Temperature variability in X-ray bright points observed with Hinode/XRT

Abstract

Aims. Our aim is to investigate the variability in the temperature as a function of time among a sample of coronal X-ray bright points (XBPs). Methods. We analysed a 7-hour (17:00 UT - 24:00 UT) long time sequence of soft X-ray images observed almost simultaneously in two filters (Ti poly and Al mesh) on April 14, 2007 with XRay Telescope (XRT) on-board the Hinode mission. We identified and selected a sample of 14 XBPs and 2 background coronal regions for a detailed analysis. The light curves of XBPs have been derived using SolarSoft library in IDL. The temperature of XBPs was determined using the calibrated temperature response curves of the two filters by intensity ratio method. Results. We find that the XBPs show a high variability in their temperature and the average temperature ranges from 1.1 MK to 3.4 MK. The variations in the temperature are related to the different X-ray emission fluxes. These results suggest that XBPs of different temperatures may be present at the same height in the corona. It is evident from the results of time series that the heating rate of XBPs is highly variable on short time scales, and these variations provide a support for magnetic reconnection as the origin of XBPs.