Insight-HXMT Views Her X-1: Probing the Dependence of the Cyclotron Line Energy on Flux and Time
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2024
- DOI:
- 10.3847/1538-4357/acf9a6
- Bibcode:
- 2024ApJ...960...57X
- Keywords:
-
- Accretion;
- X-ray binary stars;
- 14;
- 1811