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Session 111 - Pulsars.
Display session, Saturday, January 10
Exhibit Hall,
We present sub-microsecond time resolution observations of the bright millisecond pulsar PSR J0437-4715 taken simultaneously at 660 MHz, 1380 MHz and 2290 MHz. Our data suggest that the giant ``micropulses'' reported for this pulsar are not canonical giant pulses such as those from the Crab pulsar or PSR B1937+21. They instead appear to be the high-amplitude end of a normal pulse distribution. The individual pulse widths demonstrate an inverse correlation with pulse amplitude similar to the Vela pulsar.
Further results do not support the claim that a diffraction pattern can be resolved in the phase distribution of strong pulses from PSR J0437-4715. If such a diffraction pattern were real, it should be visible in mean profiles of so-called ``micropulses'' averaged over the same number of pulses over which the diffraction pattern was observed. Our data, however, consistently produce smooth pulse profiles when averaged over the same number of these micropulses. A power spectrum analysis of pulse arrival phase -- similar to that employed by Ables, et al. (ApJ, 475:33L, Jan 1997) in their 327 MHz observations -- fails to confirm the periodicity that they report.
The data were obtained with S2 VLBI tape recorders at three telescopes simultaneously, with full polarization information recorded over a 16 MHz bandwidth. We then used a new capability of the S2 playback system to transfer the data directly into a computer for further processing with 60 ns time resoultion. Our data provide a unique opportunity for the investigation of pulse emission effects across a wide range of frequencies.
