Flare SOL2012-07-06: on the origin of the circular polarization reversal between 17 GHz and 34 GHz by Altyntsev et al.*24 Oct 2017, 11:05 UTC
The new generations of multiwavelength radioheliographs with high spatial resolution will employ microwave imaging spectropolarimetry to recover flare topology and plasma parameters in the flare sources and along the wave propagation paths. The recorded polarization depends on the emission mechanism and emission regime (optically thick or thin), the emitting particle properties, and propagation effects. Here, we report an unusual flare, SOL2012-07-06T01:37, whose optically thin gyrosynchrotron emission of the main source displays an apparently ordinary mode sense of polarization in contrast to the classical theory that favors the extraordinary mode. This flare produced copious nonthermal emission in hard X-rays and in high-frequency microwaves up to 80 GHz (Figure 1).
Figure 1. Lightcurves of X–ray (RHESSI, red) and microwave fluxes (NoRP, black) in intensity (R+L, left) and in polarization (R−L, right). Plasma temperature profile calculated from the GOES data are shown in the left top panel. The RHESSI data are presented in arbitrary units.
It is found that the main flare source corresponds to an interaction site of two loops with greatly different sizes (Figure 2).
Figure 2. Flare structure. The grayscale background is a magnetogram taken at 01:39:00 UT (left panel) and an RMS polarization map at 17 GHz (right). Blue ...