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.

eeEBLHE

This produces a reduction factor e- in the ray flux, where is the Optical Depth.

2

42

1

2

22

00

12,2

,

zEx

cm

z

zxEzndx

dxzd

dtczdzE

Optical Depth & GRH

Then the GRH is defined at each redshift “z” as the energy “E” that fulfils:

1, zE

Extragalactic Background Light

Current Data

New Generation of Telescopes

The pair production cross-section has its maximum at:

TeV

Em 41.2

New Telescopes (30GeV-30TeV), can look at the unexplored zone.

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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

zz dE

dzrzr

dE

d

22

• Displacement of the absorption energy cutoff (GRH).For that we used the previous computation of the

GRH and the Optical Depth -> (E) = 1, Eb

b

EE

eEfdE

d

0

0

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

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Cosmological ParametersBest fit current values

All the current experiments combined lead to:

The GRH gives an independent method for their calculation.

Redshift dependence

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dp

zdEpzS HRG

p

Sensitivity

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Systematic Error from SED

Measurement of cosmological parameters

Combine measurement at each redshift reduction of statistic error

NH

H

,

,0

0

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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.