Sources of Quasi-periodic Pulses in the Flare of 18 August 2012

Abstract

We analyzed spatial and spectral characteristics of quasi-periodic pulses (QPP) for the 18 August 2012 limb flare, using new data from a complex of spectral and imaging instruments developed by the Siberian Solar Radio Telescope team and the Wind/Konus gamma-ray spectrometer. A sequence of broadband pulses with periods of approximately ten seconds were observed in Xrays at energies between 25 keV and 300 keV, and in microwaves at frequencies from a few GHz up to 34 GHz during an interval of one minute. The QPP Xray source was located slightly above the limb where the south legs of large and small EUV loop systems were close to each other. Before the QPPs the soft X-ray emission and the Ramaty High Energy Solar Spectroscopic Imager signal from the energy channels below 25 keV were gradually arising for several minutes at the same location. It was found that each X-ray pulse showed the soft-hard-soft behavior. The 17 and 34 GHz microwave source were at footpoints of the small loop system and the source emitting in the 4.2 -7.4 GHz band in the large one. The QPPs were probably generated by modulation of acceleration processes in the energy release site. Analyzing radio spectra we determined the plasma parameters in the radio sources. The microwave pulses could be explained by relatively weak variations of the spectrum hardness of emitting electrons.

Rapid Variability in the SOL2011-08-04 Flare: Implications for Electron Acceleration

“…The inverted bell shape of the spectra is typical for the gyrosynchrotron emission. Both spectra are flat in the 3.75-9.4 GHz range, which evidences the contribution to the emission of more than one source or, in a general case, of a spatial nonuniformity of the source (Lee & Gary 1994;Altyntsev et al 2016;Fleishman et al 2016b). The spectrum shapes are similar before and at the subpeak, but the difference is weaker at the optically thick part at low frequencies.…”

The 26 December 2001 Solar Event Responsible for GLE63. I. Observations of a Major Long-Duration Flare with the Siberian Solar Radio Telescope

“…In the preceding studies of microwave flare emissions, the sources observed by the SSRT at 5.7 GHz were typically associated with loop-top regions (e.g. Altyntsev et al, 2002Altyntsev et al, , 2007Altyntsev et al, , 2016Meshalkina et al, 2012, and others). In the 26 December 2001 flare, two distinct microwave sources were observed.…”

“…The usage of the SSRT data in studies of flares has been limited (e.g. Altyntsev et al, 2002Altyntsev et al, , 2007Altyntsev et al, , 2016Meshalkina et al, 2012;Alissandrakis et al, 2013). The 1D-mode observations of a higher time resolution have also been involved, especially in studies of microwave sources on short time scales.…”

Flare SOL2012-07-06: On the Origin of the Circular Polarization Reversal Between 17 GHz and 34 GHz

“…The interaction site, seen as the main source in hard X-rays and in microwaves, is located near the common footpoint of the loops. Recently such flares have been discussed by Altyntsev et al (2016) and . Figure 3.…”

“…Gyrosynchrotron sources at high frequencies are often located close to the flare loop footpoints where the magnetic field exceeds several hundred Gauss, before lower frequencies are emitted from greater heights. Flares initiated by an interaction of two loops of rather different size have been reported (Hanaoka, 1997;Nishio et al, 1997;Altyntsev et al, 2016;. The NoRH polarization images at 17 GHz showed footpoints of a small loop and the SSRT observed a large loop at 5.7 GHz.…”