8th HEAD Meeting, 8-11 September, 2004
Session 25 X-ray Binaries and White Dwarfs
Poster, Friday, September 10, 2004, 9:00am-10:00pm

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[25.15] Deep Searches for Coherent Pulsations from Low Mass X-ray Binaries

P. Ray (NRL), R. Dib, S. Ransom, V. Kaspi (McGill)

An evolutionary link between Low Mass X-ray Binaries (LMXBs) and Low Mass Binary Pulsars (LMBPs) has long been proposed. Before the launch of RXTE, the critical missing piece of evidence was the detection of coherent millisecond pulsations from LMXBs that would confirm their millisecond spin rates and essentially confirm the connection. After numerous fruitless searches with previous instruments such as Ginga and EXOSAT, this search was a primary motivation for RXTE. Now, coherent millisecond pulsations have been detected, but all of those are in transient, low accretion rate, ultracompact binary systems, not in the bright persistent LMXBs, despite the fact that they are clearly spinning with millisecond periods based on the oscillations seen during X-ray bursts. The key questions now are what is this lack of pulsations telling us about these systems and what makes the detected systems such comparitively strong pulsators. We are performing a deep search for coherent pulsations in the catalog of well observed LMXBs in the RXTE archive. We are employing a new search technique that greatly enhances the detectability of faint pulsations in short period binary systems. This search will push the pulsed fraction limits down to better than 0.8% in most cases, as compared to the ~5% pulsed fractions observed in the five known accreting millisecond pulsars. This search will either discover pulsations from the bright LMXBs or set stringent limits for comparing with theories of how such pulses are hidden.

This work is supported in part by NASA ADP03-0029-0113.

The author(s) of this abstract have provided an email address for comments about the abstract: Paul.Ray@nrl.navy.mil

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.