Measuring the GRH and the cosmological parameters with MAGIC Oscar Blanch IFAE, Universitat Autònoma de Barcelona ISCRA 2002 June 2002

Any  that crosses cosmological distances through the universe interacts with the EBL. This produces a reduction factor e -  in the  ray flux, where  is the Optical Depth. Optical Depth & GRH Then the GRH is defined at each redshift “z” as the energy “E” that fulfils:

Extragalactic Background Light Current Data New Generation of  Telescopes The pair production cross-section has its maximum at: New  Telescopes (30GeV-30TeV), can look at the unexplored zone.

Gamma Ray Horizon Predictions Several SED at redshift 0 Several Metagalactic Radiation Field

GRH measurement with MAGIC Extrapolation of Mkn 421 We extrapolated the Mkn421 flux to estimate what the observations of sources at higher redshift will be. There are two effects to be taken into account: Flux reduction due to the increase in distance Displacement of the absorption energy cutoff (GRH). For that we used the previous computation of the GRH and the Optical Depth ->  (E) = 1,   E b And then the extrapolated flux is fitted with the following expression:

The Gamma Ray Horizon in MAGIC 1 source like Mkn421 at several redshifts. 30 GeV Energy Threshold

Cosmological Parameters Best fit current values All the current experiments combined lead to: The GRH gives an independent method for their calculation. Redshift dependence

Sensitivity

Systematic Error from SED Measurement of cosmological parameters Combine measurement at each redshift  reduction of statistic error

Conclusions Magic (and other  T) will be able to measure the GRH up to high redshifts, with a reasonable significance (although it depends on the AGNs that will be found). The GRH (and the Optical Depth) will give information on the SED either about its value at z=0 (low redshift) and its evolution (high redshift). The GRH gives a method to calculate some cosmological parameter that is independent on the current ones. The precision that we would get depends on the number of AGN but we can achieve precision at the order of the current measurements.