Millisecond pulsar observation system using AOS

Extract

Communications Research Laboratory (CRL) developed a new millisecond pulsar observation system which used an Acousto-Optic Spectrometer (A0S). An AOS is simple and effective at dividing a wide band signal into many channels simultaneously. Using this system, we started preliminary observations of PSR1937+21 for the purpose of precise measurements of millisecond pulsar’s pulse timing.

Fig. 1 shows a block diagram of our observation system using the 34m antenna of CRL. This antenna has several receivers (1.5, 2, 5, 8, 10, 15, 22, 43 GHz) with selective polarizer. We use 1.5GHz or 2GHz band for pulsar observations. An IF signal with 50MHz bandwidth is divided to 200kHz × 256ch by the AOS. The speed of data transporting rate from the camera is about 13μs which limits a time resolution. We get 100 bins per one period for PSR1937+21. The video averaging processor works as two 8bits A/D converters and an averager which allows 2²⁴ pulses’ addition in each channel. The averaged data of each channel are combined after de-dispersion processing which is carried out in 1/1000 steps of the pulsar period. ¿From this final profile, the peak phase is defined as arrival pulse timing. Host#2 calculates the a priori pulse period by TEMPO program, and supplies it in real time to the synthesizer which controls the averaging trigger clock of the timing signal generator. The reference clock of this system is synchronized with UTC (CRL) via the GPS satellites. The difference between the reference clock and the internal clock of the timing signal generator is monitored using a time interval counter.