Analysis of intermittency in submillimeter radio and hard x-ray data during the impulsive phase of a solar flare

We present an analysis of intermittent processes occurring during the impulsive phase of the flare SOL2012-03-13, using hard X-rays and submillimeter radio data. Intermittency is a key characteristic in turbulent plasmas and has so far only been analyzed for hard X-ray data. Since in a typical flare the same accelerated electron population is believed to produce both hard X-rays and gyrosynchrotron radiation, we compare the two time profiles by searching for intermittency signatures. For this, we define a cross-wavelet power spectrum, which is used to obtain the local intermittency measure, or LIMLIM. When greater than three, the square LIMLIM coefficients indicate a local intermittent process. The LIM2LIM2 coefficient distribution in time and scale helps to identify avalanche or cascade energy release processes. We find two different and well-separated intermittent behaviors in the submillimeter data: for scales greater than 20 s, a broad distribution during the rising and maximum phases of the emission seems to favor a cascade process; for scales below 1 s, short pulses centered on the peak time are representative of avalanches. When applying the same analysis to hard X-rays, we find that only the scales above 10 s produce a distribution related to a cascade energy fragmentation. Our results suggest that different acceleration mechanisms are responsible for tens of keV and MeV energy ranges of electrons

The 6 September 2017 X9 super flare observed from submillimeter to mid-IR

Active Region 12673 is the most productive active region of solar cycle 24: in a few days of early September 2017, four X‐class and 27 M‐class flares occurred. SOL2017‐09‐06T12:00, an X9.3 flare also produced a two‐ribbon white light emission across the sunspot detected by Solar Dynamics Orbiter/Helioseismic and Magnetic Imager. The flare was observed at 212 and 405 GHz with the arcminute‐sized beams of the Solar Submillimeter Telescope focal array while making a solar map and at 10 μm, with a 17 arcsec diffraction‐limited infrared camera. Images at 10 μm revealed that the sunspot gradually increased in brightness while the event proceeded, reaching a temperature similar to quiet Sun values. From the images we derive a lower bound limit of 180‐K flare peak excess brightness temperature or 7,000 sfu if we consider a similar size as the white light source. The rising phase of mid‐IR and white light is similar, although the latter decays faster, and the maximum of the mid‐IR and white light emission is ∼200 s delayed from the 15.4‐GHz peak occurrence. The submillimeter spectrum has a different origin than that of microwaves from 1 to 15 GHz, although it is not possible to draw a definitive conclusion about its emitting mechanism

The European Solar Telescope

The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems