LOFT - the Large Observatory for X-ray Timing

TL;DR

LOFT was a proposed ESA X-ray observatory designed for fast timing studies of black holes and neutron stars, featuring a large-area detector with revolutionary capabilities, though it was not selected for launch.

Contribution

This paper details the design and technological advancements of LOFT's Large Area Detector, highlighting its innovative lightweight, large-area X-ray detection capabilities.

Findings

Design of a 10 m^2-class X-ray detector with low mass per unit area

Use of silicon drift detectors and capillary-plate collimators for large-area X-ray detection

LOFT's robust design ready for future ESA proposals

Abstract

LOFT (the Large Observatory for X-ray Timing), is a mission concept that was considered by ESA as a candidate for an M3 mission and has been studied during an extended >2-years long assessment phase. The mission was 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 m^2-class pointed instrument with about 15 times the collecting area of the largest past timing missions (as the Rossi XTE) over the 2-30 keV range (30-80 keV expanded), combined with CCD-class spectral resolution, which holds the capability to revolutionise studies of X-ray variability down to the millisecond time scales. Its ground-breaking characteristic is a mass per unit surface in the range of 10 kg/m^2, enabling an effective area of about 10 m^2 (at 8 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 drift detectors and capillary-plate X-ray collimators. Although the LOFT mission has not been down-selected for launch in the M3 ESA programme (with launch in 2022-2024), during the assessment phase most of the trade off have been closed leading to a robust and well documented design which will be re-proposed in the future ESA calls. In this paper, we will summarize the characteristics of the LAD instrument and briefly describe the status of the detectors design.