Processing x-ray data on board the SMILE SXI

Abstract

SMILE (Solar Magnetosphere Ionosphere Link Explorer) is a collaborative mission between the European Space Agency and the Chinese Academy of Sciences that is scheduled to be launched in 2024 and will be placed in a highly elliptical, inclined, orbit. The on-board instrumentation will study interactions between the solar wind and the Earth's magnetosphere-ionosphere system by imaging the soft X-ray emission that results from solar wind charge exchange whilst simultaneously collecting information about the northern aurora with a UV imager and investigating the solar wind and magnetosheath plasma and magnetospheric field conditions using a Light Ion Analyzer and a magnetometer.The SXI (Soft X-ray Imager) is a wide field 'lobster-eye' telescope that is equipped with two 4510 x 4510 pixel CCDs with 18 µm pixel pitch. It will image X-rays (300 eV-2000 eV) through focusing optics that consist of an array of Micro Pore plates.The predicted X-ray event rate is expected to be low and the instrument will operate in photon counting mode so the SXI is designed to maximize the useful information returned to earth by identifying and storing individual events on board the spacecraft before transmitting the relevant information back to earth. This study investigates the baseline methods that will be implemented on-board to isolate and extract these events from the images amongst a more complicated particle background. The detector response is modelled and verified with calibration data from the CCD270.The work presented here by the Centre for Electronic Imaging at the Open University demonstrates the proposed method for isolating individual soft X-rays from images taken using the SMILE SXI and subsequently sorting these X-rays into data packets suitable for transmitting to earth. Different methods are tested with simulated and real data to optimize the proportion of useful events transmitted.

A model for photon counting X-ray event reconstruction uncertainty

“…It aimed to predict and analyse the effect of charge spreading on the additional uncertainty introduced into X-ray interaction event reconstruction in various X-ray detector architectures. This model uses a simplified version of the two threshold reconstruction technique commonly used for space based detectors [7,9]. In this process:…”

“…In addition, pattern matching is often used as a prelude to X-ray event grading, which is not always an option for low flux applications. The reconstruction and detection thresholds for a detector are often set in relation to the per-pixel expected noise, values three to five times the per-pixel rms noise are common (for example, [9,10]). This approach addresses the consequence of including too many noisy pixels during reconstruction but may ignore the effect of sub-threshold pixels containing charge.…”

Evaluation of sensors for the detection of energy resolved very soft x-ray fluorescence

“…The X-ray event threshold for a particular detector is often a multiple of the per pixel rms noise above the zero value (for example, 11 ). This is selected to ensure maximum detectability of X-rays whilst suppressing the number of noisy pixels falsely identified as X-rays.…”