arXiv subjects

Hiteshkumar L. Adalja

Publications and source records attributed to Hiteshkumar L. Adalja.

6 recordsLinked to original sources

arXiv2025

Evidence for in situ particle energization during the May-2024 event based on ASPEX instrument on board Aditya-L1

The interaction between interplanetary Coronal Mass Ejection (ICME) structures can alter the geo-effectiveness of the ICME events in myriad ways. Many aspects of these interaction processes are not well-understood till date. Using the energy spectra measured in two mutually orthogonal top hat analyzers (THA 1 and 2), which are part of the Solar Wind Ion Spectrometer (SWIS) subsystem of the Aditya Solar Wind Particle EXperiment (ASPEX) on board India's Aditya L1 mission, we gain insights into intricate features of ICME ICME interactions during May 2024 solar event. We report here an unprecedented two-orthogonal-plane perspective of ICME ICME interactions for the first time from the L1 point. The investigation reveals a special interaction region formed by the propagation of the forward shock driven by complex ejecta in the preceding ICME. The interaction causes the formation of a downstream region spanning over 13 hours, which propagates in the interplanetary medium. The observations reveal that this region serves as a site for proton and alpha particle energization, and the particles within this region get distributed from one plane to the other. The presence of forward shock and particle energization is confirmed by the energetic particle flux measurements by the SupraThermal and Energetic Particle Spectrometer (STEPS) of ASPEX. These observations provide an unprecedented perspective on how solar wind ions become energized and distributed in an ICME-ICME interaction region.

astro-ph.SR↗

arXiv2025

One Year of ASPEX-STEPS Operation: Characteristic Features, Observations and Science Potential

The SupraThermal and Energetic Particle Spectrometer (STEPS), a subsystem of the Aditya Solar wind Particle EXperiment (ASPEX) onboard India's Aditya-L1 satellite, is designed to study different aspects of energetic particles in the interplanetary medium from the Sun-Earth L1 point using six detector units oriented in different directions. This article presents details of the one-year operation (08 January 2024 - 28 February 2025) of the AL1-ASPEX-STEPS after the insertion of the satellite into the final halo orbit around the L1 point with emphasis on performance, science observations, and scientific potentials. Four out of six AL1-ASPEX-STEPS units exhibit a stable detector response throughout the observation period, confirming operational robustness. This work also includes the temporal variation of particle fluxes, spectra of ions during selected quiet times and transient events, and cross-comparisons with existing instruments at the L1 point. A strong correlation (with coefficient of determination, R2 ~ 0.9) is observed in the cross-comparison study, establishing the reliability of the AL1- ASPEX-STEPS observations. AL1-ASPEX-STEPS also captures different forms of energetic ion spectra similar to those observed by previous missions. These results underscore the instrument's potential to contribute significantly to the study of energetic particle acceleration, transport, and long-term space weather monitoring from the Sun-Earth L1 vantage point.

physics.space-ph↗

arXiv2025

One year of ASPEX-SWIS operation -- Characteristic features, observations and science potential

The Aditya-L1 mission, India's first dedicated solar observatory positioned at the first Lagrange point (L1) of the Sun-Earth system, carries the Solar Wind Ion Spectrometer (SWIS) as part of the ASPEX payload suite. Even before settling into its Halo orbit, SWIS has been providing nearly continuous in-situ measurements of solar wind ion spectra. Moments of the velocity distribution functions (VDFs) have been calculated to derive key solar wind parameters such as density, bulk speed, and temperature. In this study, we assess the performance of SWIS (hereafter referred to as AL1-ASPEX-SWIS) by comparing its measurements with contemporaneous data from the Wind and DSCOVR missions. In this study, we assess the performance of SWIS (hereafter referred to as AL1-ASPEX-SWIS) by comparing its measurements with contemporaneous data from the Wind and DSCOVR missions. A detailed case study of the interplanetary coronal mass ejection (ICME) event on August 7, 2024, is presented, where sharp changes in bulk speed, thermal speed, and number density were found to be well-aligned with independent observations-confirming the instrument's ability to capture dynamic solar wind features. Spectral analysis of kinetic fluctuations revealed a well-defined inertial range with a spectral slope consistent with magnetohydrodynamic (MHD) turbulence. Furthermore, a 17-month statistical comparison (from January 2024 to May 2025) shows a strong correlation in bulk velocity (R2 = 0.94 with Wind), with expected variations in thermal speed and density arising from differences between instruments. These findings demonstrate the scientific value of AL1-ASPEX-SWIS for monitoring both transient solar events and long-term solar wind conditions.

