The Astrophysics team, thanks in particular to Ismaël Cognard’s instrumental expertise, has got a long experience in developing several generations of instrumentations dedicated to the precise timing (at a level of a few tens of nanoseconds) of pulsars in radio. The technique consists in correcting in real time, in the flow of data arriving at the telescope, the dispersion effect caused by the interstellar medium. This results in a chromatic delay in 1/f^2, where f is the radio frequency of observation. The pulsar instrumentation also allows the signal to be integrated in real time, in phase with the apparent rotation of the pulsar, and thus to be detected with exposure times of a few seconds to a few minutes. The first instrumental module was analog and used a sweeping oscillator whose signal, mimicking dispersion, was mixed with the astrophysical signal (1990s). Since 2004, the new generations of instrumentations have been digital, based on a hybrid architecture, combining broadband analog-to-digital converters and different types of calculators: FPGA (Field-Programmable Gate Array), CPU (processors) and GPU (graphics cards). After detection and digitization, the broadband signal is split into channels, de-dispersed and then integrated in frequency and time. The current generation allows the analysis of a bandwidth of 2 GHz with NRT or 2×75 MHz with NenuFAR.
The NUPPI (NRT) or LUPPI (NenuFAR) codes are developed in C and CUDA languages by (and under the direction of) Ismaël Cognard. They control in real time the complex digital instrumentation and produce high-quality data. These codes are based on the GUPPI code designed for the Green Bank Telescope (GBT). They are maintained by the team and are constantly evolving.
- Max Planck Institut für Radioastronomie, Bonn (Germany)
- University of Manchester (United Kingdom)
- Cagliari Observatory (Italy)
- Netherlands Institute for Radioastronomy (ASTRON), Dwingeloo (Netherlands)
- Laboratoire AstroParticule et Cosmologie (APC), Paris
- Centre d’Etudes Nucléaires de Bordeaux Gradignan (CENBG), Gradignan
- Naval Research Laboratory (NRT, US)
- Stanford Linear Accelerator Center (SLAC, US)