Cosmology with the New Generation of Cherenkov Telescopes

Seminari IEEC - 15-XII-04Oscar Blanch Bigas

Cosmology with the New Generation of Cherenkov

Telescopes

Oscar Blanch Bigas

IFAE, UAB

Seminari IEEC

15-XII-04


Introduction


INTRODUCTION

• 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, ...

-ray Astronomy


INTRODUCTION

• “Cosmological Principle”: homogeneous and isotropic universe.

Cosmology

2

12222

2

222 dsinrdr

kr

drtRdtds

• In the context of general relativity, the dynamics of the universe is governed by the Friedmann equation.

zzz)z(HHRR

mo 211 222

Where the redshift (z) is defined as: 1+z R0 / R(t) and therefore redshift and time are related by the lookback-time.

2

12

0 211

11

zzzzH

zdzdt

mTime (distance) vs redshift

measures cosmology


The CherenkovTelescopes


The 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).

New Generation of Cherenkov Telescopes

Satellites< 10 GeV

Ground-based> 300 GeV


The Cherenkov TelescopesThe “Big” four

Montosa Canyon,Arizona

Roque de los Muchachos, Canary Islands

Windhoek, Namibia

Woomera, Australia

MAGICMAGIC (2004) (2004)

HESSHESS (2003) (2003)

CANGAROO IIICANGAROO III

VERITASVERITAS


The Cherenkov TelescopesImage Air erenkov Technique

• 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

Alt

itu

de

(Km

)


The Cherenkov Telescopes• The images formed by hadronic showers (background) and electro-

magnetic (signal) are different.

Photons point to the center! Protons do not!


The Cherenkov Telescopes

s appear

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.


The MAGICTelescope


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.

17 m diam

eter

17 m diam

eter

Image Air

Image Air

Cerenkov Telescope

Cerenkov Telescope

@@

Roque de los Muchachos

Roque de los Muchachos


The MAGIC Telescope

• An advanced 17 m Telescope based on a series of innovative features.

A second Generation IACT - MAGIC

17m Ø mirror Ultralight alluminum panels 85%-90% reflectivity

Light carbon fiber tubes65 ton total weightFrame corrected using Active Mirror Control

3.5° FOV camera 577 pixelsOptical fiber analogic

transmission2 level trigger & 300 MHz FADC


The MAGIC TelescopeThe 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)


The MAGIC TelescopeThe 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


The MAGIC TelescopeCamera and signal transmission

577 PMTsCoating & Double crossingInner zone: 396 pixels of 0.1Outer zone: 180 pixels of 0.2

Optical analogic transmitters160 m of fibres: short signal, optically decoupled, cable weigth,...


The MAGIC Telescope


The MAGIC TelescopeSignal 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


The MAGICPhysics


The MAGIC Physics

Dark Matter

Pulsars

GRBs

Quantum Quantum Gravity effectsGravity effects

SNRs

AGNs

-RH & Cosmology


The MAGIC Physics

Active Galactic Nuclei refers to galaxies with a central region where high-energetic processes take place.

Active Galactic Nuclei

• 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, ...


Optical Depth&

Gamma Ray Horizon


Concept - EBL absorption

Optical Depth and GRH

ee

Then the -ray flux is attenuated while travelling from the emission point to the detection point.

The integration over the path travelled across the universe, which depends on the source redshift (z), is the Optical Depth.

zxEzx

dxzd

dtczd)z,E( ,,,,nd

m

z

2

00 2

The group of pairs (E,z) for which is defined as the Gamma Ray Horizon (GRH) (Fazio-Stecker relation).

z,Ee 0

High energy -rays travelling cosmological distances are expected to be absorbed through their interactions with the EBL by:

Optical Depth & Gamma Ray Horizon

1z)(E,



GRH for a specific scenario:

Transparent regionTransparent region

For each source (fixed redshift) the GRH energy (E0) is defined as the energy on the GRH.

source

GRH ener

gy

Opaque regionOpaque region



Influence of the Cosmological Parameters

•The Hubble constant: H0=724 Km s-1 Mpc-1 (Spergel et al, 2003)

2

12

0 211

11

zzzzH

zdzdt

m

look-back time

Similar shift (10% at 3Ho) over

the whole redshift range



•The cosmological densities: m=0.290.07, =0.720.09 (Wang et al, 2003)

0% variation at z=0

10% and 5 % at z=4

m

astro-ph-0107582

submited APh



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

)EEexp(E)E( 00



Despite simplification,

reasonable 2 and

Eo = 1-5%sta 1-5%sys


CosmologicalMeasurements


Cosmological MeasurementsThe 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 usedThe GRH can be usedas an independentas an independentmethod to measuremethod to measure

cosmological parameterscosmological parameters


Cosmological Measurements

m=0.29, =0.72

Four parameters fit based on a multi-dimensional interpolating routine.


Cosmological MeasurementsStatistic Precision for m &

An external constraint of 724 km/ s Mpc (Spergel et al, 2003) for the Hubble constant is used.

Expected contour of

68 %, 95% and 99%

confidence level


Cosmological MeasurementsEstimation of foreseen systematic errors

• Systematic error on GRH determination:

• Global energy scale: 15%

• Extragalactic Background Light:

)EE(eE 00

e )E(s )E(


Cosmological MeasurementsAbove redshift z0.1, 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)

astro-ph-0406061

submited APh


Cosmological MeasurementsComparison to current m and measurements: galaxy counting,

Supernovae and Microwave.

15 % UV constraint 30 % UV constraint


Conclusions


• 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.

Conclusions-Outlook

Cosmology with the New Generation of Cherenkov Telescopes

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