Anthony F. Abbey

Readout modes and automated operation of the Swift X-ray Telescope

The Swift X-ray Telescope (XRT) is designed to make astrometric, spectroscopic, and photometric observations of X-ray emission from Gamma-ray Bursts and their afterglows in the energy band 0.2-10 keV. In order to provide rapid-response, automated observations of these randomly occurring objects without ground intervention, the XRT must be able to observe objects covering some seven orders of magnitude in flux, extracting the maximum possible science from each one. This requires a variety of readout modes designed to optimise the information collected in response to shifting scientific priorities as the flux from the burst diminishes. The XRT will support four major readout modes: imaging, two timing modes and photon-counting, with several sub-modes. We describe in detail the readout modes of the XRT. We describe the flux ranges over which each mode will operate, the automated mode switching that will occur and the methods used for collection of bias information for this instrument. We also discuss the data products produced from each mode.

The X-ray energy response of silicon Part A. Theory

Abstract In this, the first part of a two-part study of the interaction of soft X-rays with silicon, motivated by the calibration requirements of CCD imaging spectrometers in astronomy, we describe a Monte Carlo model of X-ray energy loss whose products are the energy- and temperature-dependences of (i) W , the average energy required to create an electron-hole pair, and (ii) the Fano factor F , W and F have invariably been treated as material constants in previous analyses of Si X-ray detector performance. We show that in fact, at constant detector temperature T , W is an increasing function of X-ray energy for E F is predicted to increase slowly with E . The temperature coefficient d W /d T has a calculated value ∼ 1 × 10 −4 K −1 at a typical CCD operating temperature of 170 K. We discuss the practical implications of these results. Finally, we describe our separate calculations of the near-edge variation of CCD quantum detection efficiency arising from silicon K-shell Extended X-ray Absorption Fine Structure (EXAFS).

SWIFT XRT Point Spread Function measured at the Panter end-to-end tests

The SWIFT X-ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X-ray emission from Gamma-ray bursts and their afterglows, in the energy band 0.2 - 10 keV. Here we report the results of the analysis of SWIFT XRT Point Spread Function (PSF) as measured during the end-to-end calibration campaign at the Panter X-Ray beam line facility. The analysis comprises the study of the PSF both on-axis and off-axis. We compare the laboratory results with the expectations from the ray-tracing software and from the mirror module tested as a single unit. We show that the measured HEW meets the mission scientific requirements. On the basis of the calibration data we build an analytical model which is able to reproduce the PSF as a function of the energy and the position within the detector.

Proton Damage Effects in EEV Charge Coupled Devices

An examination is conducted of the effects of low-energy protons on CCD performance to evaluate the potential effectiveness of space-borne observational instruments. Degradation is described as a function of incremental dose, irradiation temperature, or proton energy for several device architectures, some of which incorporate design features to minimize signal-charge/trapping-site interaction. Degradation of the charge transfer is studied for very low proton doses, and dark current is found to vary directly with proton dose. Displacement damage in the signal-transfer channels generates charge-trapping sites that have a negative effect on EEV CCD performance. Degradation of charge-transfer performance is shown to be the most significant hindrance to effective CCD operations for X-ray spectroscopic applications.

Direct measurement of sub-pixel structure of the EPIC MOS CCD on-board the XMM/NEWTON satellite

We have used a mesh experiment in order to measure the sub-pixel structure of the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40

In-orbit calibration activities of the XMM-Newton EPIC cameras

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First in-orbit measurements with the ROSAT XUV wide field camera

m-square pixels which have an open electrode structure in order to improve the detection efficiency for low-energy X-rays. We obtained restored pixel images for various X-ray event grades (e.g. split-pixel events, single pixel events, etc.) at various X-ray energies. We confirmed that the open electrode structure results in a distorted horizontal pixel boundary. The open electrode region generates both single pixel events and vertically split events, but no horizontally split events. Because the single pixel events usually show the best energy resolution, we discuss a method of increasing the fraction of single pixel events from the open electrode region. Furthermore, we have directly measured the thickness of the electrodes and dead-layers by comparing spectra from the open electrode region with those from the other regions: electrodes, electrode finger and channel stop. We can say that EPIC MOS CCDs are more radiation hard than front-illumination chips of ACIS on-board Chandra X-ray Observatory because of their extra absorption thickness above the charge transfer channel. We calcurated the mean pixel response and found that our estimation has a good agreement with that of the ground calibration of EPIC MOS CCD.Abstract We have used a mesh experiment in order to measure the sub-pixel structure of the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40 μm -square pixels which have an open electrode structure in order to improve the detection efficiency for low-energy X-rays. We obtained restored pixel images for various X-ray event grades (e.g. split-pixel events, single pixel events, etc.) at various X-ray energies. We confirmed that the open electrode structure results in a distorted horizontal pixel boundary. The open electrode region generates both single pixel events and vertically split events, but no horizontally split events. Because the single pixel events usually show the best energy resolution, we discuss a method of increasing the fraction of single pixel events from the open electrode region. Furthermore, we have directly measured the thickness of the electrodes and dead-layers by comparing spectra from the open electrode region with those from the other regions: electrodes, electrode finger and channel stop. We can say that EPIC MOS CCDs are more radiation hard than front-illumination chips of ACIS on-board Chandra X-ray Observatory because of their extra absorption thickness above the charge transfer channel. We calculated the mean pixel response and found that our estimation has a good agreement with that of the ground calibration of EPIC MOS CCD.

The spectroscopic performance of the Swift X-ray Telescope for gamma-ray burst afterglow studies

The combined effective area of the three EPIC cameras of the XMM-Newton Observatory, offers the greatest collecting power ever deployed in an X-ray imaging system. The resulting potential for high sensitivity, broad-band spectroscopic investigations demands an accurate calibration. This work summarizes the initial in-orbit calibration activities that address these requirements. We highlight the first steps towards effective area determination, which includes the maintenance of gain CTI calibration to allow accurate energy determination. We discuss observations concerning the timing and count-rate capabilities of the detectors. Finally we note some performance implications of the optical blocking filters.

Swift XRT effective area measured at the Panter end-to-end tests

The main design features and the early findings of the Rosat XUV wide field camera (WFC) are discussed. The most important data on the WFC telescope and detectors are presented. The WFC operational features, observing efficiency, filter performance, thermal performance star tracker performance, and single-event upsets are discussed. The first WFC images are compared with preflight calibration data.

Algorithm for locating PSF-like events and computing the centroid in x-ray images

The Swift X-ray Telescope is a powerful instrument for measuring the X-ray spectral properties of GRB afterglows. The spectroscopic capabilities are obtained through the energy resolving properties of the X-ray CCD imager in the focal plane of the X-ray Telescope. A range of CCD operating modes allow GRB afterglows to be followed over 5 orders of brightness as the afterglow decays. The spectroscopic response in each mode has been determined as part of the XRT calibration program and is being incorporated into the XRT instrument response matrices. These responses are being used to simulate GRB spectra as part of the pre-launch mission planning for Swift.