Wei-Che Hung

DETECTION AND IMAGING OF THE CRAB NEBULA WITH THE NUCLEAR COMPTON TELESCOPE

The Nuclear Compton Telescope (NCT) is a balloon-borne Compton telescope designed for the study of astrophysical sources in the soft gamma-ray regime (200 keV–20 MeV). NCT’s 10 high-purity germanium crossedstrip detectors measure the deposited energies and three-dimensional positions of gamma-ray interactions in the sensitive volume, and this information is used to restrict the initial photon to a circle on the sky using the Compton scatter technique. Thus NCT is able to perform spectroscopy, imaging, and polarization analysis on soft gamma-ray sources. NCT is one of the next generation of Compton telescopes—the so-called compact Compton telescopes (CCTs)—which can achieve effective areas comparable to the Imaging Compton Telescope’s with an instrument that is a fraction of the size. The Crab Nebula was the primary target for the second flight of the NCT instrument, which occurred on 2009 May 17 and 18 in Fort Sumner, New Mexico. Analysis of 29.3 ks of data from the flight reveals an image of the Crab at a significance of 4σ . This is the first reported detection of an astrophysical source by a CCT.

Overview of the Nuclear Compton Telescope

The Nuclear Compton Telescope (NCT) is a balloon-borne telescope designed to study astrophysical sources of nuclear line emission and polarization at soft gamma-ray (0.2-10 MeV) energies. NCT uses high-purity germanium strip detectors for 3D tracking of photon interactions. Compton imaging enables effective background rejection, resulting in a compact but highly efficient instrument. The NCT prototype completed a successful flight from Fort Sumner, New Mexico in 2005. We have since integrated additional detectors, updated the readout electronics, and improved other flight systems. Two flights of the full instrument are upcoming: a conventional flight in New Mexico and a long duration flight from Australia. We give an overview of the instrument and its status prior to the planned balloon flights.

Efficiency and polarimetric calibration of the Nuclear Compton Telescope

The Nuclear Compton Telescope (NCT) is a balloon-borne gamma-ray telescope which uses cross-strip germanium detectors to study astrophysical sources of nuclear line emission. The compact design allows for wide-field imaging with excellent efficiency from 0.2–10 MeV. Moreover, the Compton imaging principle utilized by NCT provides polarimetric sensitivity above 200 keV. We conducted an extensive calibration campaign using radioactive sources prior to our flight from Ft. Sumner, New Mexico in Spring 2009. We present the results of our calibration of the effective area throughout NCTs field of view and compare them with Monte Carlo simulations using a detailed mass model. Additionally, we assess NCTs polarimetric capabilities with observations of a partially-polarized beam.

The Data Readout System of the Nuclear Compton Telescope (NCT)

The Nuclear Compton Telescope (NCT) is a balloon-borne telescope based on the 3D-positioning germanium detectors. It is designed to study astrophysical sources of gamma-ray emission in the energy range of 0.2 MeV to 10 MeV. The data readout system of NCT is designed to amplify, digitize and collect signals from a germanium detector according to a certain trigger scheme. It also has an interface to the NCT flight computer to receive commands and transfer data. This paper contains the design and the scientific test result of the readout system.

The spring 2009 balloon flight of the Nuclear Compton Telescope

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 polarization. NCT consists of twelve high-purity germanium cross-strip detectors (GeDs) that measure both the position and energy of gamma-ray interactions. A 10-GeD version was flown on May 17-18 2009 from the Columbia Scientific Balloon Facility in Fort Sumner, NM, with a total flight duration of 38.5 hours. Here we summarize the instrument, the calibrations, the flight, and our preliminary science results.

Characterizing and Correcting the Cross-Talk Effect on Depth Measurement in the NCT Detectors

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 polarization. The heart of NCT is an array of 12 cross-strip germanium detectors, designed to provide 3D positions for each photon interaction with full 3D position resolution to 1.6 mm3. The x and y positions are provided by the orthogonal strips, and the interaction depth (z position) in the detector is measured to an accuracy of 0.4 mm FWHM using the relative timing of the anode and cathode charge collection signals. The charge collection signals are affected by cross-talk when interactions occur in adjacent strips, altering the timing measurement in those interactions. We simulated this effect in our NCT detectors, and have developed a method to correct the timing information. Here we present the simulation and the correction results.

The 2010 balloon campaign of the Nuclear Compton Telescope

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray telescope. Its compact design uses cross-strip germanium detectors, allowing for wide-field imaging with excellent efficiency from 0.2-10 MeV. Additionally, the Compton imaging principle employed by NCT provides polarimetric sensitivity to several MeV. NCT is optimized for the study of astrophysical sources of nuclear line emission. A ten-detector instrument participated in the 2010 balloon campaign in Alice Springs, Australia, in order to conduct observations of the Galactic Center Region. Unfortunately, a launch accident caused major damage to the payload, and no flight was possible. We discuss the design, calibration, and performance of the instrument as well as prospects for its future.

Ground calibrations of Nuclear Compton Telescope

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 polarization. The heart of NCT is an array of 12 cross-strip germanium detectors, designed to provide 3D positions for each photon interaction with full 3D position resolution to < 2 mm^3. Tracking individual interactions enables Compton imaging, effectively reduces background, and enables the measurement of polarization. The keys to Compton imaging with NCTs detectors are determining the energy deposited in the detector at each strip and tracking the gamma-ray photon interaction within the detector. The 3D positions are provided by the orthogonal X and Y strips, and by determining the interaction depth using the charge collection time difference (CTD) between the anode and cathode. Calibrations of the energy as well as the 3D position of interactions have been completed, and extensive calibration campaigns for the whole system were also conducted using radioactive sources prior to our flights from Ft. Sumner, New Mexico, USA in Spring 2009, and from Alice Springs, Australia in Spring 2010. Here we will present the techniques and results of our ground calibrations so far, and then compare the calibration results of the effective area throughout NCTs field of view with Monte Carlo simulations using a detailed mass model.

Preliminary results from the Spring 2010 balloon campaign of the Nuclear Compton Telescope

The Nuclear Compton Telescope (NCT) is a balloon-borne telescope designed to study astrophysical sources of gammaray emission with high spectral resolution, moderate angular resolution, and novel sensitivity to gamma-ray polarization. The heart of NCT is a compact array of cross-strip germanium detectors allowing for wide-field imaging with excellent efficiency from 0.2-10 MeV. Before 2010, NCT had flown successfully on two conventional balloon flights in Fort Sumner, New Mexico. The third flight was attempted in Spring 2010 from Alice Springs, Australia, but there was a launch accident that caused major payload damage and prohibited a balloon flight. The same system configuration enables us to extend our current results to wider phase space with pre-flight calibrations in 2010 campaign. Here we summarize the design, the performance of instrument, the pre-flight calibrations, and preliminary results we have obtained so far.

Energy, depth calibration, and imaging capability of Nuclear Compton Telescope

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 polarization. The heart of NCT is an array of 12 cross-strip germanium detectors, designed to provide 3D positions for each photon interaction with full 3D position resolution to < 2 mm3. Tracking individual interactions enables Compton imaging, effectively reduces background, and enables the measurement of polarization. The keys to Compton imaging with NCTs detectors are determining the energy deposited in the detector at each strip and tracking the gamma-ray photon interaction within the detector. The 3D positions are provided by the orthogonal X and Y strips, and by determining the interaction depth using the charge collection time difference (CTD) between the anode and cathode. Our preliminary calibrations of the energy and the 3D position of interactions have been completed as well as the verifications of imaging capabilities. Here we will present the techniques and results.