Observations of binary and millisecond pulsars with a baseband recording system

We have built a new fast data acquisition system for pulsars, designed to implement the technique of coherent dispersion removal in software. The Mark IV system digitizes the complex signal voltages in two orthogonal polarizations before detection, Nyquist-sampling either a 10 MHz bandwidth with 2-bit quantization or a 5 MHz bandwidth with 4-bit quantization. The data stream is stored on a combination of magnetic disks and tapes for off-line processing. Data analysis is performed using a special-purpose parallel processor. The effects of interstellar dispersion are removed by convolving the data time-series with the inverse of the interstellar medium "chirp function." Cross-products are formed from the dedispersed signals, and then are folded modulo the predicted pulse period. In this fashion we obtain the full set of Stokes parameters for every observation.; We have used the Mark IV system extensively at the Nuffield Radio Astronomy Laboratories at Jodrell Bank, England. We present high-time-resolution polarimetric profiles for several millisecond pulsars, based on data obtained there.; Double-neutron-star binary pulsars are of particular interest because they offer an opportunity to probe the strong-field regime of gravitational theories. Using the Jodrell Bank telescope we observed PSR B1534+12 for several hours a day for a span of approximately one month. Appending this high-quality data set to existing timing observations from Arecibo and Green Bank Observatories has led to a much-improved value of the orbital period derivative. This measurement provides only the second confirmation of the general-relativistic prediction of quadrupolar gravitational radiation. Alternatively, under the assumption that general relativity is correct, the distance to the pulsar may be determined; we derive a value of 1.1 {dollar}pm{dollar} 0.2 kpc, somewhat higher than the dispersion-measure distance of 0.7 {dollar}pm{dollar} 0.2 kpc. We also report improved mass measurements for this system: we find the masses of the pulsar and its neutron-star companion each to be 1.339 {dollar}pm{dollar} 0.003{dollar}Msb{lcub}odot{rcub}.{dollar}; Lastly, we present preliminary timing measurements from the Mark IV instrument at the newly-upgraded Arecibo Observatory, and discuss implications for future observations.