The 2018 outburst of MAXI J1820+070 as seen by Insight-HXMT

The 2018 outburst of MAXI J1820+070 as seen by Insight-HXMT
Ningyue Fan, Songyu Li, Rui Zhan, Honghui Liu, Zuobin Zhang, Cosimo Bambi, Long Ji, Xiang Ma, James F. Steiner, Shuang-Nan Zhang, Menglei Zhou
arXiv:2404.12161v1 Announce Type: new
Abstract: We present an analysis of the whole 2018 outburst of the black hole X-ray binary MAXI J1820+070 with Insight-HXMT data. We focus our study on the temporal evolution of the parameters of the source. We employ two different models to fit the thermal spectrum of the disk: the Newtonian model DISKBB and the relativistic model NKBB. These two models provide different pictures of the source in the soft state. With DISKBB, we find that the inner edge of the disk is close to the innermost stable circular orbit of a fast-rotating black hole and the corona changes geometry from the hard to the soft state, probably becoming compact and close to the black hole. With NKBB, we find that the disk is truncated in the soft state and that the coronal geometry does not change significantly during the whole outburst. However, we find that the model with NKBB can predict an untruncated disk around a fast-rotating black hole if we assume that the inclination angle of the disk is around 30 degrees (instead of 60 degrees, which is the inclination angle of the jet and is usually adopted as the inclination angle of the disk in the literature) and we employ a high-density reflection model. In such a case, we measure a high value of the black hole spin parameter with observations in the soft state, in agreement with the high spin value found from the analysis of the reflection features and in disagreement with the low spin value found by previous continuum-fitting method measurements with the inclination angle of the disk set to the value of the inclination angle of the jet.arXiv:2404.12161v1 Announce Type: new
Abstract: We present an analysis of the whole 2018 outburst of the black hole X-ray binary MAXI J1820+070 with Insight-HXMT data. We focus our study on the temporal evolution of the parameters of the source. We employ two different models to fit the thermal spectrum of the disk: the Newtonian model DISKBB and the relativistic model NKBB. These two models provide different pictures of the source in the soft state. With DISKBB, we find that the inner edge of the disk is close to the innermost stable circular orbit of a fast-rotating black hole and the corona changes geometry from the hard to the soft state, probably becoming compact and close to the black hole. With NKBB, we find that the disk is truncated in the soft state and that the coronal geometry does not change significantly during the whole outburst. However, we find that the model with NKBB can predict an untruncated disk around a fast-rotating black hole if we assume that the inclination angle of the disk is around 30 degrees (instead of 60 degrees, which is the inclination angle of the jet and is usually adopted as the inclination angle of the disk in the literature) and we employ a high-density reflection model. In such a case, we measure a high value of the black hole spin parameter with observations in the soft state, in agreement with the high spin value found from the analysis of the reflection features and in disagreement with the low spin value found by previous continuum-fitting method measurements with the inclination angle of the disk set to the value of the inclination angle of the jet.