  The ``Gamma Ray Astronomy at ALmeria'' (GRAAL) experiment uses 63
heliostat-mirrors with a total mirror area of ~ 2500 m2 from the CESA-1 field
at the ``Plataforma Solar de Almeria'' (PSA) to collect Cherenkov light from
air showers. The detector is located in a central solar tower and detects
photon-induced showers with an energy threshold of 250 +- 110 GeV and an
asymptotic effective detection area of about 15000 m2. A comparison between the
results of detailed Monte-Carlo simulations and data is presented. Data sets
taken in the period September 1999 - September 2000 in the direction of the
Crab pulsar, the active galaxy 3C 454.3, the unidentified gamma-ray source 3EG
1835+35 and a ``pseudo source'' were analyzed for high energy gamma-ray
emission.Evidence for a gamma-ray flux from the Crab pulsar with an integral
flux of 2.2 +- 0.4 (stat) ^+1.7_-1.3 (syst) x 10^-9 cm^-2 sec^-1 above
threshold and a significance of 4.5 sigma in a total measuring time of 7 hours
and 10 minutes on source was found. No evidence for emission from the other
sources was found. Some difficulties with the use of heliostat fields for
gamma-ray astronomy are pointed out. In particular the effect of field-of-view
restricted to the central part of a detected air shower on the lateral
distribution and timing properties of Cherenkov light are discussed. Upon
restriction the spread of the timing front of proton induced showers sharply
decreases and the reconstructed direction becomes biased towards the pointing
direction. This is shown to make efficient gamma-hadron separation difficult.

Astrophysics