The NenuFAR Pulsar Blind Survey (NPBS): I. Survey overview, expectations, and first redetections

The NenuFAR Pulsar Blind Survey (NPBS) is an all-sky survey, searching for pulsars at radio frequencies below 85 MHz with the NenuFAR radio telescope. Taking into account the turnover at low frequencies in the pulsar spectra and the widening of their emission cone towards low frequencies, we expect approximately 8–20 not already discovered pulsars to be detectable by this survey, most of which are likely to be non-standard pulsars or pulsars in unusual parts of the P − Ṗ diagram (such as, e.g. slow pulsars). According to our simulations, we expect the discovered pulsars to feature spectra with spectral indices ≲ −3.2 and low turnover frequencies <<85 MHz. Conversely, a non-detection would give valuable clues as to the population of pulsars in this region of the parameter space. The current first stage of the survey observes declinations above 39° in the frequency range 39–76 MHz. A frequency-averaged sky coverage of 98% is reached by observing 7692 pointings of about 1.5° of radius in 27 min each. The observing programme started in August 2020, and is expected to be completed during 2024. Approximately a third of the data are currently being processed using a search pipeline based on PRESTO with some adaptations to low frequencies. Because of the high scatter broadening and the coarse time resolution, the NPBS searches for pulsars with periods from 30 ms to 30 s and dispersion measures (DMs) between 1 and 70 pc cm −3 . In the processed data, 24 known pulsars have been searched in order to verify the observing setup and the search pipeline. Seven of these pulsars have been detected, with DMs between 5 and 42 pc cm −3 . The related candidates have periods between 40 ms to 3.5 s, including candidates corresponding to harmonics. Of the seven, six correspond to the most intense pulsars of the set. The last detection is presumably due to a beneficial effect of the scintillation. Based on the faintest detection, the expected minimum signal-to-noise ratio for detecting a pulsar is 4.8, corresponding to a minimum flux of 6.9 mJy in the coldest regions of the sky.