Search for first harmonic modulation in the right ascension distribution of cosmic rays detected at the Pierre Auger Observatory Pierre Auger Collaboration Bueno Villar, Antonio García Gámez, Diego Gascón Bravo, Alberto Lozano Bahílo, Julio Navarro, J. L. Navas Concha, Sergio Zamorano García, Bruno Ultra-high energy cosmic rays Large scale anisotripies Pierre Auger Observatory We present the results of searches for dipolar-type anisotropies in different energy ranges above 2.5 × 1017 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. 2013-11-11T09:30:12Z 2013-11-11T09:30:12Z 2011 preprint Pierre Auger Collaboration. Search for first harmonic modulation in the right ascension distribution of cosmic rays detected at the Pierre Auger Observatory. Astroparticle Physics, 34(8): 627-639 (2011). [http://hdl.handle.net/10481/29088] 0927-6505 doi: 10.1016/j.astropartphys.2010.12.007 arXiv:1103.2721v1 http://hdl.handle.net/10481/29088 eng info:eu-repo/grantAgreement/EC/FP7/220240 http://creativecommons.org/licenses/by-nc-nd/3.0/ open access Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License Elsevier