain the inner disk radius.

Abstract

We study X-ray and soft gamma-ray spectra from the hard state of the accreting black-hole binary MAXI J1820+070. We perform analysis of joint spectra from HXMT, NuSTAR and INTEGRAL. We find an overall agreement between the spectra from all three satellites. Satisfactory fits to the data require substantial spectral complexity, with our models including two Comptonization regions and their associated disk reflection, a disk blackbody and a narrow Fe K$\alpha$ line. Our fits confirm the presence of the truncation of the reflecting optically-thick disk at least at $>$10 gravitational radii. However, we find that the HXMT data alone cannot significantly constrain the disk inner radii.