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Swift XRT measure of the SGR 0501+4516 spin period

ATEL # 1682; V. Mangano (INAF-IASF PA), J. Kennea (PSU), M. Perri (ASDC), G. Cusumano (INAF-IASF PA), D. N. Burrows (PSU), N. Gehrels (GSFC), D. Palmer (LANL), S. Barthelmy (GSFC)
on 27 Aug 2008; 17:49 UT
Password Certification: Vanessa Mangano (

Subjects: X-ray, Pulsars, Soft Gamma-ray Repeaters, Transients
Referred to by ATEL #: 1683

Swift XRT observed SGR 0501+4516 from 2008-08-22 12:43:36 s UT to 2008-08-24 01:35:43 s UT in Photon Counting (PC) mode and from 2008-08-26 05:14:58 s UT to 2008-08-27 02:31:59 s UT in Windowed Timing (WT) mode for a total of about 38 ks exposure in PC and 30 ks in WT. We performed the barycentric correction of photon arrival times and a search for coherent pulsations over the full data set in the 0.2-10 keV band with epoch folding search techniques. We had a highly significant detection at the period
P = 5.7620697 +/- 0.0000015 s
The quoted error is at the 90% confidence level and have been calculated following the method described in Cusumano, Massaro & Mineo, 2003, A&A, 402, 647. The reference epoch is at 2008-08-22 12:42:08.278 s (Terrestrial time) corresponding to the beginning of the PC observation. This value is at < 2 sigma from the RXTE measure of 5.769 0.004 s (Gogus et al. 2008, ATEL #1677).
The folded light curve shows a perfectly sinusoidal profile with a pulsed fraction of 17% (calculated as the half the difference between the maximum and minimum count rates).
Further analysis to look for possible period evolution is ongoing.

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R. E. Rutledge , Editor
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