康卜吞成像光譜儀: 任務與蟹狀星雲的偵測

The Nuclear Compton Telescope (NCT): The Mission and the Crab Nebula Detection

丘政倫(Jeng-Lun Chiu)

指導教授 ： 張祥光

國立清華大學/理學院/物理學系/博士(2010年)

https://doi.org/10.6843/NTHU.2010.00334

摘要

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray (0.2-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and gamma-ray polarization. The heart of NCT is an array of 12 cross-strip germanium detectors (GeDs), providing high spectral resolution (~0.3-0.9% FWHM at 662 keV for most channels) and capability of tracking each photon interaction with full 3D position resolution to 2 mm3. The determined energy and position of interactions in NCT allow Compton imaging, which effectively reduces background and provides polarimetric sensitivity, at moderate angular resolution (~5° FWHM ARM) through event reconstruction. The entire set of detectors and their cryostat are enclosed inside a well of anticoincidence BGO shield, giving an overall field of view (FOV) of ~3.2 sr. The instrument is mounted in a pointed, autonomous balloon platform (gondola).

Before 2010, NCT had flown successfully on two conventional balloon flights in Fort Sumner, New Mexico. The first was a 6-hour prototype flight with two-GeDs at float altitude (~40 km) on June 1, 2005. It succeeded in measuring the soft gamma-ray atmospheric background and the galactic anti-center region. The second flight with 10-GeDs (Fig. 1 right) was launched on May 17, 2009. The total duration was ~38.5 hours with nine of the ten detectors operational for a total of 22 hours at about 35 km to 40 km altitude. The primary science goal was to observe the Crab Nebula and Pulsar. The science instrument performed well during the flight, except for anomalies from the azimuthal pointing system on the first day and from power system on the second. Minor damage of the instrument upon landing made a subsequent flight possible in a short time. The third flight with the same ten-detector instrument was attempted in spring 2010 from Alice Springs, Australia, as NCT’s first southern-hemisphere flight to conduct observations of the Galactic Center Region. However, there was a launch accident that caused major payload damage and prohibited a balloon flight.

NCT is a joint effort of several institutions in Taiwan and in the US. This thesis mainly focuses on the NCT 2009 balloon-flight mission, the ground calibrations, and the detection of the Crab Nebula, in which the author played a major role.

關鍵字

天文物理 ； 鍺偵測器 ； 康卜吞 ； 成像 ； 光譜

參考文獻

[1] Agostinelli, S. et al., "GEANT4 - a simulation toolkit”, Nuclear Instruments and Methods in Physics Research Section A 506, 250-303 (2003).

[3] Amman, M. and Luke, P. N., “Three-dimensional position sensing and field shaping in orthogonal-strip germanium gamma-ray detectors,” Nuclear Instruments and Methods in Physics Research A 452, 155–166 (September 2000).

[4] Amman, M., Luke, P. N., and Boggs, S. E., “Amorphous-semiconductor-contact germanium-based detectors for gamma-ray imaging and spectroscopy,” Nuclear Instruments and Methods in Physics Research A 579, 886–890 (September 2007).

[6] Amrose, S., Boggs, S. E., Coburn, W., Lin, R. P., and Smith, D. M., “Calibration of 3D position in a Ge cross-strip detector,” Nucl. Instrum. Meth. Phys. Res. A 505, 170–173 (2003).

[7] Arons, J., “Pair creation above pulsar polar caps – geometrical structure and energetics of slot gaps,” ApJ 266, 215–241, 1983.