a) GOES-12 X-ray flux in the 0.5−4.0 Å band (red line) and in the 1.0−8.0 Å band (blue line) on 17 January 2005. The graph shows the occurrence of an X3.8 flare, with a peak of intensity at 09:52 UT. b) Light curve showing the X-ray emission measured by RHESSI at different energy bands during the time interval 07:00−10:30 UT. c) RHESSI X-ray light curve showing in more detail the time interval 09:40−10:05 UT. The spikes are probably of instrumental origin.