1. C&A 8 May 06 1 Point Source Localization: Optimizing the CTBCORE cut Toby Burnett University of Washington

2. C&A 8 May 06 2 Recall the Simple PSF parameterization LATDOC AM-04355: We define a PDF in the angular deviation  with two parameters:  : a scale  : the power law Corner: defined by  Tail defined by  An example fit using all- gamma

3. C&A 8 May 06 3 The Classification Tree Analysis Recall that there are four trees, one for front and back, and whether a single track or vertex predicts a better PSF. They are combined in a single variable CTBCORE. The DC2 event class “class A” is defined by CTBCORE>0.35. This cut was not optimized: while increasing it reduces the effective area, it also dramatically improves the PSF, as Bill has shown:  Can we improve the pointing resolution by restricting CTBCORE? All gamma, class A Class A cut

4. C&A 8 May 06 4 Spectrum of source MRF0141_v1r2 at ra, dec=111.597000, -27.990000 level events sig fraction TS 6 515 0.00 +/- 0.02 -0 7 131 0.00 +/- 0.05 -0 8 41 0.27 +/- 0.11 11 9 18 0.93 +/- 0.13 37 10 19 1.00 +/- 0.14 42 11 10 0.97 +/- 0.18 21 12 20 1.00 +/- 0.18 49 13 32 1.00 +/- 0.23 98 258 Gradient delta ra dec error Ts 11166 0.0019 111.5970 -27.9900 0.0031 257.9995 685 0.0001 111.5988 -27.9890 0.0031 258.3586 *** good fit *** Localization Analysis Presented last week: http://d0.phys.washington.edu/~burnett/GLAST/AnaGroup/DC2_2_localization.ppt http://d0.phys.washington.edu/~burnett/GLAST/AnaGroup/DC2_2_localization.ppt –Based on UW simple likelihood function: the simple PSF + uniform background, one parameter describing the signal fraction in each of 8 energy bands. –Localization done by maximizing the total likelihood (or TS) with respect to position. –Output from /users/burnett/tools: two stages: spectrum, position Initial position for signal fraction fits Total TS: just add TS for each band Maximize total TS by varying position (fractions fixed) Projected error (deg) from likelihood curvature

5. C&A 8 May 06 5 Expected position Resolution See the LATDOC: projected resolution varies with , , and the efficiency  as Note that for the Gaussian case, , it becomes  /  N, where N is the total number of events (This ignores the effect of background, which degrades the resolution) So, as we increase CTBCORE, we expect  to increase, but  to decrease: is there an optimum?

6. C&A 8 May 06 6 Measurements from AllGamma The following plot was derived from PSF fits to class A front, integrating over all angles for each of the 8 energy bands, weighed for a E -2 signal. The effect is spectacular! The variation of  is flat. So, what about the counting factor  ?

7. C&A 8 May 06 7 The bottom Line CTBCORE>0.35 looks just fine: super job, Bill !