4. Solar Hard X-ray Flares

This kind of transient events, owing to the X-ray activity of the Sun, has been already mentioned in chapter 3. In particular, these events include the solar flares with high HR, at least over the canonical threshold set to $0.3$. All the transient events belonging to this class, exhibit the following properties:

(a)

the error box of the arrival direction estimate includes the Sun position (this almost always means that, among the four GRBM units, # 2 ranks first as for both total counts and peak count rate);

(b)

the Sun has really undergone an X-ray flaring activity at the off-line trigger time, according to the continuous monitoring of the Sun operated by the NASA mission GOES

(c)

the BeppoSAX spacecraft must be at day-time; in other words, the Sun cannot be Earth-blocked from the BeppoSAX point of view, trivially.

(d)

the HR is just above the $0.3$ threshold, and has to be $<0.5$ anyhow;

When the last condition is not fulfilled, the transient event is not raised to the GRB class, but, instead, to the Likely GRBs, or to the Suspected GRBs, simply, depending on the other features.