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Timing Noise in SGR 1806-20We have phase connected a sequence of Rossi X-ray Timing Explorer Proportional Counter Array observations of SGR 1806-20 covering 178 days. We find a simple secular spin-down model does not adequately fit the data. The period derivative varies gradually during the observations between 8.1 and 11.7 x 10(exp -11) s/s (approx. 40% larger than the long term trend), while the average burst rate as seen with the Burst and Transient Source Experiment drops throughout the time interval. The phase residuals show no evidence for periodicity, but more closely resemble timing noise as seen ill radio pulsars. The magnitude of the timing noise., however, is large relative to the noise level typically found in radio pulsars (Delta(sub 8) = 4.8; frequency derivative average power approx. = 8 X 10(exp -20) Hz/sq s). Combined with the noise levels measured for some AXPs. we find all magnetar candidates have A8 values larger than those expected from a simple extrapolation of the correlation found in radio pulsars. We find the timing noise ill SGR 1806-20 is greater than or equal to the levels found in some accreting systems (e.g., Vela X-1, 4U 1538-52 and 4U 1626-67). Alternatively, an orbital model with a period P(sub orb) = 733 days provides a statistically acceptable fit to the data. If the phase residuals are created by Doppler shifts from a gravitationally bound companion. then the allowed parameter space for the mass function (small) and orbital separation (large) rule out the possibility of accretion from the companion sufficient to power the persistent emission from the SGR.
Document ID
20000074665
Acquisition Source
Marshall Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Woods, Peter M.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Kouveliotou, Chryssa
(NASA Marshall Space Flight Center Huntsville, AL United States)
Finger, Mark H.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Gogus, Ersin
(NASA Marshall Space Flight Center Huntsville, AL United States)
Scott, D. Matthew
(NASA Marshall Space Flight Center Huntsville, AL United States)
Dieters, Stefan
(NASA Marshall Space Flight Center Huntsville, AL United States)
Thompson, Christopher
(North Carolina Univ. Chapel Hill, NC United States)
Duncan, Robert C.
(Texas Univ. Austin, TX United States)
Hurley, Kevin
(California Univ. Berkeley, CA United States)
Strohmayer, Tod
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 2000
Subject Category
Astronomy
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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