Insight-HXMT Views Her X-1: Probing the Dependence of the Cyclotron Line Energy on Flux and Time
oleh: G. C. Xiao, R. Staubert, L. Ji, M. Y. Ge, Q. Z. Liu, J. L. Qu, S. Zhang, S. N. Zhang, J. Z. Yan, J. Li, Q. C. Bu, Y. L. Tuo, H. X. Liu, Z. X. Yang
| Format: | Article |
|---|---|
| Diterbitkan: | IOP Publishing 2023-01-01 |
Deskripsi
Recent observations of Her X-1 with NuSTAR (as well as with INTEGRAL, Swift, and Astrosat) have provided evidence that the nearly 20 yr-long decay of the cyclotron line energy since ∼1994 has ended and that a stable value has replaced the decay. Using the observations of the Hard X-ray Modulation Telescope (Insight-HXMT) performed between 2017 July and 2020 February, we analyze the spectra of Her X-1 in its main-on state, focusing on tracing the evolution of cyclotron line energy. While our analysis of eight main-on observations with Insight-HXMT (two in coordination with NuSTAR) shows significant differences with the results of NuSTAR, two earlier findings are confirmed: the positive correlation between the cyclotron line energy and the X-ray flux (source luminosity) and the constancy of the flux-normalized cyclotron line energy during 2017–2020—albeit with significant uncertainty about the absolute value.