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Preliminary Post-DC2/Handoff Instrument Response Functions (IRFs) and Point Source Sensitivity

Preliminary Post-DC2/Handoff Instrument Response Functions (IRFs) and Point Source Sensitivity. Toby Burnett University of Washington. Generation of test data set (“all-gamma”). Energy : uniformly in log(energy) from 18 MeV to 178 (or 356 GeV) Angles : Uniform in upper GLAST hemisphere

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Preliminary Post-DC2/Handoff Instrument Response Functions (IRFs) and Point Source Sensitivity

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  1. PreliminaryPost-DC2/HandoffInstrument Response Functions (IRFs) and Point Source Sensitivity Toby Burnett University of Washington T. Burnett

  2. Generation of test data set (“all-gamma”) • Energy: uniformly in log(energy) from 18 MeV to 178 (or 356 GeV) • Angles: Uniform in upper GLAST hemisphere • Position: uniform over 6 m2 disk (1.38 m radius) perpendicular to incoming, centered at GLAST coordinate origin. • About 2/3 miss • Current Data set: 20 M generated • Bill used 2M. • Start with basic cuts z    y x T. Burnett

  3. Effective Area, FOV Loose cuts Count number in each bin, divide by total generated in that bin, multiply by 6 m^2 T. Burnett

  4. Angular detail (1-10 GeV) 66 cut 66 cut T. Burnett

  5. Acceptance: integrate over angles, >66 Relevant for scanning mode sensitivity T. Burnett

  6. PSF • Front (thin) vs. back (thick) – factor of 2 in width • Separate, measure independently • Energy dependence: E-0.8 • Factor of 100 from 100 MeV to 10 GeV! • Bin in energy, fit scaled deviation • CTBCORE • Introduced by Atwood • Function of other variables,trained to predict good PSF From Atwood T. Burnett

  7. PSF representation • Two traditional measures • Scale: 68% containment radius • Shape: ratio of 95% to 68% radius • (assume azimuthally symmetric) • Simple function has two parameters:  for scale,  for shape (power-law). T. Burnett

  8. PSF fits • Categories: front/back, 8 bins in log energy, 8 bins in cos() • Also fit combined angles, 0-66 Front,CTBCORE>0.5 Note: =2 corresponds to 95%/68% ratio =3. This is of course Monte Carlo: the beam test must validate it! T. Burnett

  9. Check PSF in CTBCORE intervals 3 Combined 0-66 degrees Data sets 4 2 1GeV 1 10GeV 100 GeV T. Burnett

  10. Point-source sensitivity • Figure of merit combining FOV, effective area, PSF • What is the weakest E-2 power law source, in the presence of the nominal EGRET extra galactic diffuse background, that is detectable with a likelihoodTS >25 for a one year livetime, in a scanning mode? • Current estimate: 4E-9 cm-2 s-1, E>100 MeV From GLAST LAT performance T. Burnett

  11. The ingredients: for each event class T. Burnett

  12. Sensitivity Calculation T. Burnett

  13. Point source sensitivity: Check TS for 4E-9 cm-2 s-1, one year livetime • E-2 power law • Standard EGRET extragalactic background • Combined 0-66 deg in one bin, scanning mode • Ignore effects of dispersion ‘5” requirement: (TS) > 25 T. Burnett

  14. Status/Plans • No post-DC2 surprises: parameterizations used then still seem applicable • Preliminary set of IRFs ready for Science Tools • Need to reconcile with beam test • Generate ~100M All-gamma data set T. Burnett

  15. Dispersion • R. Rando’s formula, compared with Gaussian with same variance T. Burnett

  16. Fit results (typical) 3.9% 3.7% Tail contents may be a problem: let’s cut on that good energy measurement guy! T. Burnett

  17. Cut on CTBBestEnergyProb>0.5 Reduced acceptance 2.4% ~0% Consequence for the sensitivity:TS = 15.5 +7.6 This tail was in the DC2 data T. Burnett

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