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Cosmology with the New
Generation of Cherenkov
Telescopes
Oscar Blanch Bigas
IFAE, UAB
Seminari IEEC
15-XII-04
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Introduction
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
INTRODUCTION
-ray Astronomy
• Cosmic Rays hit the Earth’s atmosphere (1000 m-2 s-1):
–
–
–
–
–
What are their sources?
What is their chemical composition?
What are the astrophysical process of the acceleration?
How do they propagate through galactic and extragalactic space?
…
more than 99% are charged particles …
but they loose original direction
• CGRO & Whipple  breakthrough on -ray astronomy (0.1%).
– Production processes of -ray might also be responsible for the
production of the CR
• Light on Fundamental Physics: dark matter, antimatter,
quantum gravity, cosmology, ...
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
INTRODUCTION
Cosmology
• “Cosmological Principle”: homogeneous and isotropic universe.
 dr 2

2
2
2
2
ds  dt  R t 

r
d


r
sin

d

2

2
1

kr


2
2
• In the context of general relativity, the dynamics of the universe
is governed by the Friedmann equation.


R
2
2
 H2  Ho (1  mz)1  z   z2  z 
R

Where the redshift (z) is defined as: 1+z  R0 / R(t) and therefore
redshift and time are related by the lookback-time.
dt

dz

1 1  z 
H0 1  mz 1  z   z2  z  
Oscar Blanch Bigas
2

1
2
Seminari IEEC - 15-XII-04
The Cherenkov
Telescopes
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The Cherenkov Telescopes
New Generation of Cherenkov Telescopes
• Previous Situation:
– Energy gap between satellites (<10 GeV) and ground-based
Telescopes (>300 GeV).
– Extinction of number of sources in this gap :
For extragalactic sources  absorption due to Extragalactic
Background Light (EBL).
Ground-based
> 300 GeV
Satellites
< 10 GeV
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The Cherenkov Telescopes
The “Big” four
VERITAS
Montosa Canyon,
Arizona
MAGIC (2004)
Roque de los
Muchachos, Canary
Islands
HESS (2003)
Windhoek,
Namibia
CANGAROO III
Woomera,
Australia
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The Cherenkov Telescopes
Image Air erenkov Technique
Altitude (Km)
• IACT do not see the -ray hitting the atmosphere but the
erenkov light from the electro-magnetic shower developed in
the atmosphere (calorimeter with atmosphere as active material)
The light is collected and
focused on the camera
forming and image of the
electro-magnetic shower.
The image may come from a
pure electro-magnetic
shower (,e-) or from the
electro-magnetic part of
hadron showers (p,He,…).
Fast -pulse allow to reduce
background due to LONS
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The Cherenkov Telescopes
• The images formed by hadronic showers (background) and
electro-magnetic (signal) are different.
Photons point to the center!
Oscar Blanch Bigas
Protons do not!
Seminari IEEC - 15-XII-04
The Cherenkov Telescopes
Moreover, the shape is
also different and it is
usually described by
Hillas Parameters:
(width, length, dist,
alpha, ...)
They depend on energy
of incident  spectrum
from each source.
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC
Telescope
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC Telescope
• MAGIC requests:
–
–
–
–
Lowering as much as possible the Energy Threshold.
Maximum feasible sensitivity in the unexplored energy range.
Extragalactic sources  North Hemisphere.
Fast repositioning for GRB follow-ups  Light Telescope.
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC Telescope
A second Generation IACT - MAGIC
• An advanced 17 m Telescope based on a series of innovative
features.
17m Ø mirror
Ultralight alluminum panels
85%-90% reflectivity
3.5° FOV camera
577 pixels
Optical fiber analogic
transmission
2 level trigger &
300 MHz FADC
Oscar Blanch Bigas
Light carbon fiber tubes
65 ton total weight
Frame corrected using Active Mirror Control
Seminari IEEC - 15-XII-04
The MAGIC Telescope
The Frame
The largest telescope
mirror ever built by
Human Being: 240 m²
surface.
Light weight carbon fiber
structure.
17 tons : Dish + Mirrors
64 tons: Telescope
(fast positioning over
180 in 22s)
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC Telescope
The Reflector
Tessellated reflector:
– ~950 mirror elements
– 49.5 x 49.5 cm2
– All-aluminum, quartz coated,
diamond milled, internal heating
– >85% reflectivity in 300-650nm
Active mirror control: Use lasers to
recall panel positions when
telescope moves
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC Telescope
Camera and signal transmission
577 PMTs
Coating & Double crossing
Inner zone: 396 pixels of 0.1
Outer zone: 180 pixels of 0.2
Oscar Blanch Bigas
Optical analogic transmitters
160 m of fibres: short signal,
Seminari IEEC
optically decoupled,
cable- 15-XII-04
weigth,...
The MAGIC Telescope
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC Telescope
Signal Processing
Optical transmission over 162 m
1st Level Trigger: 2,3,4,5-fold next
neighbour
2nd Level: freely programmable
300 MHz, 8 Bit FADC.
Dynamic range: 2000.
DAQ: Continuous ~700 Hz
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC
Physics
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
The MAGIC Physics
AGNs
SNRs
Dark Matter
-RH & Cosmology
Quantum Gravity
effects
Pulsars
Oscar Blanch Bigas
GRBs
Seminari IEEC - 15-XII-04
The MAGIC Physics
Active Galactic Nuclei
Active Galactic Nuclei refers to galaxies with a central region
where high-energetic processes take place.
• AGN have been found in all
wavelength and they showed
emission up to TeV energies.
• Emission in jet produced by
electron or proton primaries?
• Highest variability in X-ray and
-ray.
• High energy -ray from very far
distances: Cosmology, Quantum
Gravity, ...
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Optical Depth
&
Gamma Ray Horizon
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Optical
Depth and GRH
Optical Depth
& Gamma
Ray Horizon
Concept - EBL absorption
High energy -rays travelling cosmological distances are
expected to be absorbed through their interactions with the EBL by:
   e e
The integration over the path travelled across the universe, which
depends on the source redshift (z), is the Optical Depth.
z
dt 2
x
0
dz 0
2 m
(E, z)   dz  c 
 dx 
 d  n, z  E, , x, z
Then the -ray flux is attenuated while travelling from the emission
point to the detection point.
  E,z 
  0  e
The group of pairs (E,z) for which (E, z)  1 is defined as the
Gamma Ray Horizon (GRH) (Fazio-Stecker relation).
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Optical Depth & Gamma Ray Horizon
GRH for a specific scenario:
Opaque region
Transparent region
For each source (fixed redshift) the GRH energy (E0) is defined as
the energy on the GRH.
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Optical Depth & Gamma Ray Horizon
Influence of the Cosmological Parameters
dt

