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The Nuclear Compton Telescope (NCT) - 康卜吞成像光譜儀 -

The Nuclear Compton Telescope (NCT) - 康卜吞成像光譜儀 -. 丘政倫 (Jeng-Lun (Alan) Chiu) Institute of Astronomy, NTHU 2011/11/26 ATITC @ Sun Moon Lake Teachers’ Hostel. The NCT’09 Team. S.E. Boggs , C.B. Wunderer, A. Zoglauer, M. Bandstra, E. Bellm, D. Perez-Becker, ( UCB/SSL, USA )

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The Nuclear Compton Telescope (NCT) - 康卜吞成像光譜儀 -

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  1. The Nuclear Compton Telescope (NCT) - 康卜吞成像光譜儀 - 丘政倫(Jeng-Lun (Alan) Chiu) Institute of Astronomy, NTHU 2011/11/26 ATITC @ Sun Moon Lake Teachers’ Hostel

  2. The NCT’09 Team S.E. Boggs, C.B. Wunderer, A. Zoglauer, M. Bandstra, E. Bellm, D. Perez-Becker, (UCB/SSL, USA) H.-K. Chang, J.-L. Chiu, J.-S. Liang (NTHU, Taiwan) Y.-H. Chang, Z.-K. Liu, W.-C. Hung (NCU, Taiwan), C.-H. Lin (Academia Sinica, Taiwan), A. Huang, R.-S. Run(NUU, Taiwan), M. Amman, P. N. Luke (LBNL, USA) P. Jean (CESR, France) Supported by grants from NASA and NSPO(2006-2010)

  3. Outline • Introduction • NCT Instrument • NCT Balloon Campaigns • Analysis Pipelines & Science Results • Current Status & Summary J.-L. Chiu (Institute of Astronomy, NTHU)

  4. Introduction – NCT Overview balloon gondola • Balloon-borne gamma-ray telescope • prototype for future space mission • Energy range: 0.2-10 MeV • Uses Compton scattering • need position and energy information • Compact Ge cross-strip detector array • 37 strips × 2 sides × 12 detector • Anticoincidence BGO shields • Single-strip energy resolution: ~2-4 keV@ 662 keV • Angular resolution: ~5º FWHM @ 662 keV • Field of view: ~π 12 GeD array 8 cm 1.5 cm 8 cm processed @ LBNL J.-L. Chiu (Institute of Astronomy, NTHU)

  5. Introduction – Major Science Goals • Nuclear Line Emission • Positron astrophysics  Annihilation line (511 keV) from galactic center • Supernova gamma-ray lines  26Al (1809 keV), 60Fe (1173,1333 keV), 44Ti (1157 keV) • Polarization Measurements • Pulsars Discriminating models of gamma-ray emission  Polar cap, outer gap, slot-gap… • GRBs How does the inner engine work and what are the γ-ray emission processes?  Understanding the production of the prompt gamma-ray emission: The nature of the jets and the role of magnetic fields. COMPTEL 26Al all-sky map J.-L. Chiu (Institute of Astronomy, NTHU)

  6. Introduction – Compton Telescopes (Now/Then) Over 2 decades of advances in g-ray detector technologies beyond those on CGRO 2600 mm 1580 mm • NCT • ~1 mm3 resolution • DE/E ~ 0.2-1% • ~10% efficiency • background rejection • polarization • CGRO/COMPTEL • ~40,000 mm3 resolution • DE/E ~ 10% • 0.1% efficiency J.-L. Chiu (Institute of Astronomy, NTHU)

  7. Introduction – Expected Performance of ACT D1: 12x12x27 2-mm thick Si (10x10 cm2, 64x64 strips) D2: 12x12x4 16-mm thick Ge (9.2x9.2 cm2, 90x90 strips) ( Boggs et al. 2006 ) The expected sensitivity of the Advanced Compton Telescope (ACT), a proposed space-borne compact Compton telescope. Equivalent sensitivities of COMPTEL (for 106 seconds and the entire mission lifetime) and SPI (for 106 seconds) are shown for comparison. There is a large improvement in using compact Compton telescopes instead of classical Compton or indirect-imaging designs. Various line sources are labeled, suggesting many possible discoveries for ACT. J.-L. Chiu (Institute of Astronomy, NTHU)

  8. Introduction – Compton Imaging Back Projection Image Processing Compton scatter formula: e.g. List-Mode Maximum Likelihood Expectation Maximization (MLEM) (Event Reconstruction: S. Boggs. & P. Jean, A&A 2001,) J.-L. Chiu (Institute of Astronomy, NTHU)

  9. Introduction – Energy & Position Measurements • Energy measurement: Unipolar shaper, 6μs time-to-peak • Timing measurement: bipolar shaper, 170ns • X and Y positions: determined by orthogonal strips  Strip pitch: 2 mm (0.25 mm gap) • Z position:calculated by time difference between X & Y strips  Preliminary (depth) resolution: 0.6 mm Edge-On View mirror h e - + X Z Depth Y J.-L. Chiu (Institute of Astronomy, NTHU)

  10. Outline • Introduction • NCT Instrument • NCT Balloon Campaigns • Analysis Pipelines & Science Results • Current Status & Summary J.-L. Chiu (Institute of Astronomy, NTHU)

  11. NCT Instrument J.-L. Chiu (Institute of Astronomy, NTHU)

  12. NCT Instrument Instrument cradle Dewar Cryostat BGO PMTs preamps signal cables BGO shields Ge detectors J.-L. Chiu (Institute of Astronomy, NTHU)

