1. EBL Absorption Signatures in DC2 Data
Jennifer Carson (SLAC)
DC2 closeout meeting
June 1, 2006

2. Motivation How well can we measure EBL absorption in 55 days of data?
How sure can we be that we are distinguishing intrinsic spectral breaks from absorption signatures?
Fit spectra with broken power law model + absorption.
Compare results to simple power law fits.

3. Basic Procedure v2 of catalog
10° regions around LR’s 9 sources, 20° source regions
Only class A events
Diffuse components: extragalactic, galactic, high-energy residual, low-energy residual
Diffuse prefactors allowed to float in fits
All catalog point sources in FOV included (fixed PLs)
Broken power law model with EBL absorption (“BPLExpCutoff”): prefactor, 2 indices, break energy, Eabs, P1
 = (E – Eabs) / P1
Likelihood twice: DRMNGB for convergence, MINUIT for errors

4. Example Fits bright blazar (BPL+EBL) bright blazar (BPL+EBL) galactic
& EG
residual
background
residual
background
faint blazar(PL)

5. BPL Results
 BPL
Kneiske
Kneiske High-UV
Primack
Stecker

6. BPL Results
 BPL
 PL
Kneiske
Kneiske High-UV
Primack
Stecker

7. BPL Results vs. PL Results
BPL E0 (GeV)
PL E0 (GeV)
PL E0 higher than BPL E0 for most sources
Intrinsic breaks can pull E0 to lower energies

8. High-Redshift Sources
Found all sources with z > 2 in ASDC catalog (10)
ROI = 5°, source region = 15°

9. High-Redshift Sources
Found all sources with z > 2 in ASDC catalog (10)
ROI = 5°, source region = 15°
Can’t get good fits!

10. Fit Comparison: Idea Three types of fits:
Broken power law + fixed EBL absorption
Broken power law + no EBL absorption
Simple power law + floating EBL absorption
Four free parameters in each fit
Test statistic  goodness of fit

11. Fit Comparison: Results
red: TSBPL+EBL – TSBPL
blue: TSBPL+EBL – TSPL+EBL
TS generally better for BPL+EBL vs. pure BPL
TS generally better for BPL+EBL vs. PL+EBL

12. Conclusions
In < 2 months, difficult to constrain the EBL – no models ruled out
PL & BPL results are close, but BPL generally predicts higher E0 values
Especially difficult measure E0 for z > 2 sources
TS indicates that:
BPL+EBL better fit than PL+EBL
BPL+EBL better fit than pure BPL
High-energy residuals made finding E0 even harder
Future work
More data! What would a year of data tell us?
Automated search for flares + spectral analysis
Improve cuts to remove high-energy residual.
Need likelihood to converge reliably with correct errors.