Low-frequency quasiperiodic 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 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 ~0.9 s in the 150–200 keV band. The detection at energies above 200 keV, the large soft lag and the energy-related behaviours of the LFQPO pose a great challenge for most existing models, but suggest that the LFQPO probably originates from the precession of a small-scale jet.

低频准周期振荡（LFQPO）通常在黑洞X射线双星中发现，其起源仍在争论中。LFQPO在高能量（30 keV以上）下的性质与最内层区域吸积流的性质密切相关，因此在严格测试各种理论模型中起着至关重要的作用。硬X射线调制望远镜能够检测30 keV以上的辐射，因此是实现此目的的理想仪器。在这里，我们报告了在新的黑洞MAXI J1820 + 070中在X射线硬态下发现了超过200 keV的LFQPO的发现，这使我们能够了解LFQPO在几百千伏的行为。LFQPO的相位滞后在30 keV以下恒定为零，并且在30 keV以上变为软滞后（即高能光子首先到达）。软滞后随能量逐渐增加，在150–200 keV频段达到〜0.9 s。对于大多数现有模型，在高于200 keV的能量下进行检测，较大的软滞后以及LFQPO的与能量有关的行为对大多数现有模型提出了巨大挑战，但建议LFQPO可能源自小型喷气机的岁差。