Semiphysical Simulation Technique of X-Ray Pulsar Signals Detected at the Spacecraft

Abstract

The existing semiphysical simulation systems for X-ray pulsar signals are predicated on assuming the period of arrived signal is constant within a given time-span, thus cannot accurately simulate photon arrivals as seen by a detector on a moving spacecraft. In this paper, an alternative semiphysical simulation technique is proposed. The real-time photon arrival rate at the spacecraft is computed considering the Doppler effects and various large-scale time-space effects; then, it is transmitted to the digital-to-analog converter (DAC) using a high-speed interconnect. The output voltage signal of DAC, which is proportional to the arrival rate function, is used to modulate the visible light source to generate an optical signal that is ultimately converted to a photon-event time stamp after attenuation, detection, and time labeling. The digital-to-analog conversion avoids truncation errors that arise with the traditional methods using frequency synthesis. The main experiment results are that the observed profiles of the simulated data have almost the same shape and variation with observation time as those of real data; for observation times longer than 140 s, the correlation coefficients between the simulated profiles and the standard one reach above 0.99 with time-transformation, which indicates the validity and high performance of the proposed simulation technique.