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 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( )

3. Analysis Pipelines & Science Results Current Status & Summary
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: 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:
~ keV
Angular resolution:
~5º 662 keV
Field of view: ~π
12 GeD array
8 cm
1.5 cm
8 cm
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) 6

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 )
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 + Z X
Depth Y
J.-L. Chiu (Institute of Astronomy, NTHU)

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

16. 2005 2010 2009 NCT Balloon Campaigns At float Launch Date
(35-40 km)
2009
Launch Date
Launch Location
Primary Target
Duration *
GeDs
References
June 01, 2005
Ft. Sumner, NM, USA
Background
(o) 5.5 / (t) 8.5 hrs 2
[8,9] **
May 17, 2009
Crab Nebula
(o) 22 / (t) 38.5 hrs 10
[7,10,11]
April 29, 2010
Alice Springs, Australia
Galactic Center
Crashed / (e) hrs
[7,12,13]
Note: * (o) = operational, (t) = total, (e) = expected durations ; ** NCT Taiwan team had not yet attended the collaboration before 2006.

17. Analysis Pipelines & Science Results
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
(5m, ~12° separation, 20 iterations)
(179.3 ± 2.2° , Π = 41.2 ± 3.6%)
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 calibrations need 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. Current Status & Summary
Outline
Introduction
NCT Instrument
NCT Balloon Campaigns
Analysis Pipelines & Science Results
Current Status & Summary
J.-L. Chiu (Institute of Astronomy, NTHU)

23. NCT - Current Status of the Project
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, 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 ( ).
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?)
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-designed Ge detector array to study astrophysical sources of nuclear line emission and gamma-ray polarization in 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…