Using collimated CZTI as all-sky X-ray detector based on Earth occultation technique

Singhal, A.; Srinivasan, Rahul; Bhalerao, V.; Bhattacharya, Dipankar; Rao, A. R.; Vadawale, S.

doi:10.1007/s12036-021-09743-1

Cited by 8 publications

(6 citation statements)

References 15 publications

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“…An older version of AstroSat CZTI mass model with minor differences has been successfully used to study the polarisation of prompt emission in several GRBs (Rao et al 2016;Chattopadhyay et al 2019;Chand et al 2019). Singhal et al (2021) used the same older version to measure fluxes of bright sources by the earth occultation technique. (Chattopadhyay et al 2021) demonstrated the validity of the mass model simulations for spectroscopic analyses, using this current mass model version.…”

Section: Discussionmentioning

confidence: 99%

“…When CZTI did not detect GW170817, we inferred that the source was occulted by the Earth-narrowing down the source localisation by a factor of two (Kasliwal et al 2017). The off-axis sensitivity of CZTI has also been leveraged for Earth-occultation studies of sources (Singhal et al 2021). Compton scattering within the CZT detectors is sensitive to polarisation of incoming photons, and has been successfully used to measure polarisation of GRBs (Chand et al 2019;Chattopadhyay et al 2019) and the Crab pulsar (Vadawale et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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The AstroSat mass model: Imaging and flux studies of off-axis sources with CZTI

et al. 2021

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The Cadmium Zinc Telluride Imager (CZTI) on AstroSat is a hard X-ray coded-aperture mask instrument with a primary field-of-view of 4:6 Â 4:6 (FWHM). The instrument collimators become increasingly transparent at energies above $ 100 keV, making CZTI sensitive to radiation from the entire sky. While this has enabled CZTI to detect a large number of off-axis transient sources, calculating the source flux or spectrum requires knowledge of the direction and energy dependent attenuation of the radiation incident upon the detector. Here, we present a GEANT4-based mass model of CZTI and AstroSat that can be used to simulate the satellite response to the incident radiation, and to calculate an effective ''response file'' for converting the source counts into fluxes and spectra. We provide details of the geometry and interaction physics, and validate the model by comparing the simulations of imaging and flux studies with observations. Spectroscopic validation of the mass model is discussed in a companion paper, Chattopadhyay et al.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The AstroSat mass model: Imaging and flux studies of off-axis sources with CZTI

et al. 2021

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“…This has been used to develop a program called CIFT: the CZTI Interface for Fast Transients ( [29]). The Earth Occultation Technique (EOT) has also been developed to study persistent sources at large off-axis angles and demonstrated by measuring the flux of the Crab nebula and pulsar, and measuring the variability of Cyg X-1 ( [30]). Measurements of polarization of prompt γ-ray emission from GRBs has also been reported by [31].…”

Section: Czti Data Products and Analysismentioning

confidence: 99%

The AstroSat Observatory

Singh¹

2022

Preprint

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AstroSat is India's first Ultra-violet (UV) and X-ray astronomy observatory in space. The satellite was launched by the Indian Space Research Organisation on a Polar Satellite Launch Vehicle on 28 September 2015 from Sriharikota Range north of Chennai on the eastern coast of India. AstroSat carries five scientific instruments and one auxiliary instrument. Four of these consist of co-aligned telescopes and detectors mounted on a common deck of the satellite to observe stars and galaxies simultaneously in the near-and far-UV wavelengths and a broad range of X-ray energies (0.3 -80 keV). The fifth instrument consists of three X-ray detectors and is mounted on a rotating platform on a side that is oriented 90 degrees with respect to the other instruments to scan the sky for X-ray transients. An auxiliary instrument monitors the charged particle environment in the path of the satellite.

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“…For astronomical satellites working in the low-Earth orbit with certain inclinations and precessions, the emission from particular sources can sometimes be attenuated by the atmosphere or occulted by Earth. For all-sky field-of-view (FOV) X/γ-ray monitors, the Earth Occultation Technique (EOT) is first proposed to image or measure the flux and energy spectrum of high-energy astrophysical sources (Zhang et al 1993;Harmon et al 2002Harmon et al , 2004Wilson-Hodge et al 2012;Rodi et al 2014;Singhal et al 2021). For X-ray satellites with a small FOV, the EOT usually serves as a remote sensing measurement of atmospheric density (Determan et al 2007;Katsuda et al 2021Katsuda et al , 2022Yu et al 2022aYu et al , 2022b.…”

Section: Introductionmentioning

confidence: 99%

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

Xue

Xiong

et al. 2022

ApJS

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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.

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Using collimated CZTI as all-sky X-ray detector based on Earth occultation technique

Cited by 8 publications

References 15 publications

The AstroSat mass model: Imaging and flux studies of off-axis sources with CZTI

The AstroSat mass model: Imaging and flux studies of off-axis sources with CZTI

The AstroSat Observatory

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

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