A Search for Photons with Energies Above 2 × 10<sup>17</sup> eV Using Hybrid Data from the Low-Energy Extensions of the Pierre Auger Observatory
P. Abreu, M. Aglietta, Justin M. Albury, I. Allekotte, Kévin Almeida Cheminant, A. Almela, Jaime Álvarez-Muñiz, Rafael Alves Batista, Juan Ammerman Yebra, Gioacchino Alex Anastasi, Luis A. Anchordoqui, B. Andrada, S. Andringa, C. Aramo, P. R. Araújo Ferreira, E. Arnone, Juan Carlos Arteaga Velázquez, H. Asorey, P. Assis, Gael Flores Avila, Emanuele Avocone, Alina Mihaela Badescu, Alena Bakalová, A. Balaceanu, Felicia Barbato, J. A. Bellido, C. Berat, M. E. Bertaina, Gopal Bhatta, Peter L. Biermann, Virginia Binet, K. Bismark, Teresa Bister, Jonathan Biteau, Jiří Blažek, C. Bleve, J. Blümer, M. Boháčová, Denise Boncioli, C. Bonifazi, Luan Bonneau Arbeletche, Nataliia Borodai, Ana Martina Botti, J. Brack, T. Bretz, P. Gabriel Brichetto Orchera, F. L. Briechle, P. Buchholz, A. Bueno, S. Buitink, Mario Buscemi, M. Büsken, K. S. Caballero‐Mora, Lorenzo Caccianiga, Fabrizia Canfora, Ioana Caracas, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, Lorenzo Cazon, M. Cerda, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, A. C. Cobos Cerutti, R. Colalillo, A. Coleman, M. R. Coluccia, R. Conceição, Antonio Condorelli, Giovanni Consolati, F. Contreras, Fabio Convenga, Diego Correia dos Santos, C. E. Covault, S. Dasso, K. Daumiller, B. R. Dawson, J.A. Day, R. M. de Almeida, Joaquín de Jesús, S. J. de Jong, J. R. T. de Mello Neto, I. De Mitri, J. de Oliveira, Danelise de Oliveira Franco, F. de Palma, V. de Souza, Emanuele De Vito, A. Del Popolo, Mariano del Río, O. Deligny, L. Deval, A. di Matteo, M. Dobre, C. Dobrigkeit, Juan Carlos D’Olivo, Luis Miguel Domingues Mendes
Abstract
Abstract Ultra-high-energy photons with energies exceeding 10 17 eV offer a wealth of connections to different aspects of cosmic-ray astrophysics as well as to gamma-ray and neutrino astronomy. The recent observations of photons with energies in the 10 15 eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding 2 × 10 17 eV using about 5.5 yr of hybrid data from the low-energy extensions of the Pierre Auger Observatory. The upper limits on the integral photon flux derived here are the most stringent ones to date in the energy region between 10 17 and 10 18 eV.