The Data Archive Coverage

At the Physics Department of the University of Ferrara (Italy), a near-complete version of the GRBM data archive is continuously maintained and updated by the high energy astrophysics team by means of a proper software, the GRBMS.

The current situation (October 2001) of the GRBM archive can be summarized in terms of observation time: we limit our attention only to the normal OPs, starting from July 1996, when the first OPs with regular scientific data became available: while the total time elapsed is $\sim$1919 days, i.e. $\sim 1.66$x$10^8$ s, the total time duration of all the normal OPs is $\sim 1.34$x$10^8$ s: thus, it comes out that the fraction of time elapsed in normal pointing mode is $\sim$ 81% of the whole time interval. The total time of the overall set of OPs currently available is $\sim 1.17$x$10^8$ s, i.e. $\sim$ 87% of the total duration of the normal OPs.

The hole in the current data archive, represented by the lacking OPs with normal pointings, that amount to $\sim$ 13% of the whole normal pointing observation time, is going to be filled in, in collaboration with the SDC people.

Currently, we conclude that the total time coverage of the overall set of OPs with normal pointing (i.e., with fixed satellite attitude) presently available in our GRBM archive is $\sim 0.81 \times 0.87 \simeq$ 70% out of the total time elapsed since July 1996. Furthermore, out of this 70%, the time spent in the nearby of the SAGA, during which the GRBM HVs are periodically switched off ($\sim$ 15-20 min/orbit), has to be excluded; therefore, by assuming an average time of 18 min/orbit spent over the SAGA, which looks quite reasonable, the corresponding fraction comes out to be $\sim$ 17-18% per orbit: thus, only for the 82-83% out the 70%, that is 57-58% out of the total elapsed time is covered by 1 s ratemeters, currently available in our GRBM data archive.

This fraction is needed for estimating the sky exposure of the GRBM and, therefore, particularly for estimating the mean GRB rate as measured with GRBM (sec. ).