X‐ray spectral observations of a solar active region corona

Abstract

We study the X‐ray flux and electron temperature variation of the corona above a solar active region. Electron temperatures are determined using data from the S xv channel of the Bragg crystal spectrometer (BCS) instrument on board the Yohkoh satellite. The active region, designated NOAA AR 7999, rotated from just inside the west solar limb to beyond the limb over the period December 2–4, 1996, allowing us to map the electron temperature as a function of height in the active region's corona. Consistent with previous findings, we find two components to the active region coronal temperature, with a hotter (Te ≳5.0 MK) component due to transient flares and microflares, and a cooler component present in between the times of the microflares. There is a steady decrease in the frequency of occurrence of flares and microflares as the occultation progresses, implying that the flaring structures are low lying. For the cool component, the average electron temperature is about 4.5 MK when the region is just inside the limb, and gradually decreases to under 3.0 MK as the region rotates around the limb, indicating that temperature decreases with height.