Quasi-periodic pulsations (QPP) of gamma-ray emission with a period of about 40 s are found in a single loop X-class solar flare on 2005 January 01 at photon energies up to 2-6 MeV with the SOlar Neutrons and Gamma-rays (SONG) experiment aboard the CORONAS-F mission. The oscillations are also found to be present in the microwave emission detected with the Nobeyama Radioheliograph, and in the hard X-ray and low energy gamma-ray channels of RHESSI. Periodogram and correlation analysis show that the 40 s QPP of microwave, hard X-ray and gamma-ray emission are almost synchronous in all observation bands. Analysis of the spatial structure of hard X-ray and low energy (80-225 keV) gamma-ray QPP with RHESSI reveal synchronous while asymmetric QPP at both footpoints of the flaring loop. The difference between the averaged hard X-ray fluxes coming from the two footpoint sources is found to oscillate with a period of about 13 s for five cycles in the highest emission stage of the flare. The proposed mechanism generating the 40 s QPP is a triggering of magnetic reconnection by a kink oscillation in a nearby loop. The 13 s periodicity could be produced by the second harmonics of the sausage mode of the flaring loop.

Abstract. Electromagnetic (radio, visible-light, UV, EUV, X-ray and gamma-ray) emission generated by solar and stellar flares often contains pronounced quasi-periodic pulsations (QPP). Physical mechanisms responsible for the generation of long-period QPP (with the periods longer than one second) are likely to be associated with MHD processes. The observed modulation depths, periods and anharmonicity of QPP suggest that they can be linked with some kind of MHD auto-oscillations, e.g. an oscillatory regime of magnetic reconnection. Such regimes, of both spontaneous and induced nature, have been observed in resistive-MHD numerical simulations. The oscillations are essentially nonlinear and non-stationary. We demonstrate that a promising novel method for their analysis is the Empirical Mode Decomposition technique.

Context. Quasi-periodic pulsations (QPPs) are a common feature of solar and stellar flares, and so the nature of these pulsations should be understood in order to fully understand flares. Aims. We investigate the properties of a set of solar flares originating from a single active region that exhibit QPPs, and in particular look for any indication of the QPP periods relating to active region properties (namely photospheric area, bipole separation distance, and average magnetic field strength at the photosphere), as might be expected if the characteristic timescale of the pulsations corresponds to a characteristic length scale of the structure from which the pulsations originate. The active region studied, known as NOAA 12172/12192/12209, was unusually long-lived and persisted for over three Carrington rotations between September and November 2014. During this time a total of 181 flares were observed by GOES. Methods. Data from the GOES/XRS, SDO/EVE/ESP, Fermi/GBM, Vernov/DRGE and Nobeyama Radioheliograph observatories were used to determine if QPPs were present in the flares. For the soft X-ray GOES/XRS and EVE/ESP data, the time derivative of the signal was used so that any variability in the impulsive phase of the flare was emphasised. Periodogram power spectra of the time series data (without any form of detrending) were inspected, and flares with a peak above the 95% confidence level in the power spectrum were labelled as having candidate QPPs. The confidence levels were determined taking full account of data uncertainties and the possible presence of red noise. Active region properties were determined using SDO/HMI line of sight magnetogram data. Results. A total of 37 flares (20% of the sample) show good evidence of having stationary or weakly non-stationary QPPs, and some of the pulsations can be seen in data from multiple instruments and in different wavebands. Because the detection method used was rather conservative, this may be a lower bound for the true number of flares with QPPs. The QPP periods were found to show a weak correlation with the flare amplitude and duration, but this is likely due to an observational bias. A stronger correlation was found between the QPP period and duration of the QPP signal, which can be partially but not entirely explained by observational constraints. No correlations were found with the active region area, bipole separation distance, or average magnetic field strength. Conclusions. The fact that a substantial fraction of the flare sample showed evidence of QPPs using a strict detection method with minimal processing of the data demonstrates that these QPPs are a real phenomenon, which cannot be explained by the presence of red noise or the superposition of multiple unrelated flares. The lack of correlation between the QPP periods and active region properties implies that the small-scale structure of the active region is important, and/or that different QPP mechanisms act in different cases.

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The dayside magnetosphere and proton radiation belt were analyzed during unusual magnetic storm on 21 January 2005. We have found that from 1712 to 2400 UT, the subsolar magnetopause was continuously located inside geosynchronous orbit due to strong compression. The compression was extremely strong from 1846 to 2035 UT when the dense plasma of fast erupting filament produced the solar wind dynamic pressure that peaked up to > 100 nPa, and during the first time, the upstream solar wind was observed at geosynchronous orbit for almost 2 h. Under the extreme compression, the outer magnetosphere at L > 5 was pushed inward, and the outer radiation belt particles moved earthward, became adiabatically accelerated, and accumulated in the inner magnetosphere at L < 4 that produced the intensified ring current with an exceptionally long lifetime. The observations were compared with predictions of various empirical and first-principles models. All the models failed to predict the magnetospheric dynamics under the extreme compression when the minimal magnetopause distance was estimated to be~3 RE. The inconsistencies might result from distortions of plasma measurements by extreme heliospheric conditions consisting in very fast solar wind streams and intense fluxes of solar energetic particles. We speculated that anomalous dynamics of the magnetosphere could be well described by the models if the He abundance in the solar wind was assumed to be > 20%, which is well appropriate for erupting filaments and which is in agreement with the upper 27% threshold for the He/H ratio obtained from Cluster measurements.

We studied a solar flare with pronounced quasi-periodic pulsations detected in the microwave, X-ray, and radio bands. We used the methods of correlation, Fourier, and wavelet analyses to examine the temporal fine structures and relationships between the time profiles in each wave band. We found that the time profiles of the microwaves, hard X-rays and type III radio bursts vary quasiperiodically with the common period of 40-50 s. The average amplitude of the variations is high, above 30% of the background flux level and reaching 80% after the flare maximum. We did not find the periodicity in either the thermal X-ray flux component or source size dynamics. Our findings indicate that the detected periodicity is likely to be associated with periodic dynamics in the injection of non-thermal electrons, that can be produced by periodic modulation of magnetic reconnection.Kupriyanova elena.kupriyanova@kuleuven.be Kashapova

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