Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Multi-directional investigations on quiet time suprathermal ions measured by ASPEX-STEPS on-board Aditya L1

Aakash Gupta, Dibyendu Chakrabarty, Santosh Vadawale, Aveek Sarkar, Bijoy Dalal, Shiv Kumar Goyal, Jacob Sebastian, P. Janardhan, Nandita Srivastava, M. Shanmugam, Neeraj Kumar Tiwari, Aaditya Sarda, Piyush Sharma, Anil Bhardwaj, Prashant Kumar, Manan S. Shah, Bhas Bapat, Pranav R. Adhyaru, Arpit R. Patel, Hitesh Kumar Adalja, Abhishek Kumar, Tinkal Ladiya, Sushil Kumar, Nishant Singh, Deepak Kumar Painkra, Abhishek J. Verma, Swaroop Banerjee, K. P. Subramanian, M. B. Dadhania

TL;DR

The paper investigates quiet-time suprathermal ions using four directionally separated STEPS sensors on the ASPEX payload aboard Aditya L1 to quantify their spectral indices and test directional isotropy. It identifies quiet intervals with a mean–variance criterion, fits a power-law to the differential directional flux J ∝ E^{-m}, and compares directional results across detectors, including a rotation test. The results yield a near-universal spectral slope of $m \approx 2$ (i.e., $J \propto E^{-m}$ with $m \approx 2$) across all directions during 2024’s solar maximum, and after a first-order Compton-Getting correction, with minimal directional dependence. Elemental-abundance ratios from ACE/ULEIS reveal enrichment in $^3$He and Fe during quiet times, suggesting residual contributions from impulsive and gradual SEPs to the quiet-time pool, thereby supporting the isotropy assumption in Parker transport modeling.

Abstract

The origin, acceleration and anisotropy of suprathermal ions in the interplanetary medium during quiet periods have remained poorly understood issues in solar wind physics. To address these aspects, we derive the spectral indices for the quiet time suprathermal ions based on the measurements by the four directionally separated sensors that are part of the Supra-Thermal and Energetic Particle Spectrometer (STEPS) of Aditya Solar Wind Particle EXperiment (ASPEX) on-board Aditya L1 spacecraft. Three out of four STEPS sensors Parker Spiral (PS), Inter-Mediate (IM), Earth Pointing (EP) are in one plane (nearly aligned with the ecliptic plane) while the fourth sensor North Pointing (NP) is in a mutually orthogonal plane. The energy ranges covered by the PS, IM, EP and NP sensors are 0.36-1.32 MeV, 0.14-1.22 MeV, 0.39-1.33 MeV and 0.12-1.23 MeV respectively. The quiet intervals are identified during January November, 2024 and the derived spectral indices (differential directional flux versus energy) are found to be in the range of 2.0 for all directions in the time scale of a few days revealing isotropic nature of their distribution. Further analysis of elemental abundance ratios (3He/4He, Fe/O, and C/O) during the same quiet intervals obtained from the Ultra-Low Energy Isotope Spectrometer (ULEIS) on board the Advanced Composition Explorer (ACE) spacecraft suggests possible contributions from the leftover ions from the previous impulsive (Solar flares) and gradual events (CMEs) in the quiet time suprathermal ion pool.

Multi-directional investigations on quiet time suprathermal ions measured by ASPEX-STEPS on-board Aditya L1

TL;DR

The paper investigates quiet-time suprathermal ions using four directionally separated STEPS sensors on the ASPEX payload aboard Aditya L1 to quantify their spectral indices and test directional isotropy. It identifies quiet intervals with a mean–variance criterion, fits a power-law to the differential directional flux J ∝ E^{-m}, and compares directional results across detectors, including a rotation test. The results yield a near-universal spectral slope of (i.e., with ) across all directions during 2024’s solar maximum, and after a first-order Compton-Getting correction, with minimal directional dependence. Elemental-abundance ratios from ACE/ULEIS reveal enrichment in He and Fe during quiet times, suggesting residual contributions from impulsive and gradual SEPs to the quiet-time pool, thereby supporting the isotropy assumption in Parker transport modeling.

