"The GOES X-ray Flux plot contains 5 minute averages of solar X-ray output in the 1-8 Angstrom (0.1-0.8 nm) and 0.5-4.0 Angstrom (0.05-0.4 nm) passbands. Data from the SWPC Primary GOES X-ray satellite is shown. As of Feb 2008, no Secondary GOES X-ray satellite data is available. Some data dropouts will occur during satellite eclipses."
Source: NOAA / Space Weather Prediction Center
Read more: http://www.swpc.noaa.gov/rt_plots/xray_5m.html