dz

1 1  z 
look-back time
H0 1  mz 1  z   z2  z  
2

1
2
•The Hubble constant: H0=724 Km s-1 Mpc-1 (Spergel et al, 2003)
Similar shift (10% at 3Ho) over
the whole redshift range
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Optical Depth & Gamma Ray Horizon
•The cosmological densities:
m=0.290.07, =0.720.09 (Wang et al, 2003)
m

0% variation at z=0
10% and 5 % at z=4
astro-ph-0107582
submited APh
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Optical Depth & Gamma Ray Horizon
MAGIC capability
• We assume an EBL model (Kneiske et al, 2004) and universe
with H0=72 Km s-1 Mpc-1 , m=0.29 and =0.72.
• MAGIC characteristics from MC : Trigger Collection Area,
Energy Threshold and Energy Resolution.
• The suitable -ray candidates:
– Well known TeV emitters (Mkn421, Mkn501 & E1426+428)
– Egret Sources extrapolation
• Flux extrapolation (source model & data, Optical Depth, Culmination
angle, MAGIC, 50h)  Fit to
(E)   0  E  exp(  E E0 )
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Optical Depth & Gamma Ray Horizon
Despite simplification,
reasonable 2 and
 Eo = 1-5%sta  1-5%sys
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Cosmological
Measurements
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Cosmological Measurements
The new method
The GRH energy depends on the Cosmology and the distance to the source 
A cosmological dependent distance estimator, which does not
rely on standard candles.
Moreover, the GRH behaves
differently as a function of
redshift than other
observables already used
for cosmology
measurements.
The GRH can be used
as an independent
method to measure
cosmological parameters
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Cosmological Measurements
m=0.29, =0.72
Four parameters fit based on a multi-dimensional interpolating routine.
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Cosmological Measurements
Statistic Precision for m & 
An external constraint of 724 km/ s Mpc (Spergel et al, 2003) for the
Hubble constant is used.
Expected contour of
68 %, 95% and 99%
confidence level
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Cosmological Measurements
Estimation of foreseen systematic errors
• Systematic error on GRH determination:    s (E)  e (E)
• Global energy scale: 15%
   0  E  e( E E0 )
• Extragalactic Background Light:
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Cosmological Measurements
Estimation of foreseen systematic errors
• Systematic error on GRH determination:    s (E)  e (E)
• Global energy scale: 15%
   0  E  e( E E0 )
• Extragalactic Background Light:
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Cosmological Measurements
Above redshift z0.1, the difference on
the GRH come from UV background.
– Fit only source with z > 0.1
– Add one parameter to fit : UV
background level.
High Correlation
UV-m 
External Constraints:
5,15,25,30 %
(50 %, Scott et al, 2000)
Oscar Blanch Bigas
astro-ph-0406061
submited APh
Seminari IEEC - 15-XII-04
Cosmological Measurements
Comparison to current m and  measurements: galaxy counting,
Supernovae and Microwave.
15 % UV constraint
Oscar Blanch Bigas
30 % UV constraint
Seminari IEEC - 15-XII-04
Conclusions
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04
Conclusions-Outlook
• Precise Measurement of the GRH lead to a new technique to
measure m and 
– Independent from other techniques currently used.
– No standard-candle ( but uniform and isotropic EBL )
– Active Galactic Nuclei  highest observable redshift
• The precision of this technique is dominated by the systematic due
to the poor knowledge of the EBL. At least a 15-25 % precision on
the UV background level is needed (currently 50%).
• MAGIC (as well as other Cherenkov Telescopes) already started to
observe AGNs at large redshift (z>0.1).
How many are going to be seen?
• AGN are interesting by itself but any spectrum from an AGN will
help to get cosmological information with this method.
Oscar Blanch Bigas
Seminari IEEC - 15-XII-04