Pulsar Searches: From Radio to Gamma-Rays

Citation

Chandler, Adam Matthew (2003) Pulsar Searches: From Radio to Gamma-Rays. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/MDJX-M255. https://resolver.caltech.edu/CaltechETD:etd-01232003-213508

Abstract

We report the results of four different pulsar searches, covering radio, X-ray, and gamma-ray wavelengths. These searches targeted pulsars in virtually all of their guises: young and old, long-period and short-period, accretion-powered and rotation-powered. Ten new pulsars were discovered.

There are very few known gamma-ray pulsars, all of which were found by folding gamma-ray data with a pulse period known from other wavelengths. Some emission models indicate that there may be a large number of gamma-ray pulsars that are undetectable at lower energies. We searched several of the brightest unidentified gamma-ray sources for pulsations. This was the first attempt to identify gamma-ray pulsars by a direct search of gamma-ray data. No new identifications resulted and we report upper limits.

Even more rare than gamma-ray pulsars are accreting millisecond pulsars. We searched for coherent pulsations from Aql X-1, a low-mass X-ray binary suspected of harboring such an object. No pulsations were detected, and we argue that the quiescent emission of this system has a thermal origin (i.e., it is not due to low-level accretion).

The two radio searches included here were both designed to detect millisecond pulsars. First, we report the results of a large area survey from Arecibo. Five new slow pulsars were discovered, including an apparent orthogonal rotator and an extremely unusual bursting radio pulsar. No short-period pulsars were discovered and we place some of the first useful observational constraints on the limiting spin period of a neutron star.

We also performed pointed searches of several globular clusters using the new Green Bank Telescope. Three new binary millisecond pulsars were found in M62. These were the first new objects found with the GBT, and they bring the total pulsar population in M62 to six. We also discovered two isolated pulsars, one each in NGC 6544 and NGC 6624.

Many of the methods we developed will be relevant to future searches. Perhaps the most significant contribution is a dynamic power spectrum-based technique that finally allows sensitive searches for binary pulsars whose orbital periods are of the same order as the observation time.

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