ASTERIX

ASTERIX is the most recent addition to the array of pulsar instruments at the Effelsberg 100-m radio telescope. The instrument features an 8-bit analog-to-digital converter, clocking at or below 1024 MHz. This allows the sampling of analogue bands as large as 512 MHz. The sampled signal is then digitally processed on a high performance FPGA platform (ROACH board), to produce up to 32 subbands. A cluster of high performance computers attached to the ROACH board can either record the baseband data, or coherently dedisperse and fold the pulsar signal in realtime.

The flexibility of the instrument design makes it an excellent facility to carry out a wide range of science with pulsars. Monitoring the long term rotational stability of pulsars is one such experiment that has fantastic payoffs. In this context, the instrument is currently the default pulsar timing instrument at the Effelsberg telescope. The 8-bit digitisation, wide bandwidth, and the possibility to deal with radio frequency interference results in ASTERIX producing pulse profiles with higher signal-to-noise and time-of-arrivals with higher precision than the previous instruments. This greatly improves the already high quality and broad range of results capable with the Effelsberg 100-m telescope.

The baseband mode of the instrument permits its use in the LEAP project. Rapid transfers of the large volumes of data acquired in this mode is facilitated by the 10GbE network in the computer cluster. The baseband mode is also used in research that relies on high time resolution single pulses, as in understanding pulsar's emission mechanism i.e giant pulse emission from the Crab pulsar or PSR B1937+21.

ASTERIX's modular system design has thus resulted in a flexible and scalable instrument enabling a wide variety of pulsar projects at the telescope. Recently the instrument was scaled up with two more ROACH boards, and 16 high performance compute nodes to accomodate the increased bandwidth offered by the UBB front end. The incremental improvement, rapid prototyping and final development of the ASTERIX system is made possible by the availability of the high-performance CASPER hardware (ROACH board and iADC board) and the ease of programming these devices brought about by the CASPER libraries, Matlab and Xilinx System Generator.

Fig. 1: Simplified block diagram of the recent pulsar instruments at the Effelsberg 100-m radio telescope. The ASTERIX system is shaded gray in the figure. Computing and storage resources are shared by other pulsar instruments as well. Zoom Image
Fig. 1: Simplified block diagram of the recent pulsar instruments at the Effelsberg 100-m radio telescope. The ASTERIX system is shaded gray in the figure. Computing and storage resources are shared by other pulsar instruments as well. [less]
Fig. 2: CASPER ROACH board v1.00, based on a Virtex-5 FPGA. Zoom Image
Fig. 2: CASPER ROACH board v1.00, based on a Virtex-5 FPGA.
Fig 3.: CASPER iADC board, with Dual, 8-bit, 1 Gigasample/s ADC Zoom Image
Fig 3.: CASPER iADC board, with Dual, 8-bit, 1 Gigasample/s ADC
 
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