No abstract
The VSOP mission is a Japanese-led project to image radio sources with sub-milliarcsec resolution by correlating the signal from the orbiting 8-m telescope, HALCA, with a global array of telescopes. Twenty-five percent of the scientific time of this mission is devoted to a survey of 402 bright, small-diameter extra-galactic radio sources at 5 GHz. The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure; to provide a source list for use with future space VLBI missions; and to compare radio properties with other data throughout the EM spectrum. This paper describes: the compilation of a complete list of radio sources associated with active galactic nuclei (AGN); the selection of the subsample of sources to be observed with VSOP; the extensive ground resources used for the Survey; the status of the observations as of 2000 July; the data-analysis methods; and several examples of results from the VSOP Survey. More detailed results from the full sample will be given in future papers.
Abstract. The S2 baseband processing system (S2-BPS) is designed for a variety of pulsar measurements such as ultrafast signal fluctuations and pulse timing. Its key features are: the S2 recorder; the S2 Tape-to-Computer Interface (S2-TCI) which provides an efficient high data rate transfer from S2 tapes to computer; and the tightly coupled control interface to the computer which enables automated data transfer and processing. Developed originally for VLBI applications, the S2 recorder is based on the use of commercial VHS tape transports (VCR's), modified for use in digital high density, high data rate applications. A single S2 recorder "tape-set" of eight SVHS tapes provides up to 500 GBytes of data storage, and an unattended operating time of up to 8.5 hours at the maximum data rate of 128 Mbits/s or 16 MBytes/s, corresponding typically to 16 MHz bandwidth in two circular polarizations at 2-bit quantization, which generates a data rate of up to 1 GByte/minute. With 16 MHz individual record channels, a single S2 yields a sample time resolution of 31 ns. For more challenging applications, multiple S2's may be used for increased bandwidth and higher time resolutions. In this paper, we present an overview of the S2 baseband processing system and plans for future implementations of the system, and demonstrate first results of Vela pulsar recordings at Parkes in September 1995. We pay specific attention to the S2-TCI, a system designed to transfer S2 recorded data from tape to computer memory (RAM) via direct memory access (DMA). Computer data may be processed locally or sent to a more powerful "remote" (super) computer for processing.
The phase-coherent recording of pulsar data and subsequent software dispersion removal provide a flexible way to reach the limits of high time resolution, useful for more precise pulse timing and the study of fast signal fluctuations within a pulse. Because of the huge data rate and lack of adequate recording and computing capabilities, this technique has been used mostly only for small pulsar data sets. In recent years, however, the development of very capable, reasonably inexpensive high-speed recording systems and computers has made feasible the notion of pulsar baseband recording and subsequent processing with a workstation/computer. In this paper we discuss the development of a phase-coherent baseband processing system for radio pulsar observations. This system is based on the S2 VLBI recorder developed at ISTS/York University in Toronto, Canada. We present preliminary first results for data from the Vela pulsar, obtained at Parkes, Australia, and processed at ISTS/York University, and discuss plans for future developments.
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