Solar X-ray Flares

Among the very bright transient events, solar X-ray flares are the most relevant, comparable with the brightest GRBs. An example of typical solar flare light curve is shown in fig. . They distinguish from GRBs by their direction, of course, by their long duration (typically ranging from $10^2$ s to some minutes) and by their spectrum, which is softer than GRBs': this feature in particular has turned out very effective to the aim of an automatic identification (see next sections).

Figure: Example of solar X-ray flare detected by the GRBM, units 2+3, on April 15, 2001, at 13:44 UT (upper panel: GRBM band; lower panel: AC band). This flare shows a ``curious'' profile: the fast drop has been caused by the occultation of the Sun behind the Earth, as seen from the BeppoSAX point of view.