Impulsive phase heating and a coronal explosion in a solar flare

Abstract

The flare of 12 November 1980, 02∶50 UT, in Active Region 2779 (NOAA classification) was studied by using X-ray images obtained with the Hard X-Ray Imaging Spectrometer aboard NASA's Solar Maximum Mission. In a ten-minute period, between about 02∶44 and 02∶54 UT, some five short-lived impulsive bursts occurred. We found that the so-called ‘hard’ bursts (≳ 15 keV) are also detectable in low energy images. During that 10 min period - the impulsive phase - the heat input into the flare and the total number of energetic electrons increased practically exponentially, to reach their maximum values at 02∶54 UT. At the end of that period, when the thermal energy content of the flare was largest, a burst was observed, for the first time, to spread in a broad southern direction from an initially small area with a speed of about 50 km s−1. We have called this phenomenon a coronal explosion.