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LOFT Large Area Detector An Analysis of the usage/popularity of the many PCA/EDS/EA data modes on RXTE

posted on 2023-05-25, 20:29 authored by Alan Giles
The NASA Rossi X-ray Timing Explorer (RXTE) (Bradt et al., 1990) mission which flew from late 1995 to early 2012 became one of NASA’s longest running astrophysics missions. RXTE contained 3 complimentary experiments - the Proportional Counter Array (PCA) provided by the Goddard Space Flight Center (GSFC), the High Energy X-ray Timing Experiment (HEXTE) provided by The University of California at San Diego (UCSD) and the All Sky Monitor (ASM) provided by the Massachusetts Institute of Technology (MIT). The large area, high time resolution, PCA provides the ‘bench-mark’ for many aspects of the Large Area Detector (LAD) experiment proposed on the ESA LOFT mission. The PCA comprised 5 notionally identical Proportional Counter Unit (PCU) detectors. These detectors were comprehensively described, particularly the calibration aspects, in Jahoda et al. (2006) (and references therein). Only a few of these details are directly relevant to the study reported here. The scientific data from the PCA (ignoring housekeeping, health & safety and commanding) was all produced by a single additional box known as the Experiment Data System (EDS). This box was also provided by MIT and although operated and monitored as a separate device by the MIT team was, for scientific purposes, effectively part of the PCA and was routinely operated by the staff of the Science Operation Facility (SOF) at GSFC. The Guest Observer Facility (GOF), also at GSFC, ran the proposal rounds and generated the final package of FITS format data files delivered to a successful Principal Investigator (PI) once their observations had been executed. The PI then had one year’s priority on the data before it became public. The EDS had many operating modes which a PI could select to optimise the use of the data from the PCA and ensure that they got the required information back to the ground, particularly for the brighter X-ray sources. The types of operating modes available and the frequency or ‘popularity’ of their use form the subject of this report. This information may serve as a guide to the suitable data modes for inclusion with the LAD experiment on LOFT since this will essentially be observing the same set of target sources. Such follow-on observations by the LAD will have a ~16x increase in area (compared to the whole PCA) with corresponding increase in detected count rate and telemetry loading, much better energy resolution and more PHA channels.


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