Searching for pulsars with LOFAR

The main thrust of this thesis is the search for radio pulsars using the Low Frequency Array (LOFAR). LOFAR is part of a new generation of radio telescopes leading up to the building of the Square Kilometer Array. LOFAR uses a multitude of inexpensive antennas whose signals are combined digitally to create many sensitive, fully steerable, beams on the sky. As part of LOFAR's commissioning we performed two radio pulsar surveys, the LOFAR Pilot Pulsar Survey (LPPS) and the LOFAR Tied-Array Survey (LOTAS). The former survey put a limit on the fast radio transient rate and re-detected 65 pulsars, while the latter re-detected 27 pulsars and discovered 2 new ones. These discoveries bode well for future, more sensitive, pulsar surveys using LOFAR. We also describe extensions to standard single-pulse search techniques.
This thesis furthermore describes two smaller projects; attempts to detect pulsars as binary companions to subdwarf-B stars and an attempt to detect pulsed radio emission from the nearby pulsar Geminga. We were able to exclude pulsed radio emission from the sdB binary companions to a high degree of certainty. Our very sensitive observation of Geminga failed to detect pulsed radio emission, despite earlier claims. We conclude that those earlier detections were likely spurious, but leave open the possibility that Geminga is an intermittent radio source that turned off.