search of high energy cosmic sources with the plataforma solar de almeria: the graal experiment...
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Search of High Energy Cosmic Sourceswith the Plataforma Solar de Almeria:
The GRAAL Experiment
Fernando ArquerosUniversidad Complutense de Madrid
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
amma-aystronomy at
mería
GRAAL
Allegorical virgin holding the GRAAL in the form of a Photomultiplier
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAAL
F. Arqueros1, J. Ballestrin2, D.M. Borque1, M. Diaz-Trigo3, H.-J. Gebauer3, R. Enriquez1 and R. Plaga3
1Universidad Complutense de Madrid2CIEMAT- PSA 3Max-Planck Institut für Physik
Also collaboration from:
Universidad de AlmeríaUniversidad de Sevilla
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAAL
Interest of Gamma-ray Astronomy in the energy range around 100 GeV.
Ground-based Cherenkov telescopes is a well established technique in the TeV range.
Sensitivity CTs is limited by the mirror size.
ΩΔtεA
S/N
A solar power plant provides the highest available mirrored area.
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAAL
THE SOLAR POWER PLANT TECHNIQUE
Danaher et al. (1982): first proposal
Tumer et al. (1990): secondary optics 1 heliostat 1 PMT
CELESTE and STACEE.
GRAAL follows a different approach.
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAALTHE PLATAFORMA SOLAR DE ALMERIA
PSA is a CIEMAT centre for the research in thermal solar technologies.
Located in the desert of Tabernas southern Spain at 505 m a.s.l. (37 N, 2.4W).
Dark site. Main problem is frequent high humidity.
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAALGENERAL PRICIPLES OF OPERATION
Non-imaging optics.
63 heliostats focus the light onto 4 large Winston cones in the central tower.
Each Winston cone detects light from 13-18 heliostats in one PMT.
Heliostats are identified via different arrival times.
Cent
ral t
ower
Cone 1
Cone 2
Cone 3
Cone 4
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAALTHE HELIOSTAT FIELD CESA – I
Each one consists of 24 facets (heliostat area of 39.6 m2). Beam spread of 0.25 (1 ).
From a total of 225 heliostats, GRAAL uses 63.
Total mirrored are of GRAAL is 2500 m2.
Problem: Dew formation on the mirrors Solution: All mirrors are sprayed every second day with a tensid solution which prevents drop formation.
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
The GRAAL detector is installed in a dedicated enclosure at the 70 m level of the central tower
GRAAL
GRAAL
64 mC1 C3C2C4
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
Let us open the door !
GRAALDirection reconstruction (I)
Direction is inferred from the time pattern of the pulse train. Digital Scope 1 GHz bandwith 500 ps/bin.
Heliostat identification front reconstruction Incoming direction
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAALDirection reconstruction (II)
Cherenkov front is spherical with a radius of about 10 km.
The shower axis is assumed to cross the centre of the field. Angular error related to core position and broadening of the shower extension.
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
Core
GRAALPrecision in the absolute pointing
32 h of Crab data of Feb/March 2000. ON-source (upper) and OFF-source (lower), including unfavorable conditions.
Reconstruction is independent of heliostat pointing
Deviations smaller than 0.05
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAALAngular resolution
Reconstructed direction is independent of the assumed pointing direction
MC simulations give for -rays (z=10 , az=45 ) a resolution of(63) 0.35
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAALEnergy Threshold and Detection Area
Asymptotic detection area of 15000 m2.
MC energy threshold for -rays (250100) GeV
MC trigger rate from cosmic rays background 3 Hz in agreement with real data (2-4 Hz)
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
Effective area vs primary energy for -rays (upper) and protons (lower).
GRAALGRAAL project development
Feb. 99 collaboration agreement with PSA June 99 construction of a new test platform Aug 99 Data acquisition begins Nov 99 Integral trigger in operation Feb. 00 anti-dew spray system in operation Aug 00 remote auto-alarm operational (mobil-phone)
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAALObservation of the Crab nebulae
Angular distance of reconstructed directions from the Crab. Upper) ON (continuous) and OFF (dashed) -source. Lower) ON-OFF (normalized) number of events
ON-OFF (normalized) number of events vs zenith and azimuth distance.
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAAL
7 hours of usable ON-source observing time
Significance of the signal 4.5
No evidence for emission of other sources ( 3C 454.3, 3EG 1835+35)
F. Arqueros et al. (submitted to Astroparticle Physics)
Observation of the Crab nebulae
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAAL
Highest time resolution than any other Cherenkov experiment.
Largest total mirror area of any current detector.
The tower detector is much less complex than other imaging solar Cherenkov Smaller costs, fewer systematic errors. Price = higher NSB and thus a higher energy threshold.
Strengths of GRAAL
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAAL
Field of view restricted to the shower maximum (common to all solar plant experiments)
- It biases the direction reconstruction towards the pointing direction. - It leads to a very similar time structure of the shower front for -rays . and protons.
Thus: /p separation is difficult (still much work to do).
Weather conditions. In GRAAL only 4 % of the time (including both weather and moon light) can be used for taking good data..
Difficulties
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
GRAAL
GRAAL takes data since Aug. 99. Under remote control since Aug. 00
The experiments performs as planned with lower systematic errors than expected.
The restricted field of view destroys the difference between gamma and hadron showers and worsens the angular resolution.
Conclusions
F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001
