1. GLAST background review dec-7-05 1 Simulating rates: the big picture Incoming rate into the 6 m 2 sphere: is it right? Corresponding trigger rate: implies 15% deadtime: too high! Downlink rate: saturates our bandwidth allocation? one full day

2. GLAST background review dec-7-05 2 Where do all those numbers come from? From a flux to a rate max rate here: 30/m 2 /sr/s Note: this plot, one of many, was generated from the same code that we use: in the Mizuno representation, the secondary electrons are isotropic, and independent of geomagnetic latitude primary secondary

3. GLAST background review dec-7-05 3 A “rootplot” representation of the electrons

4. GLAST background review dec-7-05 4 Reality check on the rates The total rate for any component takes the differential rate and: –integrates over energies from E min (10 MeV) to E max (1 TeV) –integrates over all solid angle (4  ) –multiplies by the cross sectional area (6 m 2 ) of the enclosing sphere For the secondary electrons < 100 MeV, this calculation is: –(30/m 2 /sr/s) x ln(100/10) x (4  sr) x (6 m 2 ) = 5.2 kHz. The measured value for all energies, from test_DataChallenge, is 6.7 kHz. –the difference is quite consistent with the integral above 100 MeV.

5. GLAST background review dec-7-05 5 The next steps 1.Generate a time based on the rate (exponential) 2.Select an energy from the flux integrated over angles 3.Select a direction for the given energy three possible reference frames: celestial, local, GLAST 4.Select a position uniformly on the perpendicular disk 5.Propagate the particle into the sphere, using Geant 6.If it hits the detector, examine the resulting data 7.If there is a trigger, run the Onboard filter 8.If it passes the filter, run the reconstruction and save (“downlink”) the event