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

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.

9 pages,10 figures. Published in MNRAS

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Cited by in corpus (5)

• The nature of an imaginary quasi-periodic oscillation in the soft-to-hard transition of MAXI J1820+070
• Back to business: SLX 1746--331 after 13 years of silence
• The 2018 outburst of MAXI J1820+070 as seen by Insight-HXMT
• The origin of long soft lags and the nature of the hard-intermediate state in black hole binaries
• Multi-band power color-color diagrams of three black hole X-ray binaries observed with Insight-HXMT