astro-ph.SR↗

arXiv2022

Experimental verification of off-axis polarimetry with Cadmium Zinc Telluride detectors of AstroSat-CZT Imager

The Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat consists of an array of a large number of pixellated CZT detectors capable of measuring the polarization of incident hard X-rays. The polarization measurement capability of CZTI for on-axis sources was experimentally confirmed before the launch. CZTI has yielded tantalizing results on the X-ray polarization of the Crab nebula and pulsar in the energy range of 100 - 380 keV. CZTI has also contributed to the measurement of prompt emission polarization for several Gamma-Ray Bursts (GRBs). However, polarization measurements of off-axis sources like GRBs are challenging. It is vital to experimentally calibrate the CZTI sensitivity to off-axis sources to enhance the credence of the measurements. In this context, we report the verification of the off-axis polarimetric capability of pixellated CZT detectors through the controlled experiments carried out with a CZT detector similar to that used in CZTI and extensive Geant4 simulations of the experimental set-up. Our current results show that the CZT detectors can be used to measure the polarization of bright GRBs up to off-axis angles of ~60 degrees. However, at incidence angles between 45-60 degrees, there might be some systematic effects which needs to be taken into account while interpreting the measured polarisation fraction.

astro-ph.IM↗

arXiv2020

Solar X-ray Monitor On Board the Chandrayaan-2 Orbiter: In-flight Performance and Science Prospects

The Solar X-ray Monitor (abbreviated as XSM) on board India's Chandrayaan-2 mission is designed to carry out broadband spectroscopy of the Sun from lunar orbit. It observes the Sun as a star and measures the spectrum every second in the soft X-ray band of 1 - 15 keV with an energy resolution better than 180 eV at 5.9 keV. The primary objective of the XSM is to provide the incident solar spectrum for the X-ray fluorescence spectroscopy experiment on the Chandrayaan-2 orbiter, which aims to generate elemental abundance maps of the lunar surface. However, observations with the XSM can independently be used to study the Sun as well. The Chandrayaan-2 mission was launched on 22 July 2019, and the XSM began nominal operations, in lunar orbit, from September 2019. The in-flight observations, so far, have shown that its spectral performance has been identical to that on the ground. Measurements of the effective area from ground calibration were found to require some refinement, which has been carried out using solar observations at different incident angles. It also has been shown that the XSM is sensitive enough to detect solar activity well below A-class. This makes the investigations of microflares and the quiet solar corona feasible in addition to the study of the evolution of physical parameters during intense flares. This article presents the in-flight performance and calibration of the XSM instrument and discusses some specific science cases that can be addressed using observations with the XSM.

astro-ph.SR↗

arXiv2020

Ground Calibration of Solar X-ray Monitor On-board Chandrayaan-2 Orbiter

Chandrayaan-2, the second Indian mission to the Moon, carries a spectrometer called the Solar X-ray Monitor (XSM) to perform soft X-ray spectral measurements of the Sun while a companion payload measures the fluorescence emission from the Moon. Together these two payloads will provide quantitative estimates of elemental abundances on the lunar surface. XSM is also expected to provide significant contributions to the solar X-ray studies with its highest time cadence and energy resolution spectral measurements. For this purpose, the XSM employs a Silicon Drift Detector and carries out energy measurements of incident photons in the 1 -- 15 keV range with a resolution of less than 180 eV at 5.9 keV, over a wide range of solar X-ray intensities. Extensive ground calibration experiments have been carried out with the XSM using laboratory X-ray sources as well as X-ray beam-line facilities to determine the instrument response matrix parameters required for quantitative spectral analysis. This includes measurements of gain, spectral redistribution function, and effective area, under various observing conditions. The capability of the XSM to maintain its spectral performance at high incident flux as well as the dead-time and pile-up characteristics have also been investigated. The results of these ground calibration experiments of the XSM payload are presented in this article.

astro-ph.IM↗