The Compton Spectrometer and Imager (COSI) is a compact Compton telescope which is inherently sensitive to gamma-ray polarization in the energy range of 0.2-2.0 MeV. A long duration gamma-ray burst, GRB 160530A, was detected by COSI during its 2016 COSI’s balloon flight. The polarization of GRB 160530A was constrained based on the distribution of azimuthal scattering angles from each incident photon inside COSI’s germanium detector array.1 In order to determine COSI’s polarization response and to identify systematic deviations from an ideal sinusoidal modulation, the polarization performance of COSI was validated in the laboratory prior to the 2016. A partially polarized beam was created by scattered emission from a radioactive source off a scintillator. In addition, measurements and simulations of unpolarized radioactive sources were compared to validate our capability of capturing the instrument systematics in the simulations. No statistically significant differences exist between the measured and simulated modulations and polarization angle, where the upper bound on the systematic error is 3%-4%.2 In this talk, I will present the measurements used to validate COSI’s polarimetric performance. Furthermore, I will use these results to estimate the minimum detectable polarization levels for current and future COSI missions.
The Compton Spectrometer and Imager (COSI) is a medium energy gamma ray (0.2 - 10 MeV) imager designed to observe high-energy processes in the universe from a high altitude balloon platform. At its core, COSI is comprised of twelve high purity germanium double sided strip detectors which measure particle interaction energies and locations with high precision. This manuscript focuses on the positional calibrations of the COSI detectors. The interaction depth in a detector is inferred from the charge collection time difference between the two sides of the detector. We outline our previous approach to this depth calibration and also describe a new approach we have recently developed. Two dimensional localization of interactions along the faces of the detector (x and y) is straightforward, as the location of the triggering strips is simply used. However, we describe a possible technique to improve the x/y position resolution beyond the detector strip pitch of 2 mm. With the current positional calibrations, COSI achieves an angular resolution of 5.6 ± 0.1 degrees at 662 keV, close to our expectations from simulations.
The Compton Spectrometer and Imager (COSI) is a balloon-borne soft gamma-ray (0.2-5 MeV) telescope designed to perform wide-field imaging, high-resolution spectroscopy, and novel polarization measurements of astrophysical sources. COSI employs a compact Compton telescope design, utilizing 12 cross-strip germanium detectors to track the path of incident photons, where position and energy deposits from Compton interactions allow for a reconstruction of the source position in the sky, an inherent measure of the linear polarization, and significant background reduction. The instrument has recently been rebuilt with an updated and optimized design; the polarization sensitivity and effective area have increased due to a change in detector configuration, and the new lightweight gondola is suited to fly on ultra-long duration flights with the addition of a mechanical cryocooler system. COSI is planning to launch from the Long Duration Balloon site at McMurdo Station, Antarctica, in December 2014, where our primary science goal will be to measure gamma-ray burst (GRB) polarization. In preparation for the 2014 campaign, we have performed preliminary calibrations of the energy and 3-D position of interactions within the detector, and simulations of the angular resolution and detector efficiency of the integrated instrument. In this paper we will present the science goals for the 2014 COSI campaign and the techniques and results of the preliminary calibrations.
The Nuclear Compton Telescope (NCT) is a balloon-borne soft γ-ray (0.2-10 MeV) telescope designed to perform
wide-field imaging, high-resolution spectroscopy, and novel polarization analysis of astrophysical sources. NCT
employs a novel Compton telescope design, utilizing 12 high spectral resolution germanium detectors, with the
ability to localize photon interaction in three dimensions. NCT underwent its first science flight from Fort
Sumner, NM in Spring 2009, and was partially destroyed during a second launch attempt from Alice Spring,
Australia in Spring 2010. We have begun the rebuilding process and are using this as an opportunity to update
and optimize various aspects of NCT. The cryostat which houses the 12 germanium detectors is being redesigned
so as to accommodate the detectors in a new configuration, which will increase the effective area and improve the
on-axis performance as well as polarization sensitivity of NCT. We will be replacing the liquid nitrogen detector
cooling system with a cryocooler system which will allow for long duration flights. Various structural changes
to NCT, such as the use of an all new gondola, will affect the physical layout of the electronics and instrument
subsystems. We expect to return to flight readiness by Fall 2013, at which point we will recommence science
flights. We will discuss science goals for the rebuilt NCT as well as proposed flight campaigns.
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.
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.
KEYWORDS: Calibration, Sensors, Telescopes, Space telescopes, Monte Carlo methods, Gamma radiation, Germanium, Data conversion, 3D metrology, Polarization
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 NCT's 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 NCT's field of view with Monte Carlo simulations using a detailed
mass model.
I. Chun Shih, Alain Doressoundiram, Yannick Boissel, Françoise Roques, Frederic Dauny, Paul Felenbok, Andree Fernandez, Jean Guerin, Hsiang Kuang Chang, Chih-Yuan Liu
MIOSOTYS is a multiple-object, high-speed photometer. It is currently operating on the 1.93m telescope at
Observatoire de Haute-Provence (OHP), France. The instrument consists of a multi-fibre positioner which can
access maximum 29 targets simultaneously, and an EMCCD camera which is capable of recording low-level light
at high frame rate. This paper will describes the instrument's specifications as well as the performance, i.e.,
signal-to-noise ratio, under the current configuration (ProEM CCD + 1.93m telescope).
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