HE Aug 1 Cosmic-ray Electrons and Atmospheric Gamma-rays in 1-30 GeV Observed with Balloon-borne CALET Prototype Detector T. Niita, S. Torii ， S. Ozawa, K. Kasahara ， H. Murakami ， Y. Ueyama ， D. Ito, M. Karube, K. Kondo, M. Kyutan (Waseda Univ.) Y. Akaike (ICRR / Tokyo Univ.) T. Tamura (Kanagawa Univ.) K. Yoshida (Shibaura Institute of Tech.) Y. Katayose (Yokohama National Univ.) Y. Shimizu (Space Environment Utilization Center / JAXA), H. Fuke (Institute of Space and Astronautical Science / JAXA) On behalf of bCALET Team Mysore, India PSB

Mysore, India2 Japanese Experiment Module (Kibo) International Space Station Cosmic Ray Sources Dark Matter annihilation or decay electron gamma nucleus e - & e + 2gamma CALET ~CALorimetric Electron Telescope~ CALET, a detector for high energy cosmic-ray electrons, gamma-rays and nuclei, will be installed on the Japanese Experiment Module Exposed Facility (JEM-EF) of the International Space Station (ISS) in 2014 for long-term observation (2-5 years). bCALET ~Balloon-borne CALET prototype~ We developed balloon-borne payloads to verify CALET capability by carrying out precursor flights for electron and gamma-ray observation. bCALET-1 : 1/12 prototype, observation in May 2006 bCALET-2 : 1/2 prototype, observation in August 2009 Electrons 1GeV-20TeV Nearby sources, Dark matter signatures, Particle transport, Solar physics Gamma-rays 10GeV-10TeV Dark matter signatures, Point sources, Diffuse gamma-rays, Bursts Nuclei 10GeV-1000TeV Particle transport, Acceleration Objectives CALET payload

Mysore, India3 bCALET Detector IMC TASC bCALET-1 Tungsten bCALET-2 bCALET detectors (both bCALET-1 and bCALET-2) have generally the same configuration as CALET, which is composed of an imaging calorimeter (IMC) and a total absorption calorimeter (TASC). IMC TASC Anti bCALET-1bCALET-2CALET IMC 1.3 r.l. (W 4 layers) SciFi 128mm x 4XY layers 3.5 r.l. (W 7 layers) SciFi 256mm x 8XY layers 3.0 r.l. (W 7 layers) SciFi 448mm x 8XY layers TASC 13.4 r.l. (BGO 4 logs x 6 layers) 13.4 r.l. (BGO 10 logs x 6 layers) 27.2 r.l. (PWO 16 logs x 12 layers) Trigger Plastic scintillator (S1, S2) & TASC top layer (BS) Plastic scintillator (S1,S2,Anti) & TASC top layer (BS) IMC dynode & TASC top layer SΩ21 cm 2 sr320 cm 2 sr1200 cm 2 sr

Mysore, India4 The Balloon Flight Observation Summary bCALET-1bCALET-2 Date 31, May, , Aug, 2009 Place SanrikuTaiki Level flight altitude 37km35km Duration 6 hours (37km level fright: 3.5hours) 4.5 hours (35km level flight: 2.5hours) Triggered event number Taiki, Hokkaido Latitude 42.4° Longitude 143.4° Rigidity cutoff 11.8GV Sanriku, Iwate Latitude 39.1° Longitude 141.8° Rigidity cutoff 13.3GV

Mysore, India5 Data Analysis 1MIP Distribution of ADC counts during muon- run (1 BGO log) Calibration by cosmic-ray muons All of the 4096 scintillating fibers and the 60 BGO scintillators were calibrated using muon data taken before the launch. Example of muon track reconstruction for position correction Electron-triggered events Gamma-triggered events Energy estimation Track reconstruction Proton rejection by lateral spread in TASC and IMC < 6.7GeV > 6.7GeV Proton rejection by lateral spread in TASC and shower maximum depth Energy estimation Correction of gamma-ray contaminant Correction of electron contaminant Electron spectrumGamma-ray spectrum Flight data Position correction The accurate positions of scintillating fibers were estimated from the muon track in IMC.

