EBL Absorption Signatures in DC2 Data

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Presentation transcript:

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

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.

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

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

BPL Results  BPL Kneiske Kneiske High-UV Primack Stecker

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

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

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

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

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

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

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.