European Pulsar Timing Array

The European Pulsar Timing Array (EPTA) is a European collaboration to combine five 100-m class telescopes to observe an array of pulsars with the specific goal of detecting gravitational waves. It competes with the Australian and American pulsar timing arrays, the Parkes Pulsar Timing Array and the North American Nanohertz Observatory for Gravitational Waves.

Pulsars and TOA's

Pulsars are rapidly rotatating, highly magnetized neutron stars that emit radio waves from their magnetic poles that are observed as pulses. The time of arrival (TOA) of these pulses are known for their stability. A special class of pulsars, called millisecond pulsars (MSP), even compete with the accuracy of atomic clocks. Keeping track of the TOA's of different MSP's over the sky allows for high-precision timing experiments which can even be used to detect one of the holy grails of physics: gravitational waves.

Detection of gravitational waves

Gravitational waves (GW) are small disturbances in space-time, caused by the motion of masses. These waves are so weak that only the strongest waves, caused by rapid motion of dense stars or black-holes, have a chance of being detected. A pulsar timing array (PTA) uses an array of MSP's as the endpoints of a galaxy-scale GW detector. It is sensitive to GW's with a frequency in the nano-Hertz regime, which corresponds to the regime of the stochastic GW background caused by the coalescence of super-massive black holes in the early universe. This makes PTA's complimentary to other GW detectors such as LIGO, VIRGO and LISA.

Telescopes

The EPTA uses five European telescopes. These are the Westerbork Synthesis Radio Telescope, the Effelsberg Radio Telescope, the Lovell Telescope, the Nancay Radio Telescope and the Sardinia Radio Telescope.

LEAP

Recently the EPTA has made a giant "leap" forward thanks to European funding of the Large European Array for Pulsars (LEAP). This project involves coherently combining the five EPTA-telescopes to make the equivalent of a fully steerable 194-m dish. This will improve the TOA's by an order of magnitude, possibly leading to a first detection of GW's around 2015.