1. SIERRA NEGRA Observatory H. Salazar, C. Alvarez, O.Martinez,T. Murrieta, G.Perez, L.Villasenor, Facultad de Ciencias Físico Matemáticas BUAP

4. CABAÑA ALT: 4560 N 18° 59’ 03.9’’ W 97° 18’ 44.7’’ ALT: 4558 N 18° 59’ 04.6’’ W 97° 18’ 45.4’’ CENTRO ALT: 4557 N 18° 59’ 03.7’’ W 97° 18’ 45.5’’ ALT: 4557 N 18° 59’ 04’’ W 97° 18’ 46.4’’ ALT: 4558 N 18° 59’ 02.9’’ W 97° 18’ 45.2’’ ARENA RAMPA NORTE SUR Array distribution

7. Stability of the detectors: Left one day. Rigth 8 hours Below 1hr.

15. Vertical Muon signals

19. Calibration with the Crab Nebula Flux: 2.68x10 -7 fotons/m 2 /s E>TeV 4 hours observation/day (+-30 o ) =14400 s Area=500 m 2 Flux/day = 1 fotón/day Measured Flux at la Sierra Negra 300 Showers/min 95% protones rejected, 50% photons Direction accuracy +/- 2 o =16 min Showers in the field of view N~240, sigma~15 5 sigma = 75 means 150 days of detection of the Crab.