4:15 PM - 4:30 PM
[PEM16-04] Sustained Gamma-Ray Emission: Case study of an X-class flare occurred on 7 March 2012
Keywords:solar flare, coronal mass ejection, particle acceleration, gamma-rays
Thanks to the high sensitivity of Fermi's Large Area Telescope (Fermi/LAT), pion-decay gamma-ray emissions which last beyond the impulsive phase of the associated flare for minutes to hours (sustained gamma-ray emission; SGRE) were observed in more than 40 solar flares from 2011 to 2022. However, the origin of SGRE has not been understood well. Gopalswamy and his colleagues found that the duration of SGRE has a good correlation with the end frequency and the duration of corresponding type-II radio burst. This indicates that high-energy protons producing SGRE are closely related with CME shock. In this situation, we had an ISEE international workshop in October 2023 in order to discuss and confirm this scenario.
After the workshop, we are looking for any signature of high-energy protons precipitating into the lower solar atmosphere (chromosphere and photosphere) after the impulsive phase of the corresponding solar flare. At first, we chose an X-class flare occurred on 7 March 2012 for this study. Because it has the event with the most intense gamma-ray emissions among the events which occurred daytime in Japan. This event showed that the gamma-ray source location (position of the center of gravity) changed in time after the flare. We think signatures of proton precipitation from the interplanetary space should appear at the open magnetic field regions, not at the closed magnetic field regions. Thus, we checked the open magnetic field regions on the solar surface and looked for any kind of counterpart of the gamma-ray emissions (SGRE) in other wavelengths there. Full sun images at 17Ghz observed with Nobeyama Radioheliograph is useful for this type of study. Actually, we found an enhancement at one of the open magnetic field regions, far from the flare site. We discuss if this is related with the precipitation of high-energy protons. Also, we reconsider the interpretation of SGRE with other observational results such as white-light, EUV, and so forth.
After the workshop, we are looking for any signature of high-energy protons precipitating into the lower solar atmosphere (chromosphere and photosphere) after the impulsive phase of the corresponding solar flare. At first, we chose an X-class flare occurred on 7 March 2012 for this study. Because it has the event with the most intense gamma-ray emissions among the events which occurred daytime in Japan. This event showed that the gamma-ray source location (position of the center of gravity) changed in time after the flare. We think signatures of proton precipitation from the interplanetary space should appear at the open magnetic field regions, not at the closed magnetic field regions. Thus, we checked the open magnetic field regions on the solar surface and looked for any kind of counterpart of the gamma-ray emissions (SGRE) in other wavelengths there. Full sun images at 17Ghz observed with Nobeyama Radioheliograph is useful for this type of study. Actually, we found an enhancement at one of the open magnetic field regions, far from the flare site. We discuss if this is related with the precipitation of high-energy protons. Also, we reconsider the interpretation of SGRE with other observational results such as white-light, EUV, and so forth.