Pulsar Discoveries and their Exploitation

Abstract

Pulsars are the rapidly-rotating, highly-magnetized, neutron star remnants of the supernova explosions of massive stars. Pulsars have been used in a wide variety of studies of astronomy and physics. Of the >2500 pulsars now known, most were found in blind, large-scale searches at radio frequencies. The PALFA survey at the Arecibo Observatory is an example of this type of search. I present details of the PALFA data analysis software that I designed, which has already been used to discover 40 pulsars, bringing the total number of discoveries in the survey to 144 pulsars. Additionally, I implemented a novel technique for reliably measuring the survey’s sensitivity in the presence of terrestrial interference and red noise. The sensitivity determined with my technique agrees with theoretical predictions for millisecond-period pulsars (MSPs), but is reduced for long-period (P ∼ > 100 ms) pulsars. Simulations suggest that this reduction in sensitivity should result in 33 ± 3% fewer detections than expected, which corresponds to 224 ± 16 pulsars detected, given the observations to date. This result is consistent with the 241 pulsars actually detected. In general, pulsar timing analyses based on long-term monitoring campaigns are extremely productive scientifically. My collaborators and I conducted such an analysis for PSR J1952+2630, a 20.7-ms pulsar in a binary system with a massive white dwarf companion, found in the PALFA survey. Our analysis made it possible to constrain the evolutionary history of the binary system and the composition of the pulsar’s companion. Furthermore, our simulations of future observations of PSR J1952+2630 indicate that this system will be useful in constraining theories of relativistic gravity in the next ∼10 years. To maximize the scientific potential of MSPs, Pulsar Timing Array (PTA) projects conduct long-term, large-scale observing campaigns with many of the world’s largest radio telescopes. For example, as part of the European Pulsar Timing Array (EPTA), the Effelsberg 100-m radio telescope regularly observes ∼50 MSPs with PSRIX, a new data recording instrument installed in 2011. The first four years of these data have been reduced with the automated software that I developed. By comparing the PSRIX data with results from the previous instrument, the Effelsberg-Berkeley Pulsar Proces- sor, I found that PSRIX provides significantly greater sensitivity. With this increased sensitivity, I estimated the improvement in our chances of detecting the low-frequency gravitational wave background (GWB) with MSPs, one of the main goals of PTAs. A major obstacle to this detection is the effect of interstellar medium variations. With this in mind, I conducted observations at 5 and 9 GHz with PSRIX and showed that by pushing PTA observations to higher frequencies, it may be possible to mitigate this source of noise and further enhance the sensitivity to the GWB. Observations from the EPTA have been combined with data from the International Pulsar Timing Array (IPTA) community to form the largest, most sensitive pulsar timing data set ever assembled. This unique data set has many diverse applications. For instance, I am using it to measure the masses of the Solar System planets. My on- going analysis already provides results consistent with previous studies, and thus can be used to verify the quality of the IPTA data set, a key first step towards exploiting its unrivalled sensitivity.