X-ray astronomy observations with a xenon filled fluorescence gated detector

The University of Tasmania xenon filled multiwire proportional counter provides post-flight analysis of data in both normal and fluorescence gated modes. Fluorescence gating leads to improved energy resolution above the K-edge in xenon (35-keV). Theoretical and laboratory studies suggest that sensitivity for detection of weak sources may also be improved in background-limited situations. This has not previously been demonstrated in astronomical observations. We observed the X-ray pulsar GX 1+4 during a balloon flight from Alice Springs, Australia and analysed the data in both modes. Preliminary results suggest that the sensitivity was little changed by the use of fluorescence gating, but that energy resolution was improved. An anomaly exists in the background at ∼60-keV. Mathematical analysis and Monte Carlo simulation show that fluorescence gating cannot be used in a small energy range about 60-keV.