Towards Gamma-Ray Astronomy at ultra-high energies

M. R. HAMPEL , E. HOLT, J. HULSMAN, M. JOSEBACHUILI, A. LUCERO, D. MELO, S. MÜLLER , M. PERLIN , M. PLATINO , D. RAVIGNANI, M. RONCORONI, E. SANTOS,; N. GONZÁLEZ, F. SÁNCHEZ, M. ROTH, A. ALMELA , B. ANDRADA, A. BOTTI, A. CANCIO , L. FERREYRO, J. M. FIGUEIRA, A. FUSTER, B. GARCÍA,; C. SARMIENTO-CANO , D. SCHMIDT, G. SILLI , F. SUAREZ, A. TABOADA , O. WAINBERG , B. WUNDHEILER , A. YUSHKOV AND A. ETCHEGOYEN

Encuentro; Pierre Auger Internal GAP Note Nº 2017-050; 2017

The Auger Observatory has a unique possibility of exploring a new branch of Astronomy: Gamma Astronomy at the highest energies. In the search for ultra-high-energy photons, it is crucial to define composition-sensitive parameters capable of adequately rejecting the hadronic background. In this work, we explore the parameter M_b that combines the muon densities measured by the AMIGA buried scintillation detectors and their distance to the shower core, similarly to the well-known observable S_b . We analyze the discrimination power of M_b between photon and proton primaries in the energy range between E_MC = 10^16.5 eV and E_MC = 10^17.5 eV. The aim of this work is to tune M_b to be applied in the 433 m Infill array (AERAlet) whose central station is equipped with aburied scintillation detector. We found that M_b with b = 2 can separate photons from protons via the number of muons in the nearest muon detector with a merit factor of at least ∼5.06 at energies around E_rec = 10^17 eV. By imposing a cut on the value ofM_2 = 0.065, 99.90% of the background (proton) events can be rejected at a 1σ confidence level while keeping 79.8% of the photon events for energies above E_rec = 10^16.5 eV following a realistic spectrum. These are quite encouraging results.