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The future ground based gamma-ray observatory, the Cherenkov Telescope Array (CTA), will soon enter its construction phase. This work therefore looks into providing a better model of one of the small size telescopes, the Gamma Cherenkov Telescope (GCT), for input into Monte Carlo simulations. Evaluation of these models shows that both a telescope equipped with MaPM (GCTM) and SiPM (GCTS) detector modules should meet if not exceed certain CTA requirements. To determine possible early science deliverables, a study into the performance of a small 7 telescope array, along with an extrapolation up to the full complement of SSTs is presented. This reveals promising results for both configurations, with GCTS performing better than GCTM. This work also presents an investigation into the use of local muons as a form of absolute calibration of the GCT telescope. It has been shown that, while there are some difficulties, the method should be possible. The remainder of this thesis presents results obtained from applying the clustering algorithm DBSCAN to the Fermi-LAT data in the very high energy (VHE) regime. This includes 9 sources detected in the Pass 7 reprocessed data set and 70 in the improved Pass 8 data set. These sources represent promising candidates for follow-up observations with current ground-based gamma-ray observatories and helps to frame the science goals of CTA.

This thesis is concerned with the development of, position-sensitive, Transition Edge Sensors (TES) operating at cryogenic temperatures (~ 0.1 K). The Distributed Read-Out Imaging Device (DROID) concept uses TES read-out at both ends of a linear X-ray absorber, to derive, through heat diffusion, both spectral and spatial information. Potentially, DROIDs offer a simpler technological alternative to the development of large area pixel arrays for future X-ray space observatories (Chapter 1). Chapter 2 presents a comprehensive review of the theory of microcalorimeter detectors. A finite-element model is established in Chapter 3, to numerically simulate the response of the DROID to an X-ray photon, as well as the noise spectral density at the detector outputs, including frequency dependent correlations between the two TESs. In Chapter 4 this model is used to implement pre-existing algorithms, based on the use of the optimal filter, to calculate the position and energy resolution along the length of experimental DROID designs. We show that these algorithms do not lead to optimum performance under all conditions and then derive the true optimal filters, based on least-squares minimisation of the total noise power in the DROID. By numerical simulation we show that significant improvements in both the energy and in particular, the position resolution, are theoretically possible. The design and experimental characterisation of two prototype DROIDs are described in Chapter 6 and 7, using the equipment described in Chapter 5. The first X-ray results from a prototype TES DROID, using single TES read-out, are reported. These results demonstrate proof of concept, confirming spatial sensitivity along the DROID, through the actual spectral and spatial resolutions are limited by the availability of only a single read-out channel.

In this thesis we study Saturn’s ultraviolet dayside auroras mainly using images from the Hubble Space Telescope. We investigate a variety of different types of auroral emission observed in the database of images compiled between 1997 and 2013. In equinoctial data from 2009 two different types of features are investigated. In the dawn sector patches of emission are observed that are found to lack direct conjugacy between the two hemispheres and instead are displaced in local time. A production mechanism related to ULF waves is suggested, plausibly driven by drift-bounce resonance. Dusk transient auroral emission is also observed and found to be strictly non-conjugate. A suggested explanation is that the transient patches are related to newly-opened flux tubes where the hemispheric symmetry is broken via the interplanetary magnetic field Y component. A further study uses data from the Cassini spacecraft during passages through the solar wind in conjunction with Hubble Space Telescope images from 2011 and 2012 in order to investigate how changes in the Interplanetary Magnetic Field strength affect the auroral emission at Saturn. It is found that during intervals of positive interplanetary magnetic field the auroral emission in the dusk sector is enhanced as opposed to cases of negative field strength where there is little emission observed in the dusk sector. This supports earlier interpretations that this emission is due to low latitude dayside reconnection and open flux production. The final study in this thesis uses the entire dataset of Hubble Space Telescope images to investigate auroral storm events. There are 12 such events found in the database with statistics showing that storms are present ~12% of the time. We deduce from the statistics and observations that storms are likely to last ~16 hours or ~1.5 Saturn rotations.

