Radio pulse properties of the millisecond pulsar PSR J0437-4715. I. Observations at 20 centimeters

We present a total of 48 minutes of observations of the nearby, bright millisecond pulsar PSR J0437-4715 taken at the Parkes Observatory in Australia. The data were obtained at a central radio frequency of 1380 MHz using a high-speed tape recorder that permitted coherent Nyquist sampling of 50 MHz of bandwidth in each of two polarizations. Using the high time resolution available from this voltage recording technique, we have studied a variety of single-pulse properties, many for the first time in a millisecond pulsar. We show that individual pulses are broad band, have pulse widths ranging from similar to 10 (similar to 0.degrees 6 in pulse longitude) to similar to 300 mu s (similar to 20 degrees) with a mean pulse width of similar to 65 mu s (similar to 4 degrees), exhibit a wide variety of morphologies, and can be highly linearly polarized. Single pulse peaks can be as high as 205 Jy (over similar to 40 times the average pulse peak), and have a probability distribution similar to those of slow-rotating pulsars. We observed no single pulse energy exceeding similar to 4.4 times the average pulse energy, ruling out "giant pulses" as have been seen for the Crab and PSR B1937+21 pulsars. PSR J0437-4715 does not exhibit classical microstructure or show any signs of a preferred timescale that could be associated with primary emitters; single pulse modulation has been observed to be consistent with amplitude-modulated noise down to timescales of 80 ns. We observe a significant inverse correlation between pulse peak and width. Thus, the average pulse profile produced by selecting for large pulse peaks is narrower than the standard average profile. We find no evidence for "diffractive" quantization effects in the individual pulse arrival times or amplitudes as have been reported for this pulsar at lower radio frequency using coarser time resolution, Overall, we find that the single-pulse properties of PSR J0437-4715 are similar to those of the common slow-rotating pulsars, even though this pulsar's magnetosphere and surface magnetic field are several orders of magnitude smaller than those of the general population. The pulsar radio emission mechanism must therefore be insensitive to these fundamental neutron star properties.