NuSTAR monitoring of MAXI J1348-630: evidence of high density disc reflection

TL;DR

This study analyzes NuSTAR observations of MAXI J1348-630, revealing that high-density disc reflection models better explain the spectra and suggest the presence of high-density accretion discs and high-velocity outflows.

Contribution

It demonstrates that high-density disc reflection models resolve iron abundance issues and provides evidence for high-density discs in a transient black hole binary.

Findings

High-density disc reflection models fit the spectra well.

Iron abundance is consistent with solar when using high-density models.

Evidence of a high-velocity outflow at 7.3 keV absorption lines.

Abstract

We present the broadband spectral analysis of all the six hard, intermediate and soft state NuSTAR observations of the recently discovered transient black hole X-ray binary MAXI J1348-630 during its first outburst in 2019. We first model the data with a combination of a multi-colour disc and a relativistic blurred reflection, and, whenever needed, a distant reflection. We find that this simple model scheme is inadequate in explaining the spectra, resulting in a very high iron abundance. We, therefore, explore the possibility of reflection from a high-density disc. We use two different sets of models to describe the high-density disc reflection: relxill-based reflection models, and reflionx-based ones. The reflionx-based high-density disc reflection models bring down the iron abundance to around the solar value, while the density is found to be $10^{20.3-21.4} \rm cm^{-3}$. We also find evidence of a high-velocity outflow in the form of $\sim$7.3 keV absorption lines. The consistency between the best-fit parameters for different epochs and the statistical significance of the corresponding model indicates the existence of high-density disc reflection in MAXI J1348-630.