Balloon-borne experiment for observation of sub-mev/mev gamma-rays from Crab Nebula using an Electron Tracking Compton Camera

Transcription

1 Balloon-borne experiment for observation of sub-mev/mev gamma-rays from Crab Nebula using an Electron Tracking Compton Camera S. Komura, T. Tanimori, H. Kubo, A.Takada, S. Iwaki, S. Kurosawa, Y. Matsuoka, S. Miyamoto, T. Mizumoto, Y. Mizumura, K. Nakamura, S. Nakamura, M. Oda, J. D. Parker, T. Sawano, S. Sonoda, T. Takemura, D.Tomono (Kyoto Univ.) K. Miuchi (Kobe Univ.) gas-tpc Sub-MeV gamma-ray Imaging SMILE-I (Sep., 2006 ) Loaded-on-balloon Experiment SMILE-I diffuse cosmic / atmospheric γ Pixel Scintillators SMILE-II (now planning) Crab Nebula, Cyg X-1

2 Contents 1. Problems and its causes of MeV astronomy 2. How to challenge by ETCC 3. ETCC for SMILE-II Improvements since SMILE-I Performances Test in high background environment Ability of polarization measurement Summary 40th COSPAR Moscow, 8 August

3 Problems in MeV gamma-ray astronomy COMPTEL 1-30 MeV map Fermi > 1 GeV map ~30 objects/10 years V. Schönfelder+ (A&AS, 2000) ~2000 objects/2 years P. L. Nolan+ (ApJS, 2012) Detection sensitivity Unclearness of image Wide sensitivity gap What is the main cause of these problems? 40th COSPAR Moscow, 8 August

4 Causes of problems Incomplete Compton reconstruction COMPTEL did not use direction of recoil electron. Imaging by superposition of event circles Ghost signals Low S/N ratio COMPTEL 5 May 1991 GRB Ryan, J.M., NewAR, 48, 199 (2004) BG rejection by time of flight Huge Background in space produced by cosmic-ray interactions with detector COMPTEL s BG rejection was not sufficient. ~ 1/10 of the expected sensitivity G. Weidenspointner+ (A&A, 2001) Low BG is most important for MeV observation. 40th COSPAR Moscow, 8 August

5 Track Range [mm] gas-tpc 3D-track & energy Electron Tracking Compton Camera (ETCC) Pixel Scintillators position & energy no use Electron Track 137 Cs 2 m Complete Compton reconstruction detects incident direction of each photon High quality imaging Large Field of View BG rejection ability 1. Particle identification by de/dx 2. Compton kinematical test use Electron Track ETCC has the potential of overcoming the problems in MeV astronomy. de/dx distribution ghost ~ 4 times better S/N 40th COSPAR Moscow, 8 August 2014 Energy [kev] 5

6 ETCC for 2 nd experiment (SMILE-II) SMILE-II Flight model TPC Scinti. Pressure vessel 1 m Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment Gamma-ray Imaging test Observation of Crab > 5σ Improvements Increasing the size of ETCC - 10 x 10 x 15 cm 3 (30 cm) 3 Fort km, several hours Requirements SMILE-I Effective 300 kev > 0.5 cm cm 2 Angular 662 kev < 10 o 20 o ~10 old DAQ new DAQ stopped scattered ~4 cm DAQ optimizing for ETCC ~10 - Tracking eff. : ~10% ~100% - Angular res. : ~ 1 cm 2 SMILE-II ETCC has already satisfied the requirements for Crab detection. 40th COSPAR Moscow, 8 August

7 Effective area Points: measured Lines: simulated 30cm-cubic (new DAQ, Xe 3 atm, 3 radiation length scintillator) 30cm-cubic (new DAQ, Ar 1 atm) 10 cm-cubic (old DAQ, Ar 1 atm) SMILE-III Gas type of TPC Gas pressure R.L. of scinti. SMILE-II Large detector New DAQ SMILE-I type [kev] SMILE-II ETCC ~1 cm 300 kev (requirement > 0.5 cm 2 ) Experiment Simulation (not including detector response) => ETCC obtains ~100 % of Compton events. We will upgrade to SMILE-III ETCC ~10 cm 2 (in 2016) 40th COSPAR Moscow, 8 August

