Other
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt........14m&link_type=abstract
Thesis (PhD). CORNELL UNIVERSITY, Source DAI-B 62/07, p. 3232, Jan 2002, 326 pages.
Other
7
Scientific paper
We present the results of several projects, all aimed at better understanding the population and properties of pulsars at high and low energies. We first examine the flux variability of unidentified gamma-ray sources detected with the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory (CGRO). Comparison of variabilities with those of identified sources allows us to classify unidentified sources as pulsars, active galactic nuclei or other objects. In addition, we find an excess of variable, unidentified sources at low latitudes, suggesting that either pulsars can produce variable gamma rays under special circumstances or that a new class of Galactic gamma-ray sources exists. We then describe our likelihood analysis used to constrain the luminosity law for gamma- ray pulsars and some pulsar population parameters. We estimate how many unidentified EGRET sources are pulsars and also predict the gamma-ray pulsar population which the proposed Gamma-Ray Large Area Space Telescope (GLAST) will detect. While the Geminga pulsar is one of the strongest gamma- ray pulsars, it has weak or non-existent radio emission. In order to better understand the relationship between low and high-energy pulsar emission, we searched for Geminga in the radio with the Very Large Array. We present a sensitive upper limit, which accounts for the role of interstellar scintillation in modulating the pulsar flux. We also present a Bayesian technique for calculating the flux in a pulsed signal of unknown width and phase. Our non-detection of Geminga in the radio further supports the idea that many of the unidentified EGRET sources are also radio-quiet or radio-weak pulsars. We have also searched for radio pulsations from the X-ray point source near the center of Cassiopeia A detected by the Chandra X-Ray Observatory. No convincing signatures of a dispersed, periodic source or of isolated dispersed pulses were found, suggesting that this source belongs to the growing population of young neutron stars that are radio quiet or radio-weak. In addition to searches for radio counterparts to high- energy sources, we have carried out untargeted searches for new radio pulsars. The period and period derivative of one of these new pulsars, PSR J1740 + 1000, imply a spin-down age that is smaller than 95% of all known pulsars. The youth and proximity of this pulsar make it a good candidate for detection at X-ray and gamma-ray energies. We also discuss the possible high velocity of this pulsar, in light of its scintillation properties and position behind the North Polar Spur. As a part of this and other radio pulsar searches, we have conducted searches for single, dispersed pulses. We describe the abilities of this type of search to detect pulsars not detectable through a standard periodicity search. Results are presented for PSR B0540-69, the spiral Galaxy M33, some other galaxies, and for many known pulsars.
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