  13. NCT Instrument J.-L. Chiu (Institute of Astronomy, NTHU)

  14. NCT Instrument Electronics Bay • Pointing and Aspect: • Torque motor • differential GPS • Magnetometer • Power system: • Solar panels • Batteries • Power control unit J.-L. Chiu (Institute of Astronomy, NTHU)

  15. Outline • Introduction • NCT Instrument • NCT Balloon Campaigns • Analysis Pipelines & Science Results • Current Status & Summary J.-L. Chiu (Institute of Astronomy, NTHU)

  16. NCT Balloon Campaigns 2010 2005 At float (35-40 km) 2009

  17. Outline • Introduction • NCT Instrument • NCT Balloon Campaigns • Analysis Pipelines & Science Results • Current Status & Summary J.-L. Chiu (Institute of Astronomy, NTHU)

  18. NCT – Analysis Pipeline Simulation Data Raw Data Cosima file Detector Effects Engine Strips: ADC, time Strips: ADC, time Event Calibration ADC to Energy MEGAlib (Zoglauer et al., 2006) -Cosima -Revan -Mimrec Strip Pairing Depth calculation Etc. Hits: energy, (x,y,z) Event Reconstruction Compton cones Image Reconstruction J.-L. Chiu (Institute of Astronomy, NTHU)

  19. NCT Results – Ground Calibrations Depth distribution of D6 D8 Positive side D8 Negative side All strips at 60 keV All strips at 662 keV Data Simulation Energy Depth (Simulated) |ΔE| < 1.4σ, CSL:2-7 (Chiu 2009) (Chiu 2010) (Bellm 2009) Efficiency Imaging |ΔE| < 1.4σ, CSL:3-7 Polarization (179.3 ± 2.2° , Π = 41.2 ± 3.6%) (5m, ~12° separation, 20 iterations) J.-L. Chiu (Institute of Astronomy, NTHU)

  20. NCT Results – Image of Crab Nebula (ep.02) 1.The Crab was detected at a significance of at least 4σ by NCT during the 2009 balloon flight. 2.Using image processing, the Crab appears in a Compton image made from the data. 3.Examination of the spectrum and ARM histograms from the source are consistent with the simulations of the Crab. 4.This result is the first significant detection of a celestial source by a CCT and is an important step in establishing the viability of the compact Compton telescope design for future space-based wide-survey instruments. The first reported detection of an astrophysical source by a CCT (M. Bandstra, ApJ 738, 2010) J.-L. Chiu (Institute of Astronomy, NTHU)

  21. NCT Results – Flight Spectrum < Discussion > 1.Simulation model, which was built couple decades ago, need to be verified. 2.More background data from NCT flight (i.e. in other epochs) and calibrationsneed to be analyzed. 3.NCT data may help to build a better model for future balloon experiments. Line-identification <Simulation:> Spectral lines from atmospheric neutrons & protons correspond to most lines from data. 1. Spectral lines were fit and identified. 2. Obvious 511-keV line (FWHM=7.5 keV). 3.The rest of spectral lines were mainly related to the activation. <Simulation:> More counts (~1.5x) in low-energy part <Simulation:> Lower counts (<0.5x) from 511-keV line. Simulation vs. Data (Simulation consulting J. D. Bowen, 2009, N. Gehrels,1985) J.-L. Chiu (Institute of Astronomy, NTHU)

  22. Outline • Introduction • NCT Instrument • NCT Balloon Campaigns • Analysis Pipelines & Science Results • Current Status & Summary J.-L. Chiu (Institute of Astronomy, NTHU)

  23. Functionality tests were carried out to verify the status of the GeDs (ps. some need reprocessing), the BGO shields (ps. need further test for 4 of the 36 channels), and the readout electronics (ps. working fine, need minor replacements). A two volume set of investigation report was published by NASA on October 22, 2010. Several recommendations were made to the Balloon Program Office about the standard operating process, where some parts are arguable. More details can be checked in the report online ( http://www.nasa.gov/centers/goddard/business/foia/balloon_mishap.html). Preparing for the rebuild in UCB-SSL: cryocooler, preamp boards, cables, connectors, a couple of new detectors. Rebuild plan in Taiwan side: continued support for readout electronics, development of low-energy coded mask, building a new shield. (ASICS?) NCT - Current Status of the Project • The instrument is planned to be reconstructed with a new configuration(2x2x3), which will enhance the efficiency of polarization measurement and hard X-ray imaging (with a coded mask on top). • The next balloon launch is planned for Spring 2013. J.-L. Chiu (Institute of Astronomy, NTHU)

  24. Summary • NCT is a balloon-borne gamma-ray telescope with compact-designedGe detector array to study astrophysical sources of nuclear line emission and gamma-ray polarizationin 0.2-10 MeV • Tracking capability enables the imaging and polarization measurement. • System worked fine in first two balloon flights, and analysis tools for both experiment and simulation data were well developed. • Intensive ground calibrations from NCT’09/NCT’10 have been carried out and analyzed to provide us better ideas about detector responses. • The Crab Nebula was detected at a significance of 4σ, and it’s the first reported detection of an astrophysical source by a CCT. • Background spectrum at float was surveyed with the spectral-line identification and compared with simulation results on major components. Background throughout NCT’09 is being analyzed. • The instrument is planed to be reconstructed within two years for another flight in Spring 2013. J.-L. Chiu (Institute of Astronomy, NTHU)

  25. To Be Continued…

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