Determination of the Position of GX2 + 5 with Copernicus

Abstract

GX2 + 5 (2U1728–24) has been observed on two occasions, using the University College X-ray experiment on board Copernicus. Three of the X-ray detectors were used for the observations, the collimated proportional counter, sensitive in the range 1–3 Å and the two grazing incidence telescopes which are sensitive in the ranges 3–9 Å and 6-18 Å respectively. The field of view of the 1–3 Å detector is about 3 arc deg (FWHM); the two low energy detectors have three possible fields of view, 10, 2 and 1 arc min (FWHM) for the 3–9 Å 10, 6 and 2 arc min (FWHM) for the 6–18 Å detector. By scanning the approximate location of a source, its position can be determined from the count rates of the 3–9 Å and 6–18 Å detectors, while any variation in source intensity is monitored on the wide angle 1–3 Å counter. A complete description the experiment, the measurement of the alignment of the X-ray reflecting mirror axes with respect to the Princeton Ultraviolet Experiment Fine Error Sensor (FES) and the instrument calibration will be given elsewhere.