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 x 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. (C) 2011 Elsevier B.V. All rights reserved. RI Caramete, Laurentiu/C-2328-2011; Dutan, Ioana/C-2337-2011; Aramo, Carla/D-4317-2011; Beatty, James/D-9310-2011; Pesce, Roberto/G-5791-2011; Kemp, Ernesto/H-1502-2011; Chiavassa, Andrea/A-7597-2012; Verzi, Valerio/B-1149-2012; Chinellato, Carola Dobrigkeit /F-2540-2011; Fauth, Anderson/F-9570-2012; Todero Peixoto, Carlos Jose/G-3873-2012; de souza, Vitor/D-1381-2012; Shellard, Ronald/G-4825-2012; Petrolini, Alessandro/H-3782-2011; Albuquerque, Ivone/H-4645-2012; Muller, Marcio Aparecido/H-9112-2012; D'Urso, Domenico/I-5325-2012; Bleve, Carla/J-2521-2012; martello, daniele/J-3131-2012; Valino, Ines/J-8324-2012; Brogueira, Pedro/K-3868-2012; Chinellato, Jose Augusto/I-7972-2012; Falcke, Heino/H-5262-2012; Ebr, Jan/H-8319-2012; Anjos, Joao/C-8335-2013; Sarkar, Subir/G-5978-2011 OI Shellard, Ronald/0000-0002-2983-1815; D'Urso, Domenico/0000-0002-8215-4542; Brogueira, Pedro/0000-0001-6069-4073; Falcke, Heino/0000-0002-2526-6724; Ebr, Jan/0000-0001-8807-6162; Sarkar, Subir/0000-0002-3542-858X

We present the results of searches for dipolar-type anisotropies in different energy ranges above 2.5 x 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. (C) 2011 Elsevier B.V. All rights reserved.