P. J. Smith

Organotin chemistry : XII. The structure and reactions of some mono-organotin(IV) compounds

Abstract The preparation, 119m Sn Mossbauer spectra, and 119 Sn NMRspectra, of a series of mono-organotin(IV) compounds, RSnX 3 (X = S, Cl, or O), are reported. The organostannatranes, RSn(OCH 2 CH 2 ) 3 N, constitute a new family of readily accessible organotin trialkoxides.

Organotin chemistry : IX. Investigations of the structure of some 1,3-difunctional tetraalkyl distannoxanes by mössbauer spectroscopy and 119Sn Heteronuclear double magnetic resonance☆

Abstract The 119mSn Mossbauer and 119Sn NMR spectra of a series of functionally disubstituted symmetrical organostannoxanes, XBu2SnOSnBu2X, containing a range of substituents X, have been recorded. The results are compatible with a dimeric, ladder-type of structure for these compounds, in which the two tin atoms are both pentacoordinate and occupying very similar trigonal bipyramidal environments.

Crystal structure and Mössbauer spectrum of dimethyltin dichloride

The crystal structure of dimethyltin dichloride has been solved and the parameters have been refined by three-dimensional least-squares analysis. The environment of the tin atoms is considerably distorted from the regular tetrahedral co-ordination towards octahedral, because of the association between neighbouring molecules.The Mossbauer spectra of the dialkyltin dichlorides are discussed in terms of this structure, and of the dialkyltin difluorides in terms of a trans-octahedral configuration.

Organotin chemistry : VI. The preparation and Mössbauer spectra of some butyltin(IV), dialkyltin(IV) and simple and mixed hexahalogenostannate complexes☆

Abstract The Mossbauer spectra of some complexes of butyltin trichloride, dimethyltin dichloride and dioctyltin dichloride have been recorded, and the observed quadrupole splittings compared with the relative values predicted for the point-charge models. In the simple and mixed tetraethylammonium hexahalogenostannate ions, (Et 4 N + ) 2 SnX 2− 6 and (Et 4 N + ) 2 SnX 4 Y 2− 2 , there is a linear relationship between the isomer shift and the sum of the (Mullikan) electronegativities of the ligands.

A Large Area Detector proposed for the Large Observatory for X-ray Timing (LOFT)

The Large Observatory for X-ray Timing (LOFT) is one of the four candidate ESA M3 missions considered for launch in the 2022 timeframe. 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 is composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a 10 m2-class pointed instrument with 20 times the collecting area of the best past timing missions (such as RXTE) over the 2-30 keV range, which holds the capability to revolutionize studies of X-ray variability down to the millisecond time scales. Its ground-breaking characteristic is a low mass per unit surface, enabling an effective area of ~10 m2 (@10 keV) at a reasonable weight. The development of such large but light experiment, with low mass and power per unit area, is now made possible by the recent advancements in the field of large-area silicon detectors - able to time tag an X-ray photon with an accuracy <10 μs and an energy resolution of ~260 eV at 6 keV - and capillary-plate X-ray collimators. In this paper, we will summarize the characteristics of the LAD instrument and give an overview of its capabilities.

The large area detector of LOFT: the Large Observatory for X-ray Timing

LOFT (Large Observatory for X-ray Timing) is one of the five candidates that were considered by ESA as an M3 mission (with launch in 2022-2024) and has been studied during an extensive assessment phase. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black holes and neutron stars. Its pointed instrument is the Large Area Detector (LAD), a 10 m2-class instrument operating in the 2-30keV range, which holds the capability to revolutionise studies of variability from X-ray sources on the millisecond time scales. The LAD instrument has now completed the assessment phase but was not down-selected for launch. However, during the assessment, most of the trade-offs have been closed leading to a robust and well documented design that will be reproposed in future ESA calls. In this talk, we will summarize the characteristics of the LAD design and give an overview of the expectations for the instrument capabilities.

The LOFT ground segment

LOFT, the Large Observatory For X-ray Timing, was one of the ESA M3 mission candidates that completed their assessment phase at the end of 2013. LOFT is equipped with two instruments, the Large Area Detector (LAD) and the Wide Field Monitor (WFM). The LAD performs pointed observations of several targets per orbit (~90 minutes), providing roughly ~80 GB of proprietary data per day (the proprietary period will be 12 months). The WFM continuously monitors about 1/3 of the sky at a time and provides data for about ~100 sources a day, resulting in a total of ~20 GB of additional telemetry. The LOFT Burst alert System additionally identifies on-board bright impulsive events (e.g., Gamma-ray Bursts, GRBs) and broadcasts the corresponding position and trigger time to the ground using a dedicated system of ~15 VHF receivers. All WFM data are planned to be made public immediately. In this contribution we summarize the planned organization of the LOFT ground segment (GS), as established in the mission Yellow Book1. We describe the expected GS contributions from ESA and the LOFT consortium. A review is provided of the planned LOFT data products and the details of the data flow, archiving and distribution. Despite LOFT was not selected for launch within the M3 call, its long assessment phase ( >2 years) led to a very solid mission design and an efficient planning of its ground operations.

The digital data processing concepts of the LOFT mission

The Large Observatory for X-ray Timing (LOFT) is one of the five mission candidates that were considered by ESA for an M3 mission (with a launch opportunity in 2022 - 2024). LOFT features two instruments: the Large Area Detector (LAD) and the Wide Field Monitor (WFM). The LAD is a 10 m2-class instrument with approximately 15 times the collecting area of the largest timing mission so far (RXTE) for the first time combined with CCD-class spectral resolution. The WFM will continuously monitor the sky and recognise changes in source states, detect transient and bursting phenomena and will allow the mission to respond to this. Observing the brightest X-ray sources with the effective area of the LAD leads to enormous data rates that need to be processed on several levels, filtered and compressed in real-time already on board. The WFM data processing on the other hand puts rather low constraints on the data rate but requires algorithms to find the photon interaction location on the detector and then to deconvolve the detector image in order to obtain the sky coordinates of observed transient sources. In the following, we want to give an overview of the data handling concepts that were developed during the study phase.

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

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.

Optimisation of the design for the LOFT large area detector module

LOFT (Large Observatory for X-ray Timing) is an X-ray timing observatory that, with four other candidates, was considered by ESA as an M3 mission (with launch in 2022-2024) and has been studied during an extensive assessment phase. Its pointed instrument is the Large Area Detector (LAD), a 10 m 2 -class instrument operating in the 2-30 keV range, which is designed to perform X-ray timing of compact objects with unprecedented resolution down to millisecond time scales. Although LOFT was not downselected for launch, during the assessment most of the trade-offs have been closed, leading to a robust and well documented design that will be reproposed in future ESA calls. The building block of the LAD instrument is the Module, and in this paper we summarize the rationale for the module concept, the characteristics of the module and the trade-offs/optimisations which have led to the current design.