9:45 AM - 10:00 AM
[PEM14-03] Sun-as-a-star Analysis of the X1.6 flare on 2023 August 5: Post-flare Loops Observed in Soft X-ray, EUV, and Hα
Keywords:Solar flares, Stellar flares, Post-flare loops, Multiwavelength observation
Post-flare loops are loop-like plasmas observed during the decay phase of typical solar flares. Recently, superflares, which emit energy more than 1033 erg, have been discovered in various stars (e.g. Okamoto+ 2021), and many observations suggest that their basic mechanism is similar to that of solar flares. For example, filament/prominence eruptions, fundamental elements of standard solar flares as well as post-flare loops, have also been observed with superflares (Namekata+ 2022, 2023). These results are supported by the similarity with the spatially integrated solar data obtained by Sun-as-a-star analyses (Namekata+2022, Otsu+ 2022). However, the spatially integrated data of solar post-flare loops have not been fully investigated, and it is not yet clear how post-flare loops are observed in stellar cases.
In this study, we performed the Sun-as-a-star analysis of the X1.6 flare that occurred near the northwest limb on 2023 August 5 using GOES (soft X-ray, ~ 107 K), SDO/AIA (EUV, >105 K) and SMART/SDDI at Hida Observatory, Kyoto University (H-alpha line, ∼104 K), focusing on post flare loops. As a result, the spatially-integrated spectrum of the H-alpha line showed emission near the line center and simultaneous redshifted (< 100 km/s) and blueshifted (< 70 km/s) absorptions corresponding to the plasma flowing down along the post-flare loops. In the previous study, the post-flare loops of an M1.1 flare which occurred near the disk center of the Sun showed only redshifted (< 150 km/s) absorption (Otsu+2022). The difference in shifted absorptions between the present X1.6 and previous M1.1 flares can be explained by the line-of-sight projection effect due to the different location of their occurrences. The light curve of the H-alpha line for the X1.6 flare showed two distinct peaks corresponding to the flare ribbons and the post-flare loops. The H-alpha peak corresponding to the post-flare loops showed time delays of about 13 and 2.4 min with the GOES soft X-ray and AIA 171 A peaks, respectively, which are consistent with the radiative cooling timescale. This result indicates that the cooling process of stellar post-flare loops from hot to cool plasmas can also be detected in spatially integrated data of multi-wavelength observations in soft X-ray to H-alpha.
In this study, we performed the Sun-as-a-star analysis of the X1.6 flare that occurred near the northwest limb on 2023 August 5 using GOES (soft X-ray, ~ 107 K), SDO/AIA (EUV, >105 K) and SMART/SDDI at Hida Observatory, Kyoto University (H-alpha line, ∼104 K), focusing on post flare loops. As a result, the spatially-integrated spectrum of the H-alpha line showed emission near the line center and simultaneous redshifted (< 100 km/s) and blueshifted (< 70 km/s) absorptions corresponding to the plasma flowing down along the post-flare loops. In the previous study, the post-flare loops of an M1.1 flare which occurred near the disk center of the Sun showed only redshifted (< 150 km/s) absorption (Otsu+2022). The difference in shifted absorptions between the present X1.6 and previous M1.1 flares can be explained by the line-of-sight projection effect due to the different location of their occurrences. The light curve of the H-alpha line for the X1.6 flare showed two distinct peaks corresponding to the flare ribbons and the post-flare loops. The H-alpha peak corresponding to the post-flare loops showed time delays of about 13 and 2.4 min with the GOES soft X-ray and AIA 171 A peaks, respectively, which are consistent with the radiative cooling timescale. This result indicates that the cooling process of stellar post-flare loops from hot to cool plasmas can also be detected in spatially integrated data of multi-wavelength observations in soft X-ray to H-alpha.