The radio detection of atmospheric particle showers initiated by ultra-high energy cosmic rays is today a proven technique that allows to reconstruct their properties (direction of arrival, energy, nature). Among the precursors of this method, the CODALEMA experiment installed at the Nancay radio-astronomy Observatory has contributed to several major technological innovations relevant for the radio detection technique (autonomous triggering, hybrid reconstruction, very wide frequency bands) and its high-performance antennas are also used on the NenuFAR radio telescope in Nancay. We propose to exploit the unique environment of the Nancay Observatory through the CODALEMA experiment and the NenuFAR radio-telescope to explore the possibilities of radio-detection of atmospheric showers initiated by very high energy photons. The central idea is to phase a large set of antennas (several tens) in the direction of known sources emitting gamma (catalogs H.E.S.S., MAGIC, VERITAS, Fermi-LAT ...) to significantly increase the sensitivity of detection and to use the triggering capabilities on ultra fast transients controlled within the framework of CODALEMA. This would make it possible to observe the sources with a useful cycle close to 100 %. We present here the intended instrumental scheme as well as the expected signal level and some first results obtained on the observation of cosmic ray air showers with NenuFAR.

Cutting edge astrophysical studies require more and more observing time at low-frequency radio telescopes, which is limited and quite expensive. Modern digital signal processing systems still unable to provide affordable computational and storage resources to allow simultaneous beamforming in a wide frequency range for multiple studies. Low-frequency radio telescopes of a new generation are very flexible and could be split into subarrays or groups of subarrays for some studies which do not require large antenna effective area and high directivity. In this paper we make a survey of astrophysical studies in the frequency range 8-80 MHz using a rather small part of the low-frequency radio telescope GURT - the subarray of 25 active antennas.

R. Dallier∗1,2, L. Bondonneau5, D. Charrier1,2, A. Coffre2, S. Corbel2,4, L. Denis2, C. Dumez-Viou2, A. Escudie1, D. García-Fernàndez1, J. Girard4,3, J.M. Grießmeier5,2, L.V.E. Koopmans6, A. Loh3, L. Martin1,2, M. Pandey-Pommier2, B. Revenu1,2, P. Zarka2,3 1SUBATECH, Institut Mines-Telecom Atlantique CNRS Université de Nantes, Nantes, France 2Station de radioastronomie de Nançay, CNRS/Observatoire de Paris PSL Université d’Orléans/OSUC, Nançay, France 3LESIA, Observatoire de Paris, CNRS, PSL, SU/UP/UO, Meudon, France 4AIM/CEA Paris-Saclay, Université Paris Diderot, CNRS, Gif-sur-Yvette, France 5LPC2E Université d’Orléans/CNRS, Orléans, France 6Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands

The “8th International Workshop on Planetary, Solar and Heliospheric Radio Emissions” was held in October 2016 in the historical castle Schloss Seggau, about 35 km south of Graz, Austria. The proceedings of this workshop are now available as the book Planetary Radio Emissions VIII (PRE VIII), which is a continuation of the “PRE silver series” issued by the Austrian Academy of Sciences Press. All contributions were peer-reviewed under the guidance of the four editors. For more than three decades the developments in the field of planetary and solar radio emissions have been documented in the PRE proceedings. The new volume PRE VIII contains articles about the first observations from the Juno spacecraft, which started to orbit Jupiter in mid-2016, and articles analysing the data of Cassini, whose mission ended in September 2017. A large number of contributions deals with the topic of Jovian radio emissions, where the ground-based support of space missions has become increasingly important, and where the statistical analysis of years of data have led to new conclusions about the influence of the Galilean moons. The large ground-based radio telescopes (LOFAR, UTR-2, GURT, LWA, NDA and others) have other important scientific targets besides Jupiter, namely the Sun and exoplanets. The articles about exoplanets in PRE VIII give the impression that a first detection of radio emission signatures could happen in a not too distant future. Other contributions deal with terrestrial radio emissions and theory. Finally, the technical developments in instrumentation have led to the discovery of new fine structures in radio emissions or to improved solar radio imaging, and newly developed databases should make radio data available to all interested scientists around the globe.

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.

Jupiter is a complex and at the same time very powerful radio source in the decameter wavelength range. The emission is anisotropic, intrinsically variable at millisecond to hour timescales, and also modulated by various external processes at much longer periods, ranging from ~10 h to months or years (including Jovian day and year, solar activity and solar wind variations, and for ground-based observations, terrestrial day and year). As a consequence, long-term observations and their statistical study have proved to be necessary for disentangling and understanding the observed phenomena. We have built a database from the available 26 yr of systematic, daily observations conducted at the Nançay Decameter Array and recorded in digital format. This database contains all observed Jovian decametric emissions, classified with respect to the time-frequency morphology, their dominant circular polarization, and maximum frequency. We present the results of the first statistical analysis of this database. We confirm the earlier classification of Jovian decameter emissions in Io-A, -A′, -B, -C, -D and non-Io-A, -B, -C types, but we also introduce new emission types (Io-A′′ and Io-B′) and precise and characterize the non-Io-D type. We determine the contours of all emission types in the CML− ΦIo plane (Central Meridian Longitude in Jupiter’s System III coordinates versus Io Phase), provide representative examples of their typical time-frequency patterns, and the distribution of emission’s maximum frequency as a function of ΛIo (Io’s Longitude). Finally, we present a statistical analysis of the distributions of the occurrence rate, duration, intensity and polarization for each emission type. non-Io-DAM appears to be related to small-scale, possibly bursty auroral structures.

