The Low-Frequency Beamformer and Imager NenuFAR

NenuFAR (New extension in Nançay upgrading LOFAR), is a low-frequency SKA pathfinder presently in construction and commissioning in Nançay (France) [1], [2]. NenuFAR consists of 102 mini-arrays (MA) of 19 dual polarization antennas each. 96 MA cover densely a disk (core) of 400m in diameter, and 6 MA are located at distances up to ∼3 km. NenuFAR will cover the range 10–85 MHz, that encompasses the low-frequency range of LOFAR ([3] 0–80 MHz nominal, that can be extended to 10–85 MHz), and be three instruments in one: (i)the core, connected to the receivers of the French LOFAR (FR606) station, will form a giant LOFAR station that can replace the LOFAR FR606 LBA field and be used as part of LOFAR; this LOFAR Super Station (LSS) will improve the sensitivity of long baselines by over one order of magnitude and thus the quality of high angular resolution (sub-arcsecond) imaging at low frequencies with LOFAR. (ii)the core will simultaneously be a standalone compact beamformer providing high instantaneous sensitivity, that will allows us to search efficiently for weak unresolved sources such as pulsars, exoplanets, stars … A dedicated pulsar/time/frequency backend is in development, and the possibility to connect a SETI receiver that will analyze all NenuFAR data in piggyback (commensal) mode is under study. (iii)finally, thanks to the addition of a GPU-based correlator, NenuFAR will also (and simultaneously) be a standalone imager that can be used in two modes: a fast (1 sec) coarse resolution (1°) mode, using the 96 MA of the core only, and a slow (6–8 hours) medium resolution (∼8’) mode using all the 102 MA, core + distant; this mode will enable imaging studies in cosmology (search for the dark ages / cosmic dawn signal), planetary and stellar physics (exoplanets, stars and their plasma interactions), and the study of galaxies, clusters and haloes.