Neutral Atmospheric Density Measurement Using Insight-HXMT Data by Earth Occultation Technique

Wang-Chen Xue, Xiao-Bo Li, Shao-Lin Xiong, Yong Chen, Shuang-Nan Zhang, Li-Ming Song, Shu Zhang, Ming-Yu Ge, You-Li Tuo, Hai-Tao Li, Dao-Chun Yu, Dong-Ya Guo, Jia-Cong Liu, Yan-Qiu Zhang, Chao Zheng

Submitted on 1 November 2022


The Earth occultation technique has broad applications in both astronomy and atmospheric density measurements. We construct the background model during the occultation of the Crab Nebula observed by the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) at energies between 6 keV and 100 keV. We propose a Bayesian atmospheric density retrieval method based on the Earth occultation technique, combining Poisson and Gaussian statistics. By modeling the atmospheric attenuation of X-ray photons during the occultation, we simultaneously retrieved the neutral densities of the atmosphere at different altitude ranges. Our method considers the correlation of densities between neighboring atmospheric layers and reduces the potential systematic bias to which previous work may be subject. Previous analyses based on light curve fitting or spectral fitting also lost some spectral or temporal information of the data. In contrast to previous work, the occultation data observed by the three telescopes onboard Insight-HXMT is fully used in our analysis, further reducing the statistical error in density retrieval. We apply our method to cross-check the (semi-)empirical atmospheric models, using 115 sets of occultation data of the Crab Nebula observed by Insight-HXMT. We find that the retrieved neutral density is ~10%, ~20%, and ~25% less than the values of the widely used atmospheric model NRLMSISE-00, in the altitude range of 55--80 km, 80--90 km, and 90--100 km, respectively. We also show that the newly released atmospheric model NRLMSIS 2.0 is generally consistent with our density measurements.


Comment: 20 pages, 12 figures, accepted for publication in ApJS

Subjects: Astrophysics - Instrumentation and Methods for Astrophysics; Astrophysics - High Energy Astrophysical Phenomena


Earth occultation of celestial source. The source appear to set (or rise) behind the limb of Earth, due to the satellite motion. The X-ray emission from source will be occulted when the LoS pass through the atmosphere or Earth.