As part of a large-scale search for coherent pulsations from LMXBs in the RXTE archive, I have completed a detailed series of searches for coherent pulsations of 4U 1820--30---an ultracompact LMXB with a binary period of 11.4 minutes located in the globular cluster NGC 6624. The small binary period leads to a very high acceleration, so I used phase modulation searches as well as acceleration searches to give significant sensitivity to millisecond pulsations. I searched a total of 34 archival RXTE observations, 32 of which had an on-source integration time longer than 10 ks, and some of which were made consecutively which allowed me to combine them. While I found no pulsations, I have been able to place the first stringent (95% confidence) pulsed fraction limits of ≲ 0.8% for all realistic spin frequencies (i.e. ≲ 1 kHz) and likely companion masses (0.02 M⊙ ≤ Mc≤ 0.3 M⊙ ). By contrast all five LMXBs known to emit coherent pulsations have intrinsic pulsed fractions in the range 3% to 7% when pulsations are observed.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.80253 |
| Date | January 2003 |
| Creators | Dib, Rim |
| Contributors | Kaspi, Victoria M. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Physics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002095286, proquestno: AAIMQ98622, Theses scanned by UMI/ProQuest. |
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