Mars Sample Return is the next major step in the search for life beyond Earth. Mineralogical studies have revealed a wetter, more dynamic Mars than previously considered; the past environments of Mars could have hosted life and the search for its remains is a major scientific preoccupation. The return to Earth of the very best samples requires an effective prioritization and selection process, thus there is a requirement for a triage instrument which examines mineral phases in situ to determine the habitability potential of a region and to detect important biosignatures contained in any rock. This thesis demonstrates the viability of a pyrolysis-Fourier transform infrared spectroscopy (FTIR) instrument to fulfil these mission requirements. Thermal decomposition techniques have long been used on Mars to analyse solid samples, and FTIR instruments have been successfully deployed on the Martian surface. The combination of the two presents a resource efficient and robust analytical solution. Investigations were conducted using pyrolysis-FTIR to show how habitability and the biosignature preservation potential of rocks can be assessed through the release of key gases, namely carbon dioxide, water and sulfur dioxide. The sensitivity limits for detecting organic matter and the effects of different mineral matrices on the organic compound signal were also investigated though measurement of methane and larger hydrocarbon compounds. Finally a field study was conducted using samples collected from a sulfate stream ecosystem which represents an analogue for the Hesperian of Mars. The investigations have shown that pyrolysis-FTIR, through utilisation of different temperature modes and the qualitative and quantitative feedback of resulting spectra, provides adequate information to determine mineral phases relating to habitability. Pyrolysis-FTIR detects organic compounds present in quantities as low as tens of parts-per-million. Sulphates and chlorinated mineral phases diminish organic compound signals, but combustion products offer another avenue for detection. The field study demonstrated that a phased pyrolysis-FTIR protocol will select the most valuable samples. This thesis includes recommendations for the progress of pyrolysis-FTIR to the next design iteration.

New results of X-ray polarisation detection efficiencies are presented for two small pixel devices. EEV Ltd. have designed the first CCD X-ray polarimeter with an improved deep depletion layer of 80 urn, to maximise the device quantum efficiency at energies above 1 keV. A novel design concept has been utilised to minimise the pixel dimension whilst maximising production, the CCD has 4x9 um2 pixels. This device was tested and has been shown to be greater than a factor of two more efficient for polarisation measurements above 10 keV, than previously tested CCDs. The first successful measurements below 10 keV show a 5 - 10 % polarisation detection efficiency (modulation factor, M(E)), a significant result, due to X-ray optics having greater effective area below 10 keV. The smallest pixel CCD to date, with 2.4 um2 pixels, designed for optical purposes by Philips Ltd., is shown to have 26.2 % modulation at 10 keV. From the analysis of the data from these devices it has been recognised that charge diffusion, and thus the depletion depth, has a significant effect on the polarisation measurements. A model has been written to simulate polarised X-ray interactions in CCDs, and is shown to successfully model thinly depleted devices (Kodak KAF1400), in terms of polarisation detection efficiency. Further improvements have been identified to provide an accurate model for deeply depleted devices, in order to create a tool for optimising future CCD polarimeters. The modulation factors, M(E), for a 0.5 um2 pixel CCD have been estimated using the model, and it has been shown that a device of this type would provide a further factor of 2 improvement in M(E), with a significant measurement as low as 5 keV. The feasibility of a future mission including a CCD X-ray polarimeter has been investigated in detail, in terms of current and future technology. The XMM and the XEUS optics are considered in conjunction with both the EEV polarimeter and the modelled 0.5 urn2 pixel CCD. Two types of Astronomical sources are taken into account over a 5 - 20 keV energy range: bright galactic objects, e.g. The Crab Nebula faint extragalactic objects e.g. Active Galactic Nuclei (AGN). Using the XEUS optics, a 25 m focal length and an effective area maximised to 1 m2 at 1 keV yields observation times of less than 105 sees for a Crab measurement (polarisation 10 - 20 %, below 12.5 keV) and of the order 104 sees or less using a 0.5 urn2 pixel CCD. For measurements of the more faint AGN (polarisation 10 - 20 %) observation times are of the order 106 sees or below for the EEV CCD (7.5 - 10 keV) and the 0.5 um2 device (5 - 12.5 keV). Employing the XEUS optics for the measurement of the polarisation of AGN requires no further technological advancement if the EEV polarimeter is utilised, and the production of a 0.5 um2 pixel CCD is said to be within easy reach according to manufacturers.

Charge Coupled Devices (CCDs) are low power, robust detectors promising medium spectral resolution, high spatial resolution and a high signal to noise ratio. It is for this reason that CCDs have become the preferred focal plane detector in all x-ray astronomy missions due for launch in the 1990s and early in the next millennium. The absorption of x-rays by a CCD is modulated by the transmission of the complex electrode structures and passivation layers on its front surface. Since the path length of soft x-rays (0.l1 - 2 keV) is of the same order as the thickness of these layers, fine structure in the quantum efficiency (Q(E)) around absorption edges can have a profound influence on the response of the CCD. This thesis presents the work done in investigating fine structure effects in the Q(E) of x-ray CCDs and the impact that these effects will have on astronomy missions. The state of x-ray astronomy as we move into the CCD-mission era is reviewed in Chapter 2. the operation of a CCD as an x-ray detector is then described. The extensive set of experiments carried out at the Daresbury Synchrontron Radiation Source (SRS) to map the Q(E) of JET-X CCDs are detailed, including a description of the first use of the new, low beam current mode of SRS operation. Chapter 5 describes the origins and expression of X-ray Absorption Fine Structure (XAFS) in the CCD response. The instruments that make up the JET-X Focal Plane Cameras are then reviewed. In Chapter 7 the importance of calibrating JET-X accurately is shown by analysing the impact of XAFS in the detector sub-systems. It is shown that XAFS threaten the scientific return from current and future x-ray astronomy missions. In Chapter 8 the information contained by the fine structure in the CCD Q(E) is extracted and analysed to obtain the thickness and structure of the inert layers on the surface of the CCD, and also to improve models of the CCD response. Finally the work is summarised and additional further work is suggested.

