Blazars as beamlights to probe the EBL

1. Nijil Mankuzhiyil (INFN, Udine U.) Massimo Persic (INAF+INFN, Trieste) Fabrizio Tavecchio (INAF, Milano) Blazars as beamlights to probe the EBL Problem: EBL, emitted SED: both unknown ! Aim: measure nEBL(z) at different redshifts  local normalization, cosmic evolution Tools: homogeneous set @ different redshifts v one same model (parameters) at all z blazars (e.g., High-Peaked BLs [HBLs] ) Emission physics: simple  one-zone SSC emission v synchrotron + compton, PL electron spectrum B.Lott’s talk

2. One-zone SSC: model parameters: Plasma blob:R, B, dj Electron pop:n0, a1, a2, Ebr, Emin, Emax Tavecchio + 2001 ApJ, 554, 725 Kino+ 2002

3. The method (1) T T T T T T T T Simultaneous multi-nobs’s: voptical+X-rays+HE g-ray + VHE g-ray Model SED:use SED w/out (EBL-affected) VHEg-ray data:  c2-minimization  SSC model (check structure of multi-D parameter space) simulated data

4. …the method (2) Extrapolate model SED into VHE regime  “intrinsic” blazar VHE emissionObserved vs “intrinsic” emission  tgg(E,z) s i m u l a t e d d a t a simulated data Assume (concordance) cosmology  nEBL(e,zj) (parametric: å anjen) simulated data

5. Checking the method … locally PKS 2155-304 Aharonian+ 2009 ApJ, 696, L150 z = 0.12 SSC param’s gmin= 1 gbr1 = 1.4´104 gbr2 = 2.3´105 gmax= 3´106 a1= 1.3 a2= 3.2 a3= 4.3 B = 0.018 G R = 1.5´1017cm d = 32 FERMI Swift ATOM HESS RXTE EBL de-absorbed … caveat… … assumed electron spectrum is triple-PL …

6. … our effort data: Aharonian+ 2009 ApJ, 696, L150 SSC parameters from c2 minim. ne=150 cm-3 gmin= 1 gbr = 2.9´104 gmax= 8´105 a1 = 1.8 a2 = 3.8 B = 0.056 G R = 3.87´1016 cm d = 29.2 ATOM Swift, RXTE Fermi H.E.S.S. observed R Dt »12 hr  OK

7. l l l p r e l i m i n a r y l l

8. Malkan & Stecker 1998 p r e l i m i n a r y l l Stecker & de Jager 1998 l l Stecker 1999 z=0.12

9. Franceschini + 2008 p r e l i m i n a r y z=0.3 z=0.1 l l z=0.03 l z=0.01 l z=0.003 z=0.12

10. For EBL photon energies e > 2(mec2)2 / E (1-cosf) b(E,e,f) º [1 – 2(mec2)2 / Ee (1-cosf)]1/2 s(E,e,f) Heitler 1960 s(E,e)max by (for head-on collision) » 2.5 Eg, TeV mm IACT: 0.05 – 100 TeV 0.12 – 250 mm Optical depth 0 £z£zs e > 2(mec2)2 / [Ex(1+z)2] xº1-cosf t(Eg,z) = òdl/dz òx/2 ònEBL(e) s(2xEe/(1+z)2) de dx dz Stecker 1971 = c/(1+z) dtlookback/dz cosmology nEBL(en,zj) = å an,jen nEBL(e,z) unknown  parameterize … work in progress … Stecker 1999

11. Conclusion Cons: lindirect measurement of EBL lmethod depends on blazar model Pros: lunbiased method lno assumptions on EBL, blazar SED lSSC well tested locally on different emission states Check: lon local (z=0.12) blazar PKS 2155-304 ldeduced t’s within reasonable range OK Aim: l to probe EBL out to z»1 with Fermi/LAT + current/upcoming enhanced IACTs ( + x-ray, optical tel’s ) (  long live Fermi to see CTA / AGIS !! ) Need: lsimultaneous multi-n obs’s of several blazars in shells of z l possibly each source seen @ different levels of activity (to increase statistics)  plan simultaneous obs’s involving IACTs + Fermi + X-rays + optical

12. Thanks