David Hanna

Canadian Hydrogen Intensity Mapping Experiment (CHIME) pathfinder

A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping Experiment) is currently being commissioned at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical interferometer designed to measure the large scale neutral hydrogen power spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used to measure the baryon acoustic oscillation (BAO) scale across this poorly probed redshift range where dark energy becomes a significant contributor to the evolution of the Universe. The instrument revives the cylinder design in radio astronomy with a wide field survey as a primary goal. Modern low-noise amplifiers and digital processing remove the necessity for the analog beam forming that characterized previous designs. The Pathfinder consists of two cylinders 37m long by 20m wide oriented north-south for a total collecting area of 1,500 square meters. The cylinders are stationary with no moving parts, and form a transit instrument with an instantaneous field of view of ~100 degrees by 1-2 degrees. Each CHIME Pathfinder cylinder has a feedline with 64 dual polarization feeds placed every ~30 cm which Nyquist sample the north-south sky over much of the frequency band. The signals from each dual-polarization feed are independently amplified, filtered to 400-800 MHz, and directly sampled at 800 MSps using 8 bits. The correlator is an FX design, where the Fourier transform channelization is performed in FPGAs, which are interfaced to a set of GPUs that compute the correlation matrix. The CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed to detect the BAO feature and constrain the distance-redshift relation. The lessons learned from its implementation will be used to inform and improve the final CHIME design.

Calibrating CHIME: a new radio interferometer to probe dark energy

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral hydrogen in the frequency range 400 { 800MHz over half of the sky, producing a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 { 2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that will yield constraints on the BAO power spectrum and provide a test-bed for our calibration scheme. I will discuss the CHIME calibration requirements and describe instrumentation we are developing to meet these requirements.

Silicon photomultiplier-based Compton Telescope for Safety and Security

A Compton gamma imager has been developed for use in consequence management operations and in security investigations. The imager uses solid inorganic scintillator, known for robust performance in field survey conditions. The design was constrained in overall size by the requirement that it be person transportable and operable from a variety of platforms. In order to introduce minimal dead material in the path of the incoming and scattered gamma rays, custom silicon photomultipliers (SiPMs), with a thin glass substrate, were used to collect the scintillation light from the scatter layers. To move them out of the path of the gamma rays, preamplification electronics for the silicon photomultipliers were located a distance from the imager. This imager, the Silicon photomultiplier Compton Telescope for Safety and Security (SCoTSS) is able to provide a one-degree image resolution in a ±45° field of view for a 10 mCi point source 40 m distant, within about one minute, for gamma-ray energies ranging from 344 keV to 1274 keV. Here, we present a comprehensive performance study of the SCoTSS imager.

A laser pulse stretcher made from optical fibres

Abstract We describe a simple device which splits a laser beam into many parts, sends it down optical fibres of different lengths and then recombines it. This has the effect of generating several short pulses which are temporally separated. We present an application in which the series of short pulses is used to simulate a single long pulse of the same total energy. This is useful in avoiding saturation effects caused by high instantaneous currents in photomultipliers.

A two-pixel Compton imager

We are designing a Compton imager for use in security investigations and in radiological incident remediation. Previously, results from simulations of a system consisting of several layers of pixellated solid scintillator for both the scatter and absorber detectors were reported. We have now established a two-pixel test stand for validation of the simulations. The stand consists of a single scatter pixel fixed in space, and a single absorber pixel affixed to a two-dimensional translator. Automated translation of the absorber pixel to different positions allows for the acquisition of data at multiple Compton scattering angles, thereby building up a dataset from an effectively multi-channel Compton imager. Here we present performance characteristics for an imager composed of a single 1 cm3 pixel of NaI(Tl) for the scatter detector, and a single 1 cm3 pixel of LaBr3 for the absorber detector.

Holographic beam mapping of the CHIME pathfinder array

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder radio telescope is currently surveying the northern hemisphere between 400 and 800 MHz. By mapping the large scale structure of neutral hydrogen through its redshifted 21 cm line emission between z∼0.8-2.5 CHIME will contribute to our understanding of Dark Energy. Bright astrophysical foregrounds must be separated from the neutral hydrogen signal, a task which requires precise characterization of the polarized telescope beams. Using the DRAO John A. Galt 26 m telescope, we have developed a holography instrument and technique for mapping the CHIME Pathfinder beams. We report the status of the instrument and initial results of this effort.

Recent results from VERITAS

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) [1] is a ground-based gamma-ray observatory used for a variety of observations at energies between 100 GeV and 30 TeV. This contribution reports on detections of two active galactic nuclei, W-Comae and 3C 66A, of the IBL class and discusses some features of their detection within the context of astroparticle physics, one of the central themes of the TAUP conference series.

Development of low cost liquid scintillator counters for cosmic ray experiments

Abstract Large area scintillation counters for use in an extensive air shower array have been developed. These detectors are based on liquid scintillator contained in vacuum-formed acrylic dishes and exhibit good spatial uniformity and timing resolution.

The optical delay line and pipeline: Concept and applications

Abstract We present a new method for reading out multichannel particle detectors based on optical fibre technology. By using different lengths of fibre to join detector elements to a phototube one can take advantage of the transit time of light in the fibre to allow several elements to be serviced by one phototube. We discuss two general classes of devices based on this technique.