1. Search of High Energy Cosmic Sources with the Plataforma Solar de Almeria: The GRAAL Experiment Fernando Arqueros Universidad Complutense de Madrid F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001

2. amma- ay stronomy at mería GRAALGRAAL Allegorical virgin holding the GRAAL in the form of a Photomultiplier F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001

3. GRAAL F. Arqueros 1, J. Ballestrin 2, D.M. Borque 1, M. Diaz-Trigo 3, H.-J. Gebauer 3, R. Enriquez 1 and R. Plaga 3 1 Universidad Complutense de Madrid 2 CIEMAT- PSA 3 Max-Planck Institut für Physik Also collaboration from: Universidad de Almería Universidad de Sevilla F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001

4. 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.  A solar power plant provides the highest available mirrored area. F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001

5. 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

6. GRAAL THE 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

7. GRAAL GENERAL 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. Central tower Cone 1 Cone 2 Cone 3 Cone 4 F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001

10. GRAAL THE HELIOSTAT FIELD CESA – I  Each one consists of 24 facets (heliostat area of 39.6 m 2 ). Beam spread of 0.25  (1  ).  From a total of 225 heliostats, GRAAL uses 63.  Total mirrored are of GRAAL is 2500 m 2. 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

11.  The GRAAL detector is installed in a dedicated enclosure at the 70 m level of the central tower GRAAL

12. 64 m C1C3C2 C4 F. Arqueros. Multifrecuency Behaviour of High Energy Cosmic Sources. Frascati Workshop 2001 Let us open the door !

13. GRAAL Direction 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

14. GRAAL Direction 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

15. GRAAL Precision 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

16. GRAAL Angular 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

17. GRAAL Energy Threshold and Detection Area  Asymptotic detection area of  15000 m 2.  MC energy threshold for  -rays (250  100) 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).

18. GRAAL GRAAL 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

19. GRAAL Observation 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

20. 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

21. 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

22. 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

23. 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