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Post-impulsive millimeter emission of the 2022-05-04 solar flare

G. G. Motorina, Yu. T. Tsap, V. V. Smirnova, A. S. Morgachev, A. S. Motorin

TL;DR

This study analyzes the post-impulsive millimeter emission of the SOL2022-05-04T08:45 (M5.7) solar flare using $93~\mathrm{GHz}$ data from RT-7.5 and multiwavelength EUV/X-ray observations. A differential emission measure (DEM) is reconstructed over $0.5-25~\mathrm{MK}$ to predict thermal bremsstrahlung at $93~\mathrm{GHz}$ and is compared to the observed mm flux. The comparison shows coronal plasma can contribute about $\sim 20\%$ of the mm flux for large source areas, while the observed flux is $26\pm 3.9~\mathrm{sfu}$ and the DEM-based prediction is $\sim 6~\mathrm{sfu}$, indicating additional non-coronal contributions. The near-flat mm spectrum at the peak ($\alpha \approx -0.06$ between $93$ and $15.4~\mathrm{GHz}$) and EUV enhancements near $T \sim 1~\mathrm{MK}$ support a multi-thermal emission scenario that may include coronal rain, implying mm observations can diagnose coronal condensation during flare decay.

Abstract

The present work aims at analyzing the nature of millimeter (mm) emission observed during the post-impulsive phase of the solar flare SOL2022-05-04T08:45 (M5.7), detected by the RT-7.5 radio telescope of the Bauman Moscow State Technical University at 93 GHz. We investigate the relationship of mm and extreme ultraviolet (EUV) emission with variations in the temperature and coronal plasma emission measure obtained from SDO/AIA and GOES data. The results show that the enhanced mm emission at the post-impulsive phase of the flare coincides with the increase of EUV emission, indicating a connection with moderately hot (~1 MK) plasma. Based on the calculation of the differential emission measure, we determine the parameters of the post-impulsive flare plasma and conclude that the optically thin coronal plasma may contribute of about 20% to the mm emission.

Post-impulsive millimeter emission of the 2022-05-04 solar flare

TL;DR

This study analyzes the post-impulsive millimeter emission of the SOL2022-05-04T08:45 (M5.7) solar flare using data from RT-7.5 and multiwavelength EUV/X-ray observations. A differential emission measure (DEM) is reconstructed over to predict thermal bremsstrahlung at and is compared to the observed mm flux. The comparison shows coronal plasma can contribute about of the mm flux for large source areas, while the observed flux is and the DEM-based prediction is , indicating additional non-coronal contributions. The near-flat mm spectrum at the peak ( between and ) and EUV enhancements near support a multi-thermal emission scenario that may include coronal rain, implying mm observations can diagnose coronal condensation during flare decay.

Abstract

The present work aims at analyzing the nature of millimeter (mm) emission observed during the post-impulsive phase of the solar flare SOL2022-05-04T08:45 (M5.7), detected by the RT-7.5 radio telescope of the Bauman Moscow State Technical University at 93 GHz. We investigate the relationship of mm and extreme ultraviolet (EUV) emission with variations in the temperature and coronal plasma emission measure obtained from SDO/AIA and GOES data. The results show that the enhanced mm emission at the post-impulsive phase of the flare coincides with the increase of EUV emission, indicating a connection with moderately hot (~1 MK) plasma. Based on the calculation of the differential emission measure, we determine the parameters of the post-impulsive flare plasma and conclude that the optically thin coronal plasma may contribute of about 20% to the mm emission.
Paper Structure (3 sections, 4 figures)

This paper contains 3 sections, 4 figures.

Table of Contents

  1. Introduction
  2. OBSERVATIONAL DATA AND PROCESSING
  3. DISCUSSION OF RESULTS AND CONCLUSIONS

Figures (4)

  • Figure 1: Light curves of SOL2022-05-04T08:45. Panel (a), from top to bottom: 1-8 and 0.5-4 Å (GOES); 20–80 keV (Konus- Wind); 2.8 and 5.8 GHz (SRH); 4.9, 8.8, 15.4 GHz (RSTN, San-Vito), 11.2 GHz (Metsähovi); 93 GHz (3.2 mm) (RT-7.5); panel (b): 171, 193, 211, 335 Å from the ROI, shown in Fig. \ref{['fig3']} (right panel); panel (c): 94, 131, 304, 1600 Å from the ROI.
  • Figure 2: The radio flux density spectrum of the flare at the peak time (09:15:30 UT).
  • Figure 3: Left panel: SDO/AIA maps indicating the region of interest (ROI) taken during the post-impulsive phase of the 2022 May 4 flare. Right panel: DEM from the ROI close to the peak time (09:15:30 UT).
  • Figure 4: Comparison of the temporal profiles of SOL2022-05-04T08:45: EM, T, and mm emission (left panel); calculated (SDO plasma) and observed (RT-7.5) mm emission at 93 GHz and optical thicknes (right panel).