Sky Exposure

In addition to some factors like the GRBM efficiency as a function of the local direction, that make the probability that a GRB may be detected from a given local direction higher than from other directions, therefore introducing a certain local anisotropy, here the effect of the Earth blockage is studied.

We define the sky exposure as the fraction of time that a given (local or celestial) direction was not Earth-blocked from the GRBM/BeppoSAX line of sight, with no care about the GRBM efficiency corresponding to that direction. If the ``visibility'' definition of a given source or direction is recalled to mind (sec. ), it turns out that the total sky exposure of a given direction coincides with the its total visibility fraction.

Obviously, this exposure depends on the orbit; since this is an equatorial orbit with a $\sim 3-4\rm ^{\circ}$ inclination with respect to the equatorial plane, it is expected that the maximum exposure should be in proximity of the celestial poles, and the minimum exposure in the nearby of the celestial equator ( $\delta = 0\rm ^{\circ}$).