Articles written in Journal of Astrophysics and Astronomy
Volume 42 All articles Published: 3 July 2021 Article ID 0067 SCIENCE RESULTS
Exploring sub-MeV sensitivity of AstroSat–CZTI for ON-axis bright sources
ABHAY KUMAR TANMOY CHATTOPADHYAY SANTOSH V. VADAWALE A. R. RAO SOUMYA GUPTA N. P. S. MITHUN VARUN BHALERAO DIPANKAR BHATTACHARYA
The Cadmium–Zinc–Telluride Imager (CZTI) onboard AstroSat is designed for hard X-ray imaging and spectroscopy in the energy range of 20–100 keV. The CZT detectors are of 5-mm thickness and hence have good efficiency for Compton interactions beyond 100 keV. The polarisation analysis using CZTIrelies on such Compton events and have been verified experimentally. The same Compton events can also be used to extend the spectroscopy up to 380 keV. Further, it has been observed that about 20% pixels of the CZTI detector plane have low gain, and they are excluded from the primary spectroscopy. If these pixels are included, then the spectroscopic capability of CZTI can be extended up to 500 keV and further up to 700 keV with a better gain calibration in the future. Here we explore the possibility of using the Compton events as well as the low gain pixels to extend the spectroscopic energy range of CZTI for ON-axis bright X-ray sources. We demonstrate this technique using Crab observations and explore its sensitivity.
Volume 42 All articles Published: 21 July 2021 Article ID 0082 SCIENCE RESULTS
Sub-MeV spectroscopy with AstroSat-CZT imager for gamma ray bursts
TANMOY CHATTOPADHYAY SOUMYA GUPTA VIDUSHI SHARMA SHABNAM IYYANI AJAY RATHEESH N. P. S. MITHUN E. AARTHY SOURAV PALIT ABHAY KUMAR SANTOSH V. VADAWALE A. R. RAO VARUN BHALERAO DIPANKAR BHATTACHARYA
Cadmium–Zinc–Telluride Imager (CZTI) onboard AstroSat has been a prolific Gamma-Ray Burst (GRB) monitor. While the 2-pixel Compton scattered events (100–300 keV) are used to extract sensitive spectroscopic information, the inclusion of the low-gain pixels ($\sim$20% of the detector plane) aftercareful calibration extends the energy range of Compton energy spectra to 600 keV. The new feature also allows single-pixel spectroscopy of the GRBs to the sub-MeV range which is otherwise limited to 150 keV. We also introduced a new noise rejection algorithm in the analysis (‘Compton noise’). These new additionsnot only enhances the spectroscopic sensitivity of CZTI, but the sub-MeV spectroscopy will also allow proper characterization of the GRBs not detected by
Volume 44 All articles Published: 24 February 2023 Article ID 0014
Solar wind plasma variations with interplanetary magnetic field during solar cycles 22–24
PRITHVI RAJ SINGH ABHAY KUMAR SINGH TARUN KUMAR PANT
In this paper, we have studied the relationship between the monthly variations of solar wind plasma velocity, interplanetary magnetic field (IMF) and geomagnetic activity index (Ap) during solar cycles 22–24 (1986–2020). The modulation parameter ($\zeta=V*B$) is proportional to the product of solar windplasma velocity, $V$ and strength of the interplanetary magnetic field, $B$. We have investigated the periodicities and their evolution during solar cycles 22–24 using Fast Fourier Transform (FFT), RobPer periodogram and Continuous Wavelet Transformation methods. The significant periods present in the modulation parameter include the Rieger type, semi-annual period, annual period and quasi-biennial period (mid-term). In this study, we have found that the rotation rate at the base of the convection zone is $\sim$1.30 years. Quasi-biennial oscillations (QBOs) of solar wind plasma velocity, IMF, modulation parameters and Ap have been compared. The modulation parameter appears to be a better representative of the geomagnetic changes than the other two.
Volume 44, 2023
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