8 Efficiency Other Performance Parameters Large Field of View 137 Cs (662 kev) kev 90 deg. ~ 6 sr Angular resolution 5.3 o 662 kev Energy resolution Limit calculated from Energy & Position res. 18 %@ 166 kev 11 %@ 662 kev 40th COSPAR Moscow, 8 August

9 Detection sensitivity Xe 3 atm, Upgrading scintillators SMILE-II : detectable Crab nebula (Fort 40 km, 4 hours) SMILE-III : 10 times better sensitivity (polar 40 km, 1 month) ~10 celestial objects, extragalactic and galactic plane survey 40th COSPAR Moscow, 8 August

10 Test in high background environment Proton beam Confirmation experiment for gamma-ray detection ability in strong radiation field gamma : neutron = 3 : 1 similar to expected BG at balloon experiment (middle latitude at 35 km altitude) DAQ trigger rate ~ 500 Hz > 5 times stronger than expected SMILE-II DAQ system operated stably. Simulation of SMILE-I BG de/dx distribution gamma e - neutron proton neutron e + p 40th COSPAR Moscow, 8 August

11 Test in high background environment With de/dx selection, BG events are rejected. Spectrum: 662 kev Beam line Raw data BG rejection (de/dx) 662 kev gamma ETCC detected gamma-ray correctly with same efficiency as no beam. ETCC would maintain the sensitivity even in space environment. 40th COSPAR Moscow, 8 August

12 Normalized counts Modulation Factor Ability of polarization measurement (Simulated) 100% linear polarization Modulation Curve (geometry corrected) Energy dependence max Cos θ < 0.7 min Polarization angle 0 deg., 45 deg. High quality Imaging Powerful BG rejection Wide FoV ~ 6 sr Modulation Factor Azimuth angle [deg] = max min max+min Energy [kev] MF > 0.5 (< 400 kev) SMILE-III ~10 cm 2 Crab : 3σ Minimum Detectable Polarization ~ 20 % GRBs : 10-6 erg / cm 2 s (2-3 GRBs / month) ~ 8 % 10-7 erg / cm 2 s (~10 GRBs / month) ~ 30 % 40 km half-day flight polar 40 km 1 month flight 40th COSPAR Moscow, 8 August

13 Normalized counts Normalized counts Ability of polarization measurement (Measured) Experiment in Lab. 133 Ba is set at Φ=90 o 356 kev SMILE-II ETCC Compton scattered ~ 200 kev Fit Eq. A+B sin(2φ+c) (all free) Azimuth angle Φ [deg] Compton effect [kev] scattered gamma on Paraffin is polarized ~ 40 % (by Geant4 simulation) 133 Ba is set at Φ=0 o Signal : BG = 0.03 : 1 ETCC succeed to detect the polarization modulation with low S/N. Azimuth angle Φ[deg] 40th COSPAR Moscow, 8 August

14 Summary ETCC has High contrast imaging Powerful background rejection Wide field of View ~ 6 sr Polarization measurement (simulated MF ~ 0.5 < 400 kev) SMILE-II ETCC ~ 1 cm 300 kev satisfied the requirements for Crab detection (Fort Sumner, 4 hours at 40 km) maintained its sensitivity in high background environment detected the polarization modulation Future Plan: SMILE-III ETCC (~10 times better sensitivity) ~ 10 celestial objects, extragalactic and galactic plane survey (polar region, 1 month at 40 km) Polarization: Crab ~ 20 % (half-day), GRBs (1 month) Thank you for your attention! 40th COSPAR Moscow, 8 August