Search for First Harmonic Modulation in the Right Ascension Distribution   of Cosmic Rays Detected at the Pierre Auger Observatory
  We present the results of searches for dipolar-type anisotropies in different energy ranges above $2.5\times 10^{17}$ eV with the surface detector array of the Pierre Auger Observatory, reporting on both the phase and the amplitude measurements of the first harmonic modulation in the right-ascension distribution. Upper limits on the amplitudes are obtained, which provide the most stringent bounds at present, being below 2% at 99% $C.L.$ for EeV energies. We also compare our results to those of previous experiments as well as with some theoretical expectations. 
The Pierre Auger Collaboration : P. Abreu, M. Aglietta, E.J. Ahn,   I.F.M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P...
astro-ph.HE