Task 2.1 Multi-frequency and spectral analysis of solar flares
Deliverable
Report summary [Month 18]
Fig. 1 Time profiles of the proton and electron fluxes during the events in March 2003 (red color) and April 2004 (black color). The left panel shows an evolution of the SEP electron fluxes and the right panel shows the SEP proton fluxes. The time profiles of both events are plotted relative to zero time. The zero time is 19:12 UT for the SOL2003-Mar-17 event and 04:48 UT for the SOL2004-Apr-11 event.
We carried out the comparative analysis of the solar energetic particle (SEP) event properties and the indicators of acceleration processes in solar flares - the hard X-rays (HXR) and radio emission from microwaves to the meter-range. We focus our study on the two SEP events associated with solar flares with similar characteristics in HXR emission and the close location on solar disk. The proton flux in the SEP event associated with the weaker flare by GOES class in soft X-ray (SXR) (C9.6/SOL2004-Apr-11) was more than an order higher than in the SEP event associated with the more powerful solar flare (X1.5/SOL2003-Mar-17). At the same time, the electron fluxes in both SEP events were comparable (see Figure 1). Both flares were followed by CMEs with speed above 1000 km/s. The spectral properties of SEP proton and electron fluxes were opposite to each other. The SEP proton spectral index in the SOL2004-Apr-11 event was softer than in the SOL2003-Mar-17 event. In contrary, the SEP electron spectral index of the more proton-rich event was harder than in the other event.
Fig. 2 Comparison of the time profiles in the different spectral ranges (denoted with solid lines) and the time derivative of SXR flux by GOES (denoted with dotted line): a) 1−8 Å soft X-rays by GOES; b) the microwave flux at 15.5 GHz frequency; c) hard X-ray flux by SONG (the duration of this time profile has defined by the SONG observational record length); d) radio flux at 245 MHz. The time profiles of both events are plotted relative to zero time chosen at the maximum of the hard X-ray flux of each event. It is 18:57:59 UT for the SOL2003-Mar-17 event (the red lines) and 04:15:31 UT for the SOL2004-Apr-11 event (black lines). All profiles were normalized to the maximum value.
According to the SXR derivative (see Figure 2), the initial phase of SOL2004-Apr-11 flare looks similarly to the initial phase of the M-class flare with γ-ray emission (Ackermann et al., 2012; Kashapova et al., 2012). This fact indicates the first stage of acceleration which signatures were too weak to be detected by HXR observations. We also found that during the SOL2004-Apr-11 the first peak at the time profile of the SXR derivative was caused by electrons with energy about 12−25 keV and preceded the onset the type III radio bursts that are signatures of electrons going towards the interplanetary space. There was a very short burst temporally coinciding with the SXR derivative during the other flare. We can identify this burst as the type III. However, one can note that it occurred after the impulse phase of the SOL2003-Mar-17 event. The other flare acceleration parameters are very close.
The analysis of SEP fluxes and flare plasma parameters was done taking into account the magnetic topology of the active region (AR) and its evolution before and during the solar flares (see results in Task 2.2).
Publications
Andrey Bogomolov, Irina Myagkova, Ivan Myshyakov, Tsvetan Tsvetkov, Larisa Kashapova,
Rositsa Miteva. Comparative analysis of the proton generation efficiency during 17 March 2003 and 11 April 2004 solar flares, (2018) JASTP, Vol. 179, Pages 517-526 [DOI:10.1016/j.jastp.2018.08.010]
