[P-EM11] Frontiers in solar physics

[PEM11-P02] Statistical Study of Appearance Timing of H-alpha Postflare Loops: Simple Scaling Law Based on Radiative Cooling

*Takato Otsu¹, Ayumi Asai¹, Kai Ikuta², Kazunari Shibata³ (1.Astronomical Observatory, Kyoto University, 2.The University of Tokyo, 3.Kwasan Observatory, Kyoto University)

Keywords:Solar flares, Stellar flares, Postflare loops

Postflare loops are important components of the standard flare model as well as flare ribbons and prominence eruptions, and their existence has been observationally suggested even in stellar flares (e.g., Wollmann+ 2023). To correctly understand dynamics of stellar flares, it is important to clarify how postflare loops are observed in spatially integrated data. Recently, Otsu+ (2024) investigated spatially integrated data of a typical solar flare and found that the secondary peak following the soft X-ray peak in the spatially integrated H-alpha light curve which comes from postflare loops. This result indicates that postflare loops can be detected even in spatially integrated stellar data. However, a secondary peak in H-alpha can appear due to other factors such as another flare and an associated prominence eruption. Therefore, it is necessary to quantitatively clarify what determines the appearance timing of the H-alpha postflare loops for investigating stellar postflare loops in detail. In this study, we statistically investigated the appearance timing of the H-alpha postflare loops using solar H-alpha data observed by SMART and Sartorius telescopes at Hida and Kwasan Observatories, respectively. We found negative correlation of the time difference between the soft X-ray peak time and the appearance timing of the H-alpha postflare loops (Δt) and the soft X-ray peak flux (F_X). This correlation is consistent with the scaling relation between radiative cooling time scale (τ_rad) and soft X-ray peak flux τ_rad∝F_X^-0.5, which is derived from their dependence on electron density (n_e): τ_rad∝n_e^-1 and F_X∝n_e². This consistency (Δt≈τ_rad) means that the appearance timing of the H-alpha postflare loops relative to a soft X-rays peak time is determined by radiative cooling. We present the details of these results and discuss the future comparison with stellar observations. In addition, we discuss a method for estimating spatial scale of stellar flares using the obtained scaling relation.