What is LOFAR?


The Low Frequency Array (LOFAR) is an observatory sensitive to the radio portion of the electromagnetic spectrum. LOFAR is made up of antennas which are clustered into stations. One of these stations, called I-LOFAR, is in Ireland. It is situated on the grounds of Birr Castle, near the Leviathan. There are two kinds of antennas: the High Band Antennas (HBA) and the Low Band Antennas (LBA). Both antennas are sensitive to different frequencies of radiation and require different configurations to operate.

LOFAR Science


There are six LOFAR key science projects:

  -   Search for redshifted 21 cm line emission from the epoch of reionization.
  -   Conduct large sky surveys.
  -   Hunt for transient radio phenomena and pulsars.
  -   Uncover the origin of high-energy cosmic rays.
  -   Examine the evolution of cosmic magnetic fields.
  -   Study the Sun and monitor space weather.

The High Energy Astrophysics Group at UCD are members of the of the LOFAR Surveys Key Science Project (KSP). The goal of this KSP is to survey the entire northern hemisphere sky with LOFAR, first with the Dutch HBA stations and then with the international stations and the LBA. These sky surveys are possible thanks to the sensitive, widefield, high resolution capabilities of LOFAR. The first data release of the LOFAR Two Metre Sky Survey (LoTSS) was released in February 2019. This video shows some of the highlights from this data release.

I-LOFAR


LOFAR stations are situated throughout Europe with the core stations located in the Netherlands. There is also a station in Ireland. The distance between the Irish station and a Polish station form the longest baseline at 1,900 km. This is useful since the length of the baselines determine the resolution of the telescope, with the longest baselines giving the highest resolution. The station in Ireland is in Co. Offaly, which makes an excellent site due to the minimal radio frequency interference. For more information, see the Irish LOFAR website.

The Irish LOFAR station was constructed during the summer 2017, and several people from UCD were involved with the build. The High Energy Astrophysics Group are also active members of the I-LOFAR Consortium and routinely make observations with the station.

The LOFAR stations stretch throughout Europe. The station being constructed at Birr in Ireland will extend the size of the array. (credit: ASTRON)

Computing


LOFAR generates enormous quantities of data which poses many major challenges. Supercomputers are required to analyse the data and high data transfer rates are necessary to transport the data from the stations across Europe back to the Netherlands. The computing is managed by the Netherlands Institute for Radio Astronomy (ASTRON). For more information about the technical aspects of the LOFAR computing facilities, see the ASTRON website.

LOFAR at University College Dublin


At UCD, we are using LOFAR to study the low frequency properties of blazars in great detail (e.g. Mooney et al., 2019). Blazars are a type of active galactic nuclei which have a relativistic jet inclined at a small angle to our line of sight. By using LOFAR, we can search for diffuse emission around these objects to constrain their morphology. Acquiring data about the blazars at low frequencies allows us to develop an understanding of the underlying physical processes taking place in the jet. LOFAR offers a new window through which to study blazars and other extreme extra-galactic objects and at UCD the longest baselines are used to maximise this opportunity.