Analysis of the polarization degree distribution along limb flaring loop of July 19, 2012 S. Kuznetsov 1, A. Morgachev 1 V. Melnikov 2 Radiophysical Research Institute, Nizhny Novgorod, Russia 1 Pulkovo Observatory, Saint-Petersburg, Russia 2 14 th European Solar Physics Meeting 8 th -12 th September, 2014 Trinity College Dublin, Ireland 1

Introduction Inversion of the polarization sign of microwave gyrosynchrotron emission (extra-ordinary to ordinary) is a signature of some important peculiarities in solar flaring loops. Possible reasons for the inversion of polarization degree along solar flaring loops: - Anisotropy of accelerated electrons (Melnikov, Gorbikov, Pytakov 2009); - positron’s emission (Fleishman 2013); - twisted magnetic field lines 2

The main goal of the research is to find and analyze solar flares with inversion of the polarization along flaring loops. As an example we have considered the event of July 19, This event is M 7.7 class. 3 Aim of the research

4 Observational data We have used Nobeyama Radioheliograph for analysis of observational data. This instrument has a high temporal (0.1 sec for the flaring regime) and spatial resolution ( 10” for 17 GHz and 5” for 34 GHz).

Radio brightness distribution along flaring loops 5

Inversion of polarization degree along flaring loops 6

Size of the boxes – 10”x10” Number of boxes

Polarization degree distribution along flaring loops 8

9 Dynamics of the pol. degree along flaring loop

10 Dynamics of the pol. degree along flaring loop

11 Dynamics of the pol. degree along flaring loop Loop Top Southern Leg

12 In a magnetic loop, a part of injected electrons are trapped due to magnetic mirroring and the other part directly precipitates into the loss-cone. The trapped electrons are scattered due to Coulomb collisions and loose their energy and precipitate into the loss-cone. A real distribution strongly depends on the injection position in the loop and on the pitch-angle dependence of the injection function S(E, ,s,t), and also on time ( Melnikov et al. 2006; Gorbikov and Melnikov 2007 ). Non-stationary Fokker-Plank equation ( Lu and Petrosian 1988 ): Kinetics of Nonthermal Electrons in Magnetic Loops

13 Distribution of the polarization degree Case 1: Injection at the loop top Case 2: Injection near a footpoint Ordinary mode circular polarization  Signature of the longitudinal anisotropy Increase in X-mode polarization degree  signature of the perpendicular anisotropy Melnikov, Gorbikov, Pytakov 2009

Discussion 14 The possible reason of the inversion of the polarization degree can be positron’s influence. But due to very small quantity of positrons in solar flares this explanation is not possible. Another possible reason of this effect is the twisted magnetic field lines. The twist makes the viewing angle changing along a loop (for example, from less than 90 deg to more than 90deg). But, for our flaring loop we have regions where the polarization degree changes its sign with time. So, this reason is also unlikely. Anisotropy is a kinetic effect. We suppose that longitudinal anisotropy of accelerated electrons is a possible reason of the inversion of the polarization degree along flaring loop. This assumption is considered in detail in the poster of Alexander Morgachev (s.7-07).

Conclusions The inversion of the polarization degree during the flaring loop has been found. Polarization degree is negative for the footpoints. Polarization degree is positive for the loop top and for the leg of the flaring loop. Temporal dynamics of the polarization degree is different for different parts of the flaring loop. Changing the polarization degree along the flaring loop can be explained by the longitudinal pitch-angle distribution of emitting mildly relativistic electrons. 15