Accretion of material onto a black hole drags any magnetic fields present inwards, increasing their strength. Theory predicts that sufficiently strong magnetic fields can halt the accretion flow, producing a magnetically arrested disk (MAD). We analyze archival multi-wavelength observations of an outburst from the black hole X-ray binary MAXI J1820+070 in 2018. The radio and optical fluxes are delayed by about 8 and 17 days respectively, compared to the X-ray flux. We interpret this as evidence for the formation of a MAD. In this scenario, the magnetic field is amplified by an expanding corona, forming a MAD around the time of the radio peak. The optical delay is then due to thermal viscous instability in the outer disk.
@article{arxiv.2309.00200,
title = {Observations of a black hole X-ray binary indicate formation of a magnetically arrested disk},
author = {Bei You and Xinwu Cao and Zhen Yan and Jean-Marie Hameury and Bozena Czerny and Yue Wu and Tianyu Xia and Marek Sikora and Shuang-Nan Zhang and Pu Du and Piotr T. Zycki},
journal= {arXiv preprint arXiv:2309.00200},
year = {2023}
}
Comments
The author's version of the article which will appear in Science on 31 August 2023, 49 pages including the extended data. The online publication version can be found at https://doi.org/10.1126/science.abo4504