1. Detection of GRB with Water Cherenkov Detectors
Xavier Bertou
Instituto Balseiro
Denis Allard
University of Chicago

2. Water Cherenkov Detector
EAS Detector
Want uniform answer to incoming particles
Diffuse Cherenkov Cone
Xavier Bertou - RICH Mexico

3. The single Particle Technique
We want to study the high energy (above 100 MeV) component of the GRB spectrum
At these energies, photon showers give only isolated particles at ground level
A GRB would be seen by an EAS array as an increase in background counting rate on the whole array
Xavier Bertou - RICH Mexico

4. Xavier Bertou - RICH 2004 - Mexico
Photon Flux
Photon Showers
Xavier Bertou - RICH Mexico

5. Photon Shower Simulation
250 millions showers generated:
Corsika 6.0
No thinning
50 MeV to 100 GeV
0, 10, 20 and 30° zenith angle
Ground at 1400 m (Auger)
Xavier Bertou - RICH Mexico

6. Auger Mean number is very small
The number of particles decreases with the zenith angle
For the lowest energy showers the probability to reach the ground is very low
Xavier Bertou - RICH Mexico

7. Particles at ground level
Photons dominate:
Cherenkov detectors welcome!
Xavier Bertou - RICH Mexico

8. independent of primary energy!
Secondary spectrum
Secondary spectrum
independent of primary energy!
Photon spectrum
Electron spectrum
Xavier Bertou - RICH Mexico

9. Going to higher altitude
Xavier Bertou - RICH Mexico

10. Altitude/Zenith effect: Overall flux normalization
Xavier Bertou - RICH Mexico

11. Xavier Bertou - RICH 2004 - Mexico
Detector Simulation
we simulated photons and e+e- with SDSim between 1 and 100 MeV and arrival direction between 0 and 60°
Estimation of the probability to detect secondary particles as a function of their nature, energy and arrival direction
Xavier Bertou - RICH Mexico

12. Simple detector trigger
Xavier Bertou - RICH Mexico

13. 90% of detected secondaries are photons
Cherenkov tanks are efficient GRB detectors
Xavier Bertou - RICH Mexico

14. Guetta & Granot ApJ 2003 (=600 t=1s)
Auger
GRB model:
Guetta & Granot ApJ (=600 t=1s)
Xavier Bertou - RICH Mexico

15. What could be done in Auger
Tanks talk to central every second:
Set low threshold and just count
Use 1-fold trigger for low energy particle
Send the count every second to central
At Central:
Moving window of one minute
Look for “n” sigma effect
Currently:
We can apply this method to T2 rates
Only a proof of concept
Xavier Bertou - RICH Mexico

16. Astroparticle Physics: recycling welcome!
Conclusions
Cherenkov tanks are efficient GRB detectors
Auger is at low altitude but it’s big:
Could see something
Easy to implement (and free)
Projects at higher altitude:
4200 m (Puebla)
5200 m (Chacaltaya ?)
Astroparticle Physics: recycling welcome!
Xavier Bertou - RICH Mexico