The Evolution of the Broadband Temporal Features Observed in the Black-hole Transient MAXI J1820+070 with Insight-HXMT

• Published in: The Astrophysical journal 2020-06, Vol.896 (1), p.33
• Main Authors: Ji, Long, Zhang, S. N., Méndez, Mariano, Qu, J. L., Maggi, Pierre, Zhang, S., Altamirano, Diego, Zhang, L., Ma, X., Lu, F. J., Li, T. P., Huang, Y., Zheng, S. J., Chen, Y. P., Chang, Z., Tuo, Y. L., Güngör, C., Song, L. M., Cao, X. L., Chen, Y., Liu, C. Z., Bu, Q. C., Cai, C., Chen, G., Chen, L., Chen, T. X., Chen, Y. B., Cui, W. W., Dong, Y. W., Gao, H., Gao, M., Gu, Y. D., Guan, J., Guo, C. C., Han, D. W., Huo, J., Jia, S. M., Jiang, L. H., Jiang, W. C., Jin, Y. J., Kong, L. D., Li, B., Li, G., Li, M. S., Li, W., Li, X., Li, X. B., Li, X. F., Li, Z. W., Liang, X. H., Liao, J. Y., Liu, G. Q., Liu, X. J., Liu, Y. N., Lu, B., Lu, X. F., Luo, Q., Luo, T., Meng, B., Nang, Y., Nie, J. Y., Ou, G., Sai, N., Shang, R. C., Song, X. Y., Wang, G. F., Wang, J., Wang, W. S., Wang, Y. D., Wang, Y. S., Wen, X. Y., Wu, B. B., Wu, B. Y., Wu, M., Xiao, G. C., Xiong, S. L., Yang, J. W., Yang, Y. J., Yi, Q. B., You, Y., Zhang, A. M., Zhang, C. M., Zhang, F., Zhang, J., Zhang, T., Zhang, W. C., Zhang, W., Zhang, W. Z., Zhang, Y., Zhang, Y. F., Zhang, Z., Zhang, Z. L., Zhao, H. S., Zhao, X. F., Zhou, D. K., Zhou, J. F., Zhuang, R. L., Zhu, Y., Wang, Lingjun
• Format: Article
• Language: English
• Subjects: Astrophysics; Black holes; Broadband; Compact objects; Energy bands; Evolution; Frequency ranges; Low-mass x-ray binary stars; Photons; Time dependence; Time lag
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab8db4

We study the evolution of the temporal properties of MAXI J1820+070 during the 2018 outburst in its hard state from MJD 58,190 to 58,289 with Insight-HXMT in a broad energy band 1-150 keV. We find different behaviors of the hardness ratio, the fractional rms and time lag before and after MJD 58,257, suggesting a transition occurred around this point. The observed time lags between the soft photons in the 1-5 keV band and the hard photons in higher energy bands, up to 150 keV, are frequency-dependent: the time lags in the low-frequency range, 2-10 mHz, are both soft and hard lags with a timescale of dozens of seconds but without a clear trend along the outburst; the time lags in the high-frequency range, 1-10 Hz, are only hard lags with a timescale of tens of milliseconds; they first increase until around MJD 58,257 and decrease after this date. The high-frequency time lags are significantly correlated to the photon index derived from the fit to the quasi-simultaneous NICER spectrum in the 1-10 keV band. This result is qualitatively consistent with a model in which the high-frequency time lags are produced by Comptonization in a jet.