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
2012.07.19
2012.07.19
COSPAR2012 @
1 Mysore, India
PSB.1-0027-12
ICRC2011@Beijing,China HE 1.5 15. Aug
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).
CALET
payload
International Space Station
Dark Matter
annihilation
or decay
Cosmic Ray Sources
e- &
e+
2gamma
Japanese
Experiment
Module (Kibo)
electron
gamma
nucleus
Objectives
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
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
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bCALET Detector
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).
bCALET-1
bCALET-2
Anti
IMC
TASC
Tungsten
bCALET-1
IMC
TASC
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bCALET-2
CALET
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
SΩ
21 cm2sr
320 cm2sr
1200 cm2sr
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The Balloon Flight Observation Summary
bCALET-1
bCALET-2
Date
31, May, 2006
27, Aug, 2009
Place
Sanriku
Taiki
37km
35km
6 hours
(37km level fright: 3.5hours)
4.5 hours
(35km level flight: 2.5hours)
~3000@37km
~12000@35km
Level flight altitude
Duration
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
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Data Analysis
Flight data
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.
1MIP
Electron-triggered
events
Distribution of ADC
counts during muonrun (1 BGO log)
Gamma-triggered
events
Track reconstruction
Energy estimation
Energy estimation
< 6.7GeV
> 6.7GeV
Position correction
The accurate positions
of scintillating fibers
were estimated from
the muon track in IMC.
Example of muon track
reconstruction for
position correction
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Proton rejection
by lateral spread
in TASC and IMC
Proton rejection by lateral
spread in TASC and
shower maximum depth
Correction of
gamma-ray
contaminant
Electron spectrum
COSPAR2012 @ Mysore, India
Correction of
electron
contaminant
Gamma-ray spectrum
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Detector Performance (Monte-Carlo Simulation)
Energy Resolution :
Angular Resolution :
The shower axis was
determined by the least-square
fitting of shower cores in IMC.
electrons
: 1.4 °
gamma-rays : 1.6 °
The incident energy was estimated by the
sum of the deposited energy in TASC.
electrons
: 7.4% (@ 10GeV)
gamma-rays : 6.4% (@ 10GeV)
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.
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Detector Performance (Monte-Carlo Simulation)
Proton rejection power :
We used lateral spread and shower maximum
depth to reject proton background from
electron-like events.
■ High energy electrons (> 6.7 GeV)
correlation map of lateral spread in TASC
and shower maximum depth
parameter1. Lateral spread
electron
proton
concentrated
broad
e retain ： 82.2%
p contami ： 6.1%
parameter2. Shower maximum depth
■ Low energy electrons (< 6.7 GeV)
correlation map of lateral spread in
TASC and energy concentration in IMC
Transition
curve
e remain ： 81.0%
Shower Maximum
p contami :11.6%
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Observed Energy Spectra of Electrons and Gamma-rays
Electron spectrum
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 :
Gamma-ray spectrum
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
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Comparison of Electron Energy Spectrum in 1-100GeV
bCALET-1 (Sanriku, altitude 37km)
Latitude : 39.1°(ΘM=0.525)
Rigidity cutoff : ~13.3GV
bCALET-2 (Taiki, altitude 35km)
Latitude : 42.4°(ΘM=0.583)
Rigidity cutoff : ~11.8GV
secondary
AMS-01 (space, altitude 320-390km)
primary
Rigidity cutoff : ~10.0GV
(when ΘM =0.583)
HEAT (Lynn Lake, altitude 5.7g/cm2)
Latitude : 56.5°(ΘM=0.790)
Rigidity cutoff : ~5.8GV
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.
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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 gammarays were compatible with the former experiments and simulations.
• These prototypes brought enough feedback for development of
CALET.
• Now we aim to the CALET mission !
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.
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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. 21224006).
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