Magnetic topology of a complex active region

We present a detailed analysis of the magnetic topology of AR 6233 on two consecutive days (August 28 and 29, 1990). We compare the location of the magnetic separatrices and separators with off-band Hα observations and other flare manifestations, such as intense non-thermal electron precipitation and high coronal pressure sites, for two flares that occurred on these days. Because transverse magnetograms indicate that strong magnetic shear is present along the longitudinal inversion line, where flare brightening are located, the observed photospheric magnetic field is modeled in an approach in which a combination of sources with current-free and non current-free magnetic held is used. This model allows us to obtain a better ht between the observed and modeled transverse held. Then, we find a closer relationship between separatrices and hare features. The results of a current-free and of a linear force-free approach are also discussed. As in other haring regions studied previously, chromospheric flare brightening are found on separatrices. The topological structure obtained for these flares is rather complex and cannot be explained by classical flare models. We find that the connectivity of field lines may change drastically from one edge of an Ha; ribbon to the other. Electron precipitation and high coronal pressure sites, and some photospheric intense currents are also found in the immediate vicinity of separatrices. The early kernels of August 28 flare are found closer to the separatrices of the non-potential held, while the later are closer to those of the potential held. All these results agree with the hypothesis that magnetic energy is stored in field-aligned currents and released due to magnetic held reconnection, with a noticeable relaxation of the held, either at the separator region or on separatrices.Asociación Argentina de Astronomí

Imaging Spectroscopy of a White-Light Solar Flare

We report observations of a white-light solar flare (SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). The HMI data give us the first space-based high-resolution imaging spectroscopy of a white-light flare, including continuum, Doppler, and magnetic signatures for the photospheric FeI line at 6173.34{\AA} and its neighboring continuum. In the impulsive phase of the flare, a bright white-light kernel appears in each of the two magnetic footpoints. When the flare occurred, the spectral coverage of the HMI filtergrams (six equidistant samples spanning \pm172m{\AA} around nominal line center) encompassed the line core and the blue continuum sufficiently far from the core to eliminate significant Doppler crosstalk in the latter, which is otherwise a possibility for the extreme conditions in a white-light flare. RHESSI obtained complete hard X-ray and \Upsilon-ray spectra (this was the first \Upsilon-ray flare of Cycle 24). The FeI line appears to be shifted to the blue during the flare but does not go into emission; the contrast is nearly constant across the line profile. We did not detect a seismic wave from this event. The HMI data suggest stepwise changes of the line-of-sight magnetic field in the white-light footpoints.Comment: 14 pages, 7 figures, Accepted by Solar Physic

Polarisation de la raie H-alpha des Éruptions Solaires

International audienc

A ‘VISUAL’ APPROACH TO MENANDER - (A.K.) Petrides Menander, New Comedy and the Visual. Pp. xii + 322, ills. Cambridge: Cambridge University Press, 2014. Cased, £65, US$99. ISBN: 978-1-107-06843-8.

High-energy X-rays and gamma-rays from solar flares were discovered just over fifty years ago. Since that time, the standard for the interpretation of spatially integrated flare X-ray spectra at energies above several tens of keV has been the collisional thick-target model. After the launch of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in early 2002, X-ray spectra and images have been of sufficient quality to allow a greater focus on the energetic electrons responsible for the X-ray emission, including their origin and their interactions with the flare plasma and magnetic field. The result has been new insights into the flaring process, as well as more quantitative models for both electron acceleration and propagation, and for the flare environment with which the electrons interact. In this article we review our current understanding of electron acceleration, energy loss, and propagation in flares. Implications of these new results for the collisional thick-target model, for general flare models, and for future flare studies are discussed.Comment: This is an article from a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011