Mysore, India6 Detector Performance (Monte-Carlo Simulation) electrons : 1.4 ° gamma-rays : 1.6 ° Angular Resolution : The shower axis was determined by the least-square fitting of shower cores in IMC. Example of electron track reconstruction (simulation event) Incident direction & Reconstructed shower axis Geometrical condition We selected the events which pass through the top of the detector and the bottom of the third BGO layer so as to retain good energy resolution. Energy Resolution : The incident energy was estimated by the sum of the deposited energy in TASC. electrons : 7.4% 10GeV) gamma-rays : 6.4% 10GeV)

Mysore, India7 e remain ： 81.0% p contami :11.6% e retain ： 82.2% p contami ： 6.1% Detector Performance (Monte-Carlo Simulation) Proton rejection power : We used lateral spread and shower maximum depth to reject proton background from electron-like events. electronproton concentratedbroad Shower Maximum ■ Low energy electrons (< 6.7 GeV) correlation map of lateral spread in TASC and energy concentration in IMC ■ High energy electrons (> 6.7 GeV) correlation map of lateral spread in TASC and shower maximum depth parameter1. Lateral spread parameter2. Shower maximum depth Transition curve

Mysore, India8 Electron spectrum Gamma-ray spectrum Observed Energy Spectra of Electrons and Gamma-rays Simulation by COSMOS v7.49 (1) Primary particles : electron : BETS, PPB-BETS proton, He : AMS-01 C, N, O, Fe : HEAO, ATIC, CRN (2) Solar modulation effect : assume modulation factor Φ as 0.6 GV (3) Geomagnetic cutoff : select the primary particles which can reach the top of the atmosphere under the rigidity cutoff effect (use IGRF2005 as a geomagnetic data) (4) Interaction with atmosphere : use DPMJET3 as a hadron interaction model Observed energy spectra are compatible with simulation

Mysore, India9 Comparison of Electron Energy Spectrum in 1-100GeV primary secondary The primary electron spectrum observed by bCALET is compatible with the results of earlier experiments. The rigidity cutoff effect can be compared with that of AMS-01 spectrum at the similar latitude though there is a slight difference due to the altitude. In the case of the secondary electron spectrum, we should note that bCALET directly observed secondary electrons generated in atmosphere but AMS-01 and PAMELA observed down-going albedo particles. bCALET-1 (Sanriku, altitude 37km) Latitude : 39.1°(Θ M =0.525) Rigidity cutoff : ~13.3GV bCALET-2 (Taiki, altitude 35km) Latitude : 42.4°(Θ M =0.583) Rigidity cutoff : ~11.8GV AMS-01 (space, altitude km) Rigidity cutoff : ~10.0GV (when Θ M =0.583) HEAT (Lynn Lake, altitude 5.7g/cm 2 ) Latitude : 56.5°(Θ M =0.790) Rigidity cutoff : ~5.8GV

Summary A series of balloon experiments with the CALET prototype detector (bCALET) was carried out for verification of the capability and evaluation of the performance. The observed spectra of the electrons and the atmospheric gamma- rays were compatible with the former experiments and simulations. These prototypes brought enough feedback for development of CALET. Now we aim to the CALET mission ! Mysore, India10 We have successfully been developing the CALET instrument for long-term observation of electrons 1GeV-20TeV, gamma-rays 10GeV-10TeV, and nuclei 10GeV-1000TeV at ISS. The launch will be held in 2014 by H-IIB rocket.

Mysore, India11 Acknowledgment We greatly thank the staff of Balloon Team in ISAS for their essential contributions to the successful flight of bCALET. This work is supported by JSPS Grant-in-Aid for Scientific Research S (Grant no ).