5:15 PM - 6:45 PM
[PEM14-P05] Study on the time evolution of the electron acceleration site in solar flares observed with NoRH and RHESSI
Keywords:solar flare, particle acceleration
A solar flare is an explosion phenomenon caused by magnetic reconnection. During a solar flare, it is well known that a large number of electrons are accelerated but the acceleration mechanism and location have not been revealed. In previous studies, Aschwanden+ estimated the height of an acceleration site by applying the Time of Flight (ToF) analysis to hard X-ray (HXR) data. Thus, they concluded it is located above the loop top. According to the flare model based on magnetic reconnection, the structure of the flare is grown up with time evolution. However, any signature for a continuous upward motion of the acceleration site has never been observed yet.
The simplest way to estimate the time evolution of the acceleration site is by applying ToF repeatedly for each HXR data. As our previous study, we calculated it in an M-class flare and concluded there is the possibility that the distance between the acceleration site and the footpoints was grown (JpGU2023 PEM14-P08). However, the time evolution of a structure has not been clearly revealed yet due to the lack of imaging data.
Therefore, for the next step, we decided to analyze the relatively large solar flares simultaneously observed with RHESSI, NoRH, Fermi, and SDO which are listed in Krucker+ 2020. For applying ToF repeatedly for a flare, we have to choose some suitable time windows from each HXR data. In this study, we defined a few short-duration spikes in each flare as suitable time windows by using the method developed in Aschwanden+ 1995a. Among 40 flares listed in the paper, we selected 3 solar flares which have at least several individual intensity peaks in the higher energy band (49.9 – 101.4 keV). For each time window, we calculated the time delay between the lower energy channel (26.3 - 49.9 keV) and the higher energy channel for these spikes using the same ToF analysis method in our previous study. As a result, we got a time series of delays for these three flares. The delays are scattered around zero and we couldn’t find any tendencies in these flares. This means that the acceleration site does not show any significant continuous upward motion in these flares. On the other hand, some flares had a spike that had a large time delay in the later phase. We will discuss what causes this large delay with HXR and microwave images.
The simplest way to estimate the time evolution of the acceleration site is by applying ToF repeatedly for each HXR data. As our previous study, we calculated it in an M-class flare and concluded there is the possibility that the distance between the acceleration site and the footpoints was grown (JpGU2023 PEM14-P08). However, the time evolution of a structure has not been clearly revealed yet due to the lack of imaging data.
Therefore, for the next step, we decided to analyze the relatively large solar flares simultaneously observed with RHESSI, NoRH, Fermi, and SDO which are listed in Krucker+ 2020. For applying ToF repeatedly for a flare, we have to choose some suitable time windows from each HXR data. In this study, we defined a few short-duration spikes in each flare as suitable time windows by using the method developed in Aschwanden+ 1995a. Among 40 flares listed in the paper, we selected 3 solar flares which have at least several individual intensity peaks in the higher energy band (49.9 – 101.4 keV). For each time window, we calculated the time delay between the lower energy channel (26.3 - 49.9 keV) and the higher energy channel for these spikes using the same ToF analysis method in our previous study. As a result, we got a time series of delays for these three flares. The delays are scattered around zero and we couldn’t find any tendencies in these flares. This means that the acceleration site does not show any significant continuous upward motion in these flares. On the other hand, some flares had a spike that had a large time delay in the later phase. We will discuss what causes this large delay with HXR and microwave images.