Abstract

The origin, acceleration and anisotropy of suprathermal ions in the interplanetary medium during quiet periods have remained poorly understood issues in solar wind physics. To address these aspects, we derive the spectral indices for the quiet time suprathermal ions based on the measurements by the four directionally separated sensors that are part of the Supra-Thermal and Energetic Particle Spectrometer (STEPS) of Aditya Solar Wind Particle EXperiment (ASPEX) on-board Aditya L1 spacecraft. Three out of four STEPS sensors Parker Spiral (PS), Inter-Mediate (IM), Earth Pointing (EP) are in one plane (nearly aligned with the ecliptic plane) while the fourth sensor North Pointing (NP) is in a mutually orthogonal plane. The energy ranges covered by the PS, IM, EP and NP sensors are 0.36-1.32 MeV, 0.14-1.22 MeV, 0.39-1.33 MeV and 0.12-1.23 MeV respectively. The quiet intervals are identified during January November, 2024 and the derived spectral indices (differential directional flux versus energy) are found to be in the range of 2.0 for all directions in the time scale of a few days revealing isotropic nature of their distribution. Further analysis of elemental abundance ratios (3He/4He, Fe/O, and C/O) during the same quiet intervals obtained from the Ultra-Low Energy Isotope Spectrometer (ULEIS) on board the Advanced Composition Explorer (ACE) spacecraft suggests possible contributions from the leftover ions from the previous impulsive (Solar flares) and gradual events (CMEs) in the quiet time suprathermal ion pool.

Paper Structure

This paper contains 11 sections, 2 equations, 10 figures.

Table of Contents

  1. Introduction
  2. Dataset
  3. Methodology
  4. Selection of quiet time
  5. Estimation of spectral index
  6. Results
  7. Common quiet time for PS, IM, EP and NP detectors
  8. Quiet time for individual detectors (PS, IM, EP and NP)
  9. Quiet time when AL1 was rotated (during November - 2024)
  10. Discussions
  11. Summary

Figures (10)

  • Figure 1: Mean versus Variance plots of the sorted (in ascending order) directional differential flux for Parker Spiral (PS), Earth Pointing (EP), North Pointing (NP), and Intermediate (IM) detectors of AL1-ASPEX-STEPS during the observational period from January to November 2024. The vertical red dashed line in each panel represents the threshold value of the flux below which the fluxes are considered as the quiet time flux and beyond which the fluxes are considered to be associated with transient events. The threshold values are also mentioned. The corresponding energy range is written at the top of each panel.
  • Figure 2: Panels a, b, c and d present the temporal variations of differential directional fluxes of suprathermal ions measured by PS, EP, IM and NP detectors of AL1-ASPEX-STEPS, respectively. Panels e, f, g, and h present the corresponding quiet time directional differential flux of suprathermal ions in PS, EP, IM and NP detectors, respectively. The energy channels for the panels are mentioned at the right side of the figure.
  • Figure 3: Plots of quiet time differential directional flux versus energy with spectral index and coefficient of determination ($R^2$) values mentioned in each subplot for the PS (a), IM (b), EP (c) and NP (d) directions of AL1-ASPEX-STEPS. Spectral indices are calculated by fitting only the linear part in this log-log plots. The range of energy for the fitted linear part is mentioned in each subplot for PS, IM, EP and NP in red, blue, green and magenta colors respectively.
  • Figure 4: Plots of quiet-time differential directional flux versus energy with spectral index values shown in each subplot for the PS (a–e), IM (f–j), EP (k–o), and NP (p–t) detectors of AL1-ASPEX-STEPS.
  • Figure 5: Plots of quiet time differential directional flux versus energy with spectral indices value mentioned in each subplot for the Parker Spiral (PS) detector of AL1-ASPEX-STEPS.
  • ...and 5 more figures