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)

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)

Outline

1. Introduction

2. NCT Instrument

3. NCT Balloon Campaigns

4. Analysis Pipelines & Science Results

5. Current Status & Summary

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

Introduction – NCT Overview

• 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

balloon gondola

12 GeD array

8 cm

8 cm1.5 cm

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

processed @ LBNL

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)

Introduction – Compton Telescopes (Now/Then)

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

CGRO/COMPTEL• ~40,000 mm3 resolution• E/E ~ 10%• 0.1% efficiency

NCT• ~1 mm3 resolution• E/E ~ 0.2-1%• ~10% efficiency• background rejection• polarization

Over 2 decades of advances in -ray detector technologies beyond those on CGRO

2600 mm

1580 mm

Introduction – Expected Performance of ACT

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

( 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.

D1: 12x12x27 2-mm thick Si (10x10 cm2, 64x64 strips)D2: 12x12x4 16-mm thick Ge (9.2x9.2 cm2, 90x90 strips)

Introduction – Compton Imaging

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

Compton scatter formula:

Back Projection

Image Processing

e.g. List-Mode Maximum Likelihood Expectation Maximization (MLEM)

(Event Reconstruction: S. Boggs. & P. Jean, A&A 2001,)

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

- +Depth

eh

Edge-On View mirror

XY

Z

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

Outline

1. Introduction

2. NCT Instrument 3. NCT Balloon Campaigns

4. Analysis Pipelines & Science Results

5. Current Status & Summary

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

NCT Instrument

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

NCT Instrument

Instrument cradle

Dewar

Cryostat

BGO PMTs

signal cables

Ge detectors

BGO shields

preamps

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

NCT Instrument

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

Power system:

•Solar panels

•Batteries

•Power control unit

NCT Instrument

Pointing and Aspect:•Torque motor•differential GPS•Magnetometer

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

Electronics Bay

Outline

1. Introduction

2. NCT Instrument

3. NCT Balloon Campaigns 4. Analysis Pipelines & Science Results

5. Current Status & Summary

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

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 Ft. Sumner, NM, USA Crab Nebula (o) 22 / (t) 38.5 hrs 10 [7,10,11]

April 29, 2010 Alice Springs, Australia Galactic Center Crashed / (e) 48-96 hrs 10 [7,12,13] Note: * (o) = operational, (t) = total, (e) = expected durations ; ** NCT Taiwan team had not yet attended the collaboration before 2006.

NCT Balloon Campaigns

At float (35-40 km)

2009

2005 2010

Outline

1. Introduction

2. NCT Instrument

3. NCT Balloon Campaigns

4. Analysis Pipelines & Science Results 5. Current Status & Summary

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

NCT – Analysis Pipeline

Raw Data Simulation Data

Detector Effects Engine

Event Reconstruction

Image Reconstruction

Event CalibrationADC to Energy

Strip Pairing

Depth calculation

Strips: ADC, time

MEGAlib(Zoglauer et al., 2006)-Cosima-Revan-Mimrec

Cosima file

Strips: ADC, time

Hits: energy, (x,y,z)

Compton cones

Etc.

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

NCT Results – Ground Calibrations

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

|ΔE| < 1.4σ, CSL:3-7

All strips at 60 keVD8 Positive side D8 Negative side

(179.3 ± 2.2° , Π = 41.2 ± 3.6%)(5m, ~12° separation, 20 iterations)

Effective Area vs. Modified Zenith

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

-40 -30 -20 -10 0 10 20 30 40 50 60 70 80

Modified Zenith (degree)

Effec

tive

Are

a (S

elec

tion-

2) (c

m̂2)

0662-keV [dat]

1173-keV [dat]

1333-keV [dat]

0662-keV [sim]

1173-keV [sim]

1333-keV [sim]

(Chiu 2009)

(Chiu 2010)

(Bellm 2009)

(Simulated)|ΔE| < 1.4σ, CSL:2-7

All strips at 662 keVDepth distribution of D6

Data Simulation

Energy Depth

Efficiency

Polarization

Imaging

NCT Results – Image of Crab Nebula (ep.02)

The first reported detection of an astrophysical source by a CCTJ.-L. Chiu (Institute of Astronomy, NTHU)

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.

(M. Bandstra, ApJ 738, 2010)

NCT Results – Flight Spectrum

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

<Simulation:>Spectral lines from

atmospheric neutrons & protons correspond to most

lines from data.

< 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.

<Simulation:>More counts (~1.5x) in

low-energy part

<Simulation:>Lower counts (<0.5x)

from 511-keV line.

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 vs. Data

Line-identification

(Simulation consulting J. D. Bowen, 2009, N. Gehrels,1985)

Outline

1. Introduction

2. NCT Instrument

3. NCT Balloon Campaigns

4. Analysis Pipelines & Science Results

5. Current Status & Summary

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

• 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

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

• 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.

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 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)

To Be Continued…