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 one same model (parameters) at all z

blazars (e.g., High-Peaked BLs [HBLs] )

Emission physics: simple one-zone SSC emission

synchrotron + compton, PL electron spectrum

Nijil Mankuzhiyil (INFN, Udine U.) Massimo Persic (INAF+INFN, Trieste) Fabrizio Tavecchio (INAF, Milano)

One-zone SSC: model parameters:Plasma blob: R, B, j

Electron pop: n0, 1, 2, Ebr, Emin, Emax

Kino+ 2002

Tavecchio + 2001ApJ, 554, 725

Simultaneous multi- obs’s: opticalX-rays HE-ray VHE -ray

Model SED: use SED w/out (EBL-affected) VHE -ray data: 2-minimization SSC model(check structure of multi-D parameter space)

TT

TTTTTT

simulated data

The method (1)

Extrapolate model SED into VHE regime “intrinsic” blazar VHE emission

Observed vs “intrinsic” emission (E,z)

Assume (concordance) cosmology nEBL(,zj) (parametric: anj n)

s i m u l a t e d d a t a

simulated data

simulated data

…the method (2)

EBL de-absorbed

Aharonian+ 2009ApJ, 696, L150

HESS

FERMI

RXTE

ATOM

… assumed electron spectrum is triple-PL …

… caveat…

Swift

Checking the method … locallyPKS 2155-304z = 0.12

SSC param’smin= 1br1 = 1.4104

br2 = 2.3105

max= 3106

1 = 1.32 = 3.23 = 4.3

B = 0.018 GR = 1.51017

cm= 32

data: Aharonian+ 2009 ApJ, 696, L150

… our effort

H.E.S.S.

Fermi

ATOM Swift, RXTE

R t 12 hr OK

observed

SSC parametersfrom 2 minim.

ne=150 cm

min= 1br = 2.9104

max= 8105

1 = 1.82 = 3.8

B = 0.056 GR = 3.871016 cm= 29.2

p

r

e

l

i

m

i

n

a

r

y

Stecker 1999

z=0.12

p r e l

i m i

n a r y

Stecker & de Jager 1998

Malkan & Stecker 1998

Franceschini + 2008

z=0.1

z=0.003

z=0.01z=0.03

z=0.3

z=0.12

p r

e l

i m

i

n a

r

y

(E,)max by (for head-on collision)

2.5 E, TeV

m

Heitler 1960

(E,z) = dl/dz x/2 nEBL() (2xE/(1+z)2) ddx dz

(E,,) [1 – 2(mec2)2 / E (1-cos)]1/2

0 z zs

> 2(mec2)2 / [Ex(1+z)2]

For EBL photon energies > 2(mec2)2 / E (1-cos)

x 1-cos

nEBL(,z) unknown parameterize nEBL(nzj) = an,j n

(E,,)

Stecker 1971

cosmology

Stecker 1999

Optical depth

Conclusion

Cons: indirect measurement of EBL method depends on blazar model

Pros: unbiased method no assumptions on EBL, blazar SED SSC well tested locally on different emission states

Need: simultaneous multi- obs’s of several blazars in shells of z possibly each source seen @ different levels of activity (to increase statistics)

plan simultaneous obs’s involving IACTs + Fermi + X-rays + optical

Aim: 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 !! )

Check: on local (z=0.12) blazar PKS 2155-304 deduced ’s within reasonable range

Thanks