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arXiv · 2502.14508

A possible overall scenario for the outburst evolution of MAXI J1820+070 revealed by Insight-HXMT

J. Q. Peng·S. Zhang·Y. P. Chen·L. D. Kong·P. J. Wang·S. N. Zhang·L. Ji·L. Tao·J. L. Qu·M. Y. Ge·Q. C. Shui·J. Li·Z. Chang·Z. S. Li·Y. X. Xiao
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Abstract

We study the spectral and temporal properties of the black hole X-ray transient binary MAXI J1820+070 during the 2018 outburst with Insight-HXMT observations. The outburst of MAXI J1820+070 can be divided into three intervals. For the two intervals of the outburst, we find that low-energy (below 140 keV) photos lag high-energy (140-170 keV) ones, while in the decay of the outburst, high-energy photons lag low-energy photons, both with a time scale of the order of days. Based on these results, the canonical hysteresis effect of the 'q' shape in the hardness-intensity diagram can be reformed into a roughly linear shape by taking into account the lag corrections between different energy bands. Time analysis shows that the high-frequency break of hard X-rays, derived from the power density spectrum of the first interval of the outburst is, in general, larger and more variable than that of soft X-rays. The spectral fitting shows that the coverage fraction of the hard X-rays drops sharply at the beginning of the outburst to around 0.5, then increases slightly. The coverage fraction drops to roughly zero once the source steps into a soft state and increases gradually to unity when the source returns to a low hard state. We discuss the possible overall evolution scenario of corona hinted from these discoveries.

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J. Q. Peng, S. Zhang, Y. P. Chen, L. D. Kong, P. J. Wang, S. N. Zhang, L. Ji, L. Tao, J. L. Qu, M. Y. Ge, Q. C. Shui, J. Li, Z. Chang, Z. S. Li, Y. X. Xiao. 2025-02-20. A possible overall scenario for the outburst evolution of MAXI J1820+070 revealed by Insight-HXMT. https://doi.org/10.1093/mnras%2Fstac3238

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