Discovery of oscillations above 200 keV in a black hole X-ray binary with Insight-HXMT

TL;DR

This paper reports the first detection of low-frequency quasi-periodic oscillations above 200 keV in a black hole X-ray binary, revealing new insights into the high-energy behavior of accretion flows and jet precession.

Contribution

It presents the discovery of LFQPOs above 200 keV in MAXI J1820+070, providing new observational evidence to test models of accretion and jet dynamics.

Findings

LFQPOs detected above 200 keV

Energy-dependent phase lag behavior observed

LFQPO likely linked to jet precession

Abstract

Low-frequency quasi-periodic oscillations (LFQPOs) are commonly found in black hole X-ray binaries, and their origin is still under debate. The properties of LFQPOs at high energies (above 30 keV) are closely related to the nature of the accretion flow in the innermost regions, and thus play a crucial role in critically testing various theoretical models. The Hard X-ray Modulation Telescope (Insight-HXMT) is capable of detecting emissions above 30 keV, and is therefore an ideal instrument to do so. Here we report the discovery of LFQPOs above 200 keV in the new black hole MAXI J1820+070 in the X-ray hard state, which allows us to understand the behaviours of LFQPOs at hundreds of kiloelectronvolts. The phase lag of the LFQPO is constant around zero below 30 keV, and becomes a soft lag (that is, the high-energy photons arrive first) above 30 keV. The soft lag gradually increases with energy and reaches ~0.9s in the 150-200 keV band. The detection at energies above 200 keV, the large soft lag and the energy-related behaviors of the LFQPO pose a great challenge for most currently existing models, but suggest that the LFQPO probably originates from the precession of a small-scale jet.