Context.NenuFAR (New extension in Nançay upgrading LOFAR) is a new radio telescope developed and built on the site of the Nançay Radio Observatory. It is designed to observe the largely unexplored frequency window from 10 to 85 MHz, offering a high sensitivity across its full bandwidth. NenuFAR has started its “early science” operation in July 2019, with 58% of its final collecting area.Aims.Pulsars are one of the major phenomena utilized in the scientific exploitation of this frequency range and represent an important challenge in terms of instrumentation. Designing instrumentation at these frequencies is complicated by the need to compensate for the effects of both the interstellar medium and the ionosphere on the observed signal. We have designed a dedicated backend and developed a complete pulsar observation and data analysis pipeline, which we describe in detail in the present paper, together with first science results illustrating the diversity of the pulsar observing modes.Methods.Our real-time pipeline LUPPI (Low frequency Ultimate Pulsar Processing Instrumentation) is able to cope with a high data rate and provide real-time coherent de-dispersion down to the lowest frequencies reached by NenuFAR (10 MHz). The full backend functionality is described, as the available pulsar observing modes (folded, single-pulse, waveform, and dynamic spectrum).Results.We also present some of the early science results of NenuFAR on pulsars: the detection of 12 millisecond pulsars (eight of which are detected for the first time below 100 MHz); a high-frequency resolution mapping of the PSR B1919+21 emission profile and a detailed observation of single-pulse substructures from PSR B0809+74 down to 16 MHz; the high rate of giant-pulse emission from the Crab pulsar detected at 68.7 MHz (43 events per minute); and the illustration of the very good timing performance of the instrumentation, which allows us to study dispersion measure variations in great detail.

ABSTRACT PAON4 is an L-band (1250–1500 MHz) small interferometer operating in transit mode deployed at the Nançay observatory in France, designed as a prototype instrument for intensity mapping. It features four 5 m diameter dishes in a compact triangular configuration, with a total geometric collecting area of ${\sim} 75\, \mathrm{m^2}$, and is equipped with dual polarization receivers. A total of 36 visibilities are computed from the eight independent RF signals by the software correlator over the full 250 MHz RF band. The array operates in transit mode, with the dishes pointed toward a fixed declination, while the sky drifts across the instrument. Sky maps for each frequency channel are then reconstructed by combining the time-dependent visibilities from the different baselines observed at different declinations. This paper presents an overview of the PAON4 instrument design and goals, as a prototype for dish arrays to map the large-scale structure in radio, using intensity mapping of the atomic hydrogen 21 cm line. We operated PAON4 over several years and use data from observations at different periods to assess the array performance. We present a preliminary analysis of a large fraction of these data and discuss crucial issues for this type of instrument, such as the calibration strategy, instrument response stability and noise behaviour.

The Nancay Decameter Array (NDA) routinely observes low frequency (10– 100 MHz) radio emissions of Jupiter and the Sun since 4 decades. The NDA observations, acquired with a variety of receivers with increasing performances, were the basis for numerous studies of Jovian and solar radio emissions and now form a unique long-term database spanning ≥ 3 solar cycles and Jovian revolutions. In addition, the NDA historically brought a fruitful support to space-based radio observatories of the heliosphere, to multi-wavelength analyses of solar activity and contributes to the development of space weather services. After having summarized the NDA characteristics, this article presents latest instrumental and database developments, some recent scientific results and perspectives for the next decade.

A full-time beam-former for two independent antenna groups, with visibility computation capabilities at a slower rate, have been formerly designed on a single FPGA for the BAO-radio instrument, a radio telescope demonstrator for the study of dark energy by HI probing technique. On the same FPGA, a firmware dedicated for the FAN project at the Nancay radio telescope have been designed, and can provide a full-time dual beam-forming on a single antenna group. It can process an incoming data flow of twelve channels organized each as complex spectrum (2×8bits) of 4096 frequency with a 4GbPS effective rate. The dual-beam capability of the system has been successfully tested on the FAN array with transits on CasA and 3C123 radio sources after a configuration by complex coefficients computed from previous off-line software correlations on CasA. Recently, another beam-forming on 3C123 has been done after a calibration on CasA performed by the beam-former set in correlation mode and a source-tracking.

Nancay radio astronomy station teams are involved in several aspects of the Research and Development (R&D) for radio astronomy detectors and systems:i) Microelectronics: Low Noise Amplifiers (LNA), receiver oil chip and system in package. The long-term goal is to provide sub-systems for the future Square Kilometer Array and its Pathfinders. A beamformer chip has been integrated in the FP6 SKADS dense aperture array technology demonstrator EMBRACE. Wide band SiCe LNAs are developed, beamformers with in-chip control are studied and more complex integrated receivers are designed for the european Aperture Array Verification Programme demonstrator.ii) Digital signal processing: EMBRACE beamforming has been implemented in the digital backend and RFI-mitigation oriented signal processing has been designed for realtime systems, including work for FP6 SKADS and FP7 PrepSKA.iii) A study of Phased Array Feeds has started in 2008, in order to study the radio electric properties of PAFs at the focus of large F/D telescopes, such as the Nancay Radio Telescope, as well as to test PAF systems in collaboration with the SPP/IRFU and LAL/IN2P3 laboratories.