Nijil Mankuzhiyil INFN Udine U Massimo Persic INAFINFN

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 n. EBL(z) at different redshifts local normalization, cosmic evolution Tools: homogeneous set @ different redshifts v one same model (parameters) at all z B. Lott’s talk blazars (e. g. , High-Peaked BLs [HBLs] ) Emission physics: simple one-zone SSC emission v synchrotron + compton, PL electron spectrum

One-zone SSC: model parameters: Tavecchio + 2001 Plasma blob: R, B, dj Ap. J, 554, 725 Electron pop: n 0, a 1, a 2, Ebr, Emin, Emax Kino+ 2002

The method (1) Simultaneous multi-n obs’s: v optical + X-rays + HE g-ray + VHE g-ray Model SED: use SED w/out (EBL-affected) VHE g-ray data: c 2 -minimization SSC model (check structure of multi-D parameter space) T T simulated data T T T

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

Checking the method … locally SSC param’s gmin= 1 gbr 1 = 1. 4´ 104 gbr 2 = 2. 3´ 105 gmax= 3´ 106 a 1 = 1. 3 a 2 = 3. 2 a 3 = 4. 3 PKS 2155 -304 z = 0. 12 Aharonian+ 2009 Ap. J, 696, L 150 FERMI ATOM Swift HESS RXTE B = 0. 018 G R = 1. 5´ 1017 cm d = 32 EBL de-absorbed … caveat… … assumed electron spectrum is triple-PL …

… our effort data: Aharonian+ 2009 Ap. J, 696, L 150 SSC parameters from c 2 minim. ne=150 cm-3 gmin= 1 gbr = 2. 9´ 104 gmax= 8´ 105 a 1 = 1. 8 a 2 = 3. 8 ATOM Swift, RXTE H. E. S. S. B = 0. 056 G R = 3. 87´ 1016 cm d = 29. 2 R Dt » 12 h r Fermi OK observed

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

Malkan & Stecker 1998 p r e l l i m i l n r a l z=0. 12 y l Stecker & de Jager 1998 Stecker 1999

Franceschini + 2008 p r e l i l m i n a y r . 3 0 z= l l l . 1 z=0. 03 0 = z z=0. 0 1 03 z=0. 0 z=0. 12

For EBL photon energies e > 2(mec 2)2 / E (1 -cosf) s(E, e, f) b(E, e, f) º [1 – 2(mec 2)2 / Ee (1 -cosf)]1/2 Heitler 1960 s(E, e) max by (for head-on collision) » 2. 5 Eg, Te. V mm – 100 5 0. 0 IACT: Optical depth 0 £ zs x º 1 -cos f Te. V 50 mm 2 – 2 1 0. e > 2(mec 2)2 / [Ex(1+z)2] t(Eg, z) = òdl/dz òx/2 òn. EBL(e) s(2 x. Ee/(1+z)2) de dx dz = c/(1+z) dtlookback /dz Stecker 1971 cosmology n. EBL(e, z) unknown parameterize n. EBL(en, zj) = å an, j en … work in progress … Stecker 1999

Conclusion Cons: l indirect measurement of EBL l method depends on blazar model Pros: l Check: l Aim: l Need: l unbiased method l no assumptions on EBL, blazar SED l SSC well tested locally on different emission states on local (z=0. 12) blazar PKS 2155 -304 OK l deduced t’s within reasonable range 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 !! ) simultaneous 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

Thanks