This thesis describes the calibration of CsI- and KBr-coated microchannel plate (MCP) detectors using the Daresbury Synchrotron Radiation Source (SRS). This work was carried out as part of the calibration programme for the Advanced X-ray Astrophysics Facility (AXAF). The AXAF High Resolution Camera (HRC) consists of two MCP detectors: HRC-I, optimised as an imaging detector, and HRC-S, optimised as the read-out detector for a dispersive spectrometer. Accurate knowledge of the MCP quantum efficiency (QE) variation with energy is particularly important for HRC-S so that atomic absorption edge-related features in the MCP glass and photocathode are not misinterpreted as emission features in astrophysical spectra. The MCPs were calibrated on three beamlines at the SRS, which covered the energy ranges 50-350eV, 250-1400eV and 2-6keV. Calibration included measurement of QE as X-ray energy and incidence angle were varied. The ratio of the QE of CsI- and KBr-coated MCPs was also determined and gain decay of the MCPs was measured as charge was abstracted from a small area. Several significant features in QE were noted, a number of which exhibited characteristics such as white lines, slow onset and energy shifts. There were however, problems with measurement of the monochromator responses at the SRS, which cast doubt upon the accuracy of the QE-energy curves produced. The variation of QE with energy and angle measured at Daresbury was modelled. An existing model was updated to take account of the channel bias angle and was able to reproduce the general features of the QE-energy curves. An attempt was then made to model linear absorption coefficient and hence reproduce the white lines visible on some of the edge-related QE features. The final part of the thesis considers and models the effect of thermal annealing upon the QE of CsI-coated MCPs.

This thesis is concerned with the development of CdZnTe compound semiconductor detectors for hard X-ray astronomy. The advent of multilayer coated focusing optics for hard X-rays creates the need for compact solid-state X-ray detectors with substantial quantum efficiency above 10 keV. CZT is a material with the necessary properties to meet the requirements. Excellent results from commercially obtained CdZnTe detectors are presented in Chapter 4 of this work. Low-noise preamplifiers and Peltier coolers were employed to obtain high-resolution X-ray and gamma-ray spectra over the 2 - 60 keV energy range. 55Fe spectra have been acquired with a resolution of < 218eV FWHM and peak-to-background ratios in excess of 200:1. Data have been obtained at a range of energies to enable measurements of fundamental properties of the detector and material, including the Fano factor. A program of modelling was also undertaken and the work is presented in Chapter 3. Using the simulation, the mobility-lifetime products of the CZT material were determined to be ee = (3.9 0.15) x 10-3 cm2V-1 and hh = (1.2 0.2)x 10-5 cm2V-1. A dead-layer is hypothesized to lie beneath the electrodes of the CZT devices and the model was used to parameterize the depth of this region to 500-1000nm. Two-dimensional FITS arrays were also generated to describe the detector response to a range of input energies. Chapter 5 describes the manufacture and processing of CZT crystals. Spectroscopic crystals were successfully produced, including a novel device geometry. Finally, work intended to form the basis for pixel array development is presented in Chapter 6.

There are opportunities in space science for UV imaging instruments with photon counting sensitivity that can accommodate scenes with large dynamic range whilst maintaining the ability for very high spatial resolution imaging when desired. Current UV imaging space instruments have limitations that reduce the performance in meeting this challenge. The microchannel plate detector has an established heritage in UV astronomy and provides low noise single photon counting imaging with high spatial resolution, high dynamic range, solar-blind capability and radiation hardness. To fully complement this performance requires a new detector readout system with great flexibility in processing individual photon events, achieving high spatial resolution and with high count rate capability. An image readout system has been developed that utilises a new, low-noise capacitive division readout and has the potential to meet these high performance requirements. Unlike traditional centroiding image readout schemes that use a fixed pulse shaping time, this system has the capability to adapt to the luminosity conditions and the flexibility to optimise the image spatial resolution against the photon event rate. The design employs a low-noise front-end electronics system that uses a pulse digitisation approach to transfer the signal filtering capability into the digital signal processing domain, enabling the flexibility to select the optimum shaping scheme for the required resolution and count rate. The development progress of the instrument and imaging software is described for both a fixed shaping time readout design and an adaptable shaping solution and new performance results for the capacitive division readout are presented.