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

Abstract

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 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 on board 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.

Observation of GRB 221009A Early Afterglow in X-Ray/Gamma-Ray Energy Bands

“…In addition, the source spectrum can also be measured by Earth occultation analysis (Xue et al 2023). For Fermi/GBM, the Earth occultation started at ∼T 0 +1430 s and ended at ∼T 0 +1467 s, while it started at ∼T 0 +1810 s and ended at ∼T 0 +1860 s for GECAM-C.…”

The First JWST Spectrum of a GRB Afterglow: No Bright Supernova in Observations of the Brightest GRB of all Time, GRB 221009A

“…where E is the photon energy, R(E, E ch ) is the detector response, E ch is the energy channel, and τ (t, E) is the atmospheric optical depth along the line of sight. The calculation of τ (t, E) is the same as in Method26 , using the atmospheric model NRLMSIS-2.0 Method27 . To model the occultation data, we also assume that the background during the occultation is flat enough so that the background rate for each energy channel can be fit through b(t, ch) = e b 0 +b 1 t .…”

“…where D is the count recorded in channel E ch and time bin ∆t. The summation is over the 20-200 keV energy channels of the two GRDs and time bins with bin width of 0.5 s from T 0 + 1800 to T 0 + 1865 s. The data modeling method used here is quite similar to Method26 , but in this case our goal is to fit the parameters of the source.…”

Long-Term Density Trend in the Mesosphere and Lower Thermosphere from Occultations of the Crab Nebula with X-Ray Astronomy Satellites

“…The history of the dual usage of X-ray horizon crossing transitions is summarized in Wood et al (2020). Recently, Katsuda et al (2021), hereafter Paper I, and Yu et al (2022bYu et al ( , 2022a; Xue et al (2023) applied the same technique to derive atmospheric vertical density profiles, using Japanese and Chinese X-ray astronomy satellites, respectively. In this paper, we analyze atmospheric occultation data of the Crab Nebula acquired with X-ray astronomy satellites, ASCA, RXTE, Suzaku, NuSTAR, and Hitomi to reveal long-term trend of the neutral density in the MLT region.…”