![[BL vs E spectrum]](view_bl.gif)
b(E,B1,B2) = 1 if E<F1 b(E,B1,B2) = F2 + F3 exp[(E-F1)/F4] otherwise
The relevant coefficients F (together with B1 and B2) are kept in files m{1,2,3}_blsel.coeff.
Fig. 4.12-I : MECS BL selection coefficients vs energy (click on figure to expand Y scale)
The following figure shows a typical energy-burst length image (number of counts vs PHA channel on X-axis, and BL channels on Y-axis, both ranging 0-255).
Fig. 4.12-II : example of E-BL image for an exposure taken on the ground (MPE Panter facility) This particular exposure is in Cu light (8.4 keV). The X and Y scale are in PHA and BL channels (both ranging 0-255).
The horizontal strip corresponds to the normal BL range, and contains the continuum underlying the line, the line itself (i.e. the events numbered as 1-2 in the event interaction figure), and the escape peak (fluorescence events numbered as 4). The vertical strip is due to events indicated with number 3 (recombination of primary and fluorescence at long BL). The lower oblique branch is due to events (not shown in quoted figure) absorbed in the scintillation region with a lower penetration depth (they produce a reduced amount of UV light, resulting in a shorter BL and a wrong PHA value).