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.
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