ebl absorption signatures in dc2 data
DESCRIPTION
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? - PowerPoint PPT PresentationTRANSCRIPT
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)
faint blazar(PL)
residual background
residual background
bright blazar (BPL+EBL)
galactic & EG
BPL Results
BPL KneiskeKneiske High-UVPrimackStecker
BPL Results
BPL PL
KneiskeKneiske High-UVPrimackStecker
BPL Results vs. PL Results
• PL E0 higher than BPL E0 for most sources
• Intrinsic breaks can pull E0 to lower energies
BP
L E
0 (
Ge
V)
PL E0 (GeV)
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!(Despite hand-holding)
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.