The Low Frequency Array (LOFAR) is a new-generation radio interferometer based in the north of the Netherlands with further stations across Europe. It will operate in the relatively unexplored frequency range 30-240 MHz. With its dense core and long baselines, LOFAR has unparalleled sensitivity and angular resolution in the low-frequency radio regime. LOFAR's capabilities make it an important pathfinder to the Square Kilometer Array (SKA).
LOFAR consists of 1000's of antenna grouped into stations across a large area thus creating the perfect tool for pulsar surveys. During the comissioning stages of LOFAR, 2 new pulsar discoveries were made leading to a full Northern sky survey. The LOFAR Tied-Array All Sky Survey(LOTAAS) began taking data 01 December 2012 and as of 29 January 2016 has almost completed the first out of three sparse coverage of the sky. The survey is expected to uncover over 1,000 pulsars in the Northern sky which will add significantly to the Galactic pulsar catalogue. 'Observing Pulsars and Fast Transients with LOFAR' - a paper published on the Astronomy & Astrophysics website contains more detailed information on the LOFAR pulsar survey.
Aerial view of the LOFAR core. (C) ASTRON
LOTAAS uses the 12 HBA substations of the LOFAR core to form three sub-array incoherent beams for each survey pointing that cover ~30 square degrees of the sky. Within each incoherent beam, a hexagonal grid of 61 tied-array beams are formed. The three sets of tied-array beams cover ~10 square degrees of the sky. The arrangement of the beams can be seen on the figure below. An additional 12 tied-array beams are formed for each incoherent beam to point towards any known pulsars that falls within the field of view of the incoherent beam but outside of the grid. This results in a total of 222 beams per survey pointing. The survey has a central observing frequency of 139 MHz with a bandwidth of 32 MHz, spectral resolution of 12kHz and sampling time of 492 μs. This generates data at a rate of 35 Gbps and each 1-hour pointing produces 16 TB of raw data.
The new increased sample of pulsars will add many new lines of sight through the Galaxy, which will be valuable for studying the ISM and Galactic magnetic field using dispersion and rotation measures. The newly discovered population will also be useful for studying pulsar birth rates, the velocities and distributions of pulsars and core collapse physics. It is also likely that several interesting new objects will be found, perhaps even the first pulsar-black hole binary which could be used to test General Relativity.
LOFAR will also be able to utilise long baselines (~100 km) in order to perform deep surveys with very high resolution. By looking at other galaxies with long integration times, it is likely that LOFAR will detect the first pulsar from another galaxy.