The current status of the large decameter radio telescope UTR-2 (Ukrainian T-shaped Radio telescope) together with its VLBI system called URAN is described in detail. By modernization of these instruments through implementation of novel versatile analog and digital devices as well as new observation techniques, the observational capabilities of UTR-2 have been substantially enhanced. The total effective area of UTR-2 and URAN arrays reaches 200 000 m2, with 24 MHz observational bandwidth (within the 8–32 MHz frequency range), spectral and temporal resolutions down to 4 kHz and 0.5 msec in dynamic spectrum mode or virtually unlimited in waveform mode. Depending on the spectral and temporal resolutions and confusion effects, the sensitivity of UTR-2 varies from a few Jy to a few mJy, and the angular resolution ranges from ~ 30 arcminutes (with a single antenna array) to a few arcseconds (in VLBI mode). In the framework of national and international research projects conducted in recent years, many new results on Solar system objects, the Galaxy and Metagalaxy have been obtained. In order to extend the observation frequency range to 8–80 MHz and enlarge the dimensions of the UTR-2 array, a new instrument – GURT (Giant Ukrainian Radio Telescope) – is now under construction. The radio telescope systems described herein can be used in synergy with other existing low-frequency arrays such as LOFAR, LWA, NenuFAR, as well as provide ground-based support for space-based instruments.

In the frame of the preparation of the NASA/JUNO and ESA/JUICE (Jupiter Icy Moon Explorer) missions, and the development of a planetary sciences virtual observatory (VO), we are proposing a new set of tools directed to data providers as well as users, in order to ease data sharing and discovery. We will focus on ground based planetary radio observations (thus mainly Jupiter radio emissions), trying for instance to enhance the temporal coverage of jovian decametric emission. The data service we will be using is EPN-TAP, a planetary science data access protocol developed by Europlanet-VESPA (Virtual European Solar and Planetary Access). This protocol is derived from IVOA (International Virtual Observatory Alliance) standards. The Jupiter Routine Observations from the Nancay Decameter Array are already shared on the planetary science VO using this protocol. Amateur radio data from the RadioJOVE project is also available. We will first introduce the VO tools and concepts of interest for the planetary radioastronomy community. We will then present the various data formats now used for such data services, as well as their associated metadata. We will finally show various prototypical tools that make use of this shared datasets. A preliminary study based on January-February 2014 data will also be presented.

This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. Since 1998, digital receivers performing on-the-fly dynamic spectrum calculations or waveform data recording without data loss have been used at the UTR-2 radio telescope, the URAN VLBI system, and the GURT new generation radio telescope. Here, we detail these receivers developed for operation in the strong interference environment that prevails in the decameter wavelength range. Data collected with these receivers allowed us to discover numerous radio astronomical objects and phenomena at low frequencies, a summary of which is also presented.

NASA/JUNO and ESA/JUICE (Jupiter Icy Moon Explorer) missions, and the development of a planetary sciences virtual observatory (VO), we are proposing a new set of tools directed to data providers as well as users, in order to ease data sharing and discovery. We will focus on ground based planetary radio observations (thus mainly Jupiter radio emissions), trying for instance to enhance the temporal coverage of jovian decametric emission. The data service we will be using is EPN-TAP, a planetary science data access protocol developed by Europlanet-VESPA (Virtual European Solar and Planetary Access). This protocol is derived from IVOA (International Virtual Observatory Alliance) standards. Data from all major decametric radio instruments will contribute: Nançay Decameter Array (France), LOFAR (France, Sweden, Poland), NenuFAR (France), URAN (Ukraine), LWA (USA), Iitate Radio Observatory (Japan), etc. Amateur radio data from the RadioJOVE project is also available. The attached figure shows data from those three providers. We will first introduce the VO tools and concepts of interest for the planetary radioastronomy community. We will then present the various data formats now used for such data services, as well as their associated metadata. We will finally show various prototypical tools that make use of this shared datasets.

The low frequency radio astronomy (decameter-meter range, frequencies of 10-300 MHz) currently demonstrates rapid progress all over the world. New generations of large antennas - LOFAR, LWA, MWA and others - have been created in many countries. At the same time Ukrainian radio astronomical systems UTR-2 and URAN still remain the largest and most informative ones at the lowest frequency range available for the ground-based radio astronomy (below 33 MHz), especially after their radical modernization during the most recent years. A great number of top priority results have been obtained on the basis of these radio telescopes. The results prove a high significance of the low frequency radio astronomy for astrophysics. Substantial part of these results have been obtained in the course of many year cooperation between Ukraine on one side and France, Austria, Germany and other countries on the other. Creation of new low frequency instruments GURT (Ukraine) and LSS/NenuFAR (France) for the wide frequency range of 10-80 MHz opens up new possibilities for research and fruitful cooperation.

Saturn Electrostatic discharges (SED) are sporadic broadband impulsive radio bursts associated with lightning in Saturnian atmosphere. After 25 years of space investigations in 2006 the first successful observations of SED on the UTR-2 radio telescope were carried out [1]. Since2007 along-term program of ED search and study in the Solar system has started. As a part of this program the unique observations with high time resolution were taken in 2010. New possibilities of UTR-2 radio telescope allowed to provide a long-period observations and study with high temporal resolution. This article presents the results of SED study in a wide range of time scales: from seconds to mi­croseconds. For the first time there were obtained a low frequency spectrum of SED. We calculated flux densities of individual bursts at the maximum achievable time resolu­tion. Flux densities of most intensive bursts reach 4200 Jy.