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Large Torque Variations in Two Soft Gamma RepeatersWe have monitored the pulse frequencies of the two soft gamma repeaters SGR 1806-20 and SGR 1900+14 through the beginning of year 2001 using primarily Rossi X-Ray Timing Explorer Proportional Counter Array observations. In both sources, we observe large changes in the spin-down torque up to a factor of approximately 4, which persist for several months. Using long-baseline phase-connected timing solutions as well as the overall frequency histories, we construct torque noise power spectra for each SGR (Soft Gamma Repeater). The power spectrum of each source is very red (power-law slope is approximately -3.5). The torque noise power levels are consistent with some accreting systems on timescales of approximately 1 yr, yet the full power spectrum is much steeper in frequency than any known accreting source. To the best of our knowledge, torque noise power spectra with a comparably steep frequency dependence have been seen only in young, glitching radio pulsars (e.g., Vela). The observed changes in spin-down rate do not correlate with burst activity; therefore, the physical mechanisms behind each phenomenon are also likely unrelated. Within the context of the magnetar model, seismic activity can not account for both the bursts and the long-term torque changes unless the seismically active regions are decoupled from one another.
Document ID
20030000431
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Woods, Peter M.
(Universities Space Research Association United States)
Kouveliotou, Chryssa
(NASA Marshall Space Flight Center Huntsville, AL United States)
Gogus, Ersin
(National Space Science and Technology Center Huntsville, AL United States)
Finger, Mark H.
(Universities Space Research Association United States)
Swank, Jean
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Markwardt, Craig B.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Hurley, Kevin
(California Univ. Berkeley, CA United States)
vanderKlis, Michiel
(Astronomical Inst. Amsterdam, Netherlands)
Date Acquired
August 21, 2013
Publication Date
September 1, 2002
Publication Information
Publication: Astrophysical Journal
Publisher: American Astronomical Society
Volume: 576
Subject Category
Astrophysics
Funding Number(s)
CONTRACT_GRANT: NAG5-9350
CONTRACT_GRANT: NSF PHY-99-07949
CONTRACT_GRANT: NCC8-200
Distribution Limits
Public
Copyright
Other

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