32ND I NTERNATIONAL COSMIC RAY CONFERENCE,BEIJING 2011 The ESAF Reconstruction Framework of UHECR Events for the JEM-EUSO Mission THOMAS MERNIK 1,2 , FRANCESCO FENU 1,2 , DOMENICO D’URSO 3 , ANDREA SANTANGELO 1,2 , KLAUS BITTERMANN 1,2 ,KENJI SHINOZAKI 2 ,MARIO BERTAINA 4 ,SVETLANA BITKEMEROVA 5 ,DMITRY NAUMOV 5 ,GUS- TAVO MEDINA TANCO 6 ON BEHALF OF THE JEM-EUSO COLLABORATION 1 Institut f¨ ur Astronomie und Astrophysik, Kepler Center, Universit¨ at T¨ ubingen, Sand 1, 72076 T¨ ubingen, Germany 2 RIKEN, 2-1 Hirosawa, 351-0198 Wako, Japan 3 Universit` a degli studi di Napoli and INFN Istituto Nazionale Fisica Nucleare, Complesso Universitario di Monte Sant’Angelo - Via Cintia 80126 Napoli, Italy 4 Universit` a degli studi di Torino, Via Pietro Giuria 1 - 10125, Italy 5 JINR, Joliot-Curie 6, 141980 Dubna, Russia 6 UNAM, Ciudad Universitaria, Circuito de la Investigacion Cientifica, Mexico D.F., Mexico mernik@astro.uni-tuebingen.de Abstract: JEM-EUSO is a space based UV detector that will be mounted on the International Space Station (ISS) to monitor the earth’s atmosphere searching for UHECR induced extended air showers (EAS). By evaluating the fluores- cence and Cherenkov signal on the focal surface of the instrument the arrival direction, energy and nature of the primary can be determined. Due to the instantaneous aperture of 10 5 km 2 sr JEM-EUSO will be able to measure several hundreds of events at energies higher than 5*10 19 eV. ESAF is a software for the simulation of space based UHECR detectors. It is configured to cover the specific aspects of the JEM-EUSO mission and to estimate its expected performance. ESAF can simulate every step of the generation and observation of an EAS - from the fluorescence track formation, the light transport in the atmosphere and through the instrument to the telemetry stage. The reconstruction chain covers the dis- crimination of the recorded track from background as well as the estimation of energy, arrival direction and Xmax for the determination of the UHECR species. In this paper we present strategies and algorithms implemented to estimate the spatial and energy resolution of JEM-EUSO as well as a selection of examples demonstrating the expected performance. Keywords: JEM-EUSO, ESAF, Reconstruction, UHECR Events. 1 Introduction The JEM-EUSO detector is a space based UHECR detector designed to be mounted on the Japanese Experiment Mod- ule ”Kibo” on board the ISS [1]. It will monitor the earth’s atmosphere from above to search for extended air showers generated by of cosmic rays in the energy range of 10 19 eV to 10 21 eV and possibly beyond. JEM-EUSO will reach an instantaneous aperture of approximately 10 5 km 2 sr [2] al- lowing a high statistics of events compared to ground based observations. Thus, JEM-EUSO is a key mission to explore the realms of extremely high energy cosmic rays far beyond the capabilities of any ground based UHECR observatory. More details can be found in [3]. ESAF - the EUSO Simulation & Analysis Framework, is a ROOT [4] based, modular software designed to simulate space based UHECR detectors. It has been developed in the context of the former EUSO mission [5]. Its modular structure allows to simulate any EUSO-like 1 instrument. The simulation comprises all physical processes relevant to UHECR measurement. Among these are the development of the resulting air shower, the production of fluorescence and Cherenkov light as well as propagation of photons to- wards the detector. Inside the instrument, simulations in- volve the propagation of photons through the optics, the re- sponse of the photomultiplier and electronics and the event reconstruction eventually. In this article we explain the re- construction algorithms implemented in ESAF and present some results to demonstrate their achievement potentials. 2 The Reconstruction Framework Cosmic ray induced EAS emit fluorescence light isotropi- cally in all directions plus a beamed Cherenkov component. Parts of that light go directly to the telescope. Other com- 1. We define EUSO-like a space borne detector for the mea- surement of UHECR by the measurement of the fluorescence and/or Cherenkov light of EAS. Vol. 3, 120