Showing papers by "Jordi Portell published in 2012"

LOFT - The large observatory for x-ray timing

Abstract: The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated ( 2 peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of

The on-board data handling concept for the LOFT Large Area Detector

Abstract: The Large Observatory for X-ray Timing (LOFT) is one of the four candidate ESA M3 missions considered for launch in the time-frame of 2022. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black holes and neutron stars. The LOFT scientific payload consists of a Large Area Detector and a Wide Field Monitor. The LAD is a 10 m^2-class pointed instrument with high spectral (200 eV @ 6 keV) and timing (< 10 {\mu}s) resolution over the 2-80 keV range. It is designed to observe persistent and transient X-ray sources with a very large dynamic range from a few mCrab up to an intensity of 15 Crab. An unprecedented large throughput (~280.000 cts/s from the Crab) is achieved with a segmented detector, making pile-up and dead-time, often worrying or limiting focused experiments, secondary issues. We present the on-board data handling concept that follows the highly segmented and hierarchical structure of the instrument from the front-end electronics to the on-board software. The system features customizable observation modes ranging from event-by-event data for sources below 0.5 Crab to individually adjustable time resolved spectra for the brighter sources. On-board lossless data compression will be applied before transmitting the data to ground.

Data Management at Gaia Data Processing Centers

Abstract: Gaia is a European Space Agency mission that will deal with large volumes of data that have to be processed at, and transferred between, different data processing centers (DPCs) in Europe. Managing the data and the associated databases will be a significant challenge. This paper presents the different data management configurations that have been evaluated at the Gaia DPCs in order to cope with the requirements of Gaia’s complex data handling.

Outlier-Resilient Entropy Coding

Abstract: Many data compression systems rely on a final stage based on an entropy coder, generating short codes for the most probable symbols. Images, multispectroscopy or hyperspectroscopy are just some examples, but the space mission concept covers many other fields. In some cases, especially when the on-board processing power available is very limited, a generic data compression system with a very simple pre-processing stage could suffice. The Consultative Committee for Space Data Systems made a recommendation on lossless data compression in the early 1990s, which has been successfully used in several missions so far owing to its low computational cost and acceptable compression ratios. Nevertheless, its simple entropy coder cannot perform optimally when large amounts of outliers appear in the data, which can be caused by noise, prompt particle events, or artifacts in the data or in the pre-processing stage. Here we discuss the effect of outliers on the compression ratio and we present efficient solutions to this problem. These solutions are not only alternatives to the CCSDS recommendation, but can also be used as the entropy coding stage of more complex systems such as image or spectroscopy compression.

The on-board data handling concept for the LOFT large area detector

Abstract: The Large Observatory for X-ray Timing (LOFT) is one of the four candidate ESA M3 missions considered for launch in the timeframe of 2022. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black holes and neutron stars. The LOFT scientific payload consists of a Large Area Detector and a Wide Field Monitor. The LAD is a 10m2-class pointed instrument with high spectral (200 eV @ 6 keV) and timing (< 10 μs) resolution over the 2-80 keV range. It is designed to observe persistent and transient X-ray sources with a very large dynamic range from a few mCrab up to an intensity of 15 Crab. An unprecedented large throughput (~280.000 cts/s from the Crab) is achieved with a segmented detector, making pile-up and dead-time, often worrying or limiting focused experiments, secondary issues. We present the on-board data handling concept that follows the highly segmented and hierarchical structure of the instrument from the front-end electronics to the on-board software. The system features customizable observation modes ranging from event-by-event data for sources below 0.5 Crab to individually adjustable time resolved spectra for the brighter sources. On-board lossless data compression will be applied before transmitting the data to ground.