Insight-HXMT observations of jet-like corona in a black hole X-ray binary MAXI J1820+070

TL;DR

This study analyzes the evolution of the corona in a black hole X-ray binary during an outburst, revealing a jet-like corona with increasing outflow velocity as it approaches the black hole, based on reflection fraction observations.

Contribution

It introduces a jet-like corona model explaining the decreasing reflection fraction through coronal outflow velocity changes during the outburst decay.

Findings

Reflection fraction decreases during decay phase.

Coronal material likely outflows faster as it nears the black hole.

Jet-like corona model explains observed phenomena.

Abstract

A black hole X-ray binary produces hard X-ray radiation from its corona and disk when the accreting matter heats up. During an outburst, the disk and corona co-evolves with each other. However, such an evolution is still unclear in both its geometry and dynamics. Here we report the unusual decrease of the reflection fraction in MAXI J1820+070, which is the ratio of the coronal intensity illuminating the disk to the coronal intensity reaching the observer, as the corona is observed to contrast during the decay phase. We postulate a jet-like corona model, in which the corona can be understood as a standing shock where the material flowing through. In this dynamical scenario, the decrease of the reflection fraction is a signature of the corona's bulk velocity. Our findings suggest that as the corona is observed to get closer to the black hole, the coronal material might be outflowing faster.