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A. N. Lommen, D. C. Backer (UC Berkeley)
Using the high-frequency, wide-bandwidth capability of the Arecibo Telescope (1 GHz of bandwidth at 2.4 GHZ, and 2 GHz of bandwidth at 5 GHZ) we have studied the frequency evolution of pulse profiles over a large frequency range (4 GHz) and with unprecedented spectral resolution. New conclusions about millisecond pulsar emission geometry are made from these results. In addition, we present scintillation parameters for several millisecond pulsars at high frequency, and discuss the implications for improving timing accuracy via ``scintle hunting.''
In the second part of the talk, we will discuss the possibility of using what we call the ``Pulsar Timing Array" to detect long-wavelength gravitational radiation. In particular, we turn our attention toward the recent ~106d quasi-periodic flux variations in Sagittarius A* (Sgr A*) at radio wavelengths reported by Zhao, Bower, & Goss (2001, ApJL 547:L29). We consider what size effect such a system would have on timing residuals, if the variations were due to a binary black hole in Sgr A*. We have analyzed Arecibo Observatory arrival time data on PSRs J1713+0747 and B1937+21 for the expected perturbation by gravitational radiation with a ~53d period. No detection is made, as expected, based on the estimated level. We discuss future uses of the Pulsar Timing Array, including detecting the gravitational wave background from the early universe.