[vsnet-grb-info 6538] SGR 0501+4516: Swift XRT measure of the spin period

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8146
SUBJECT: SGR 0501+4516: Swift XRT measure of the spin period
DATE:    08/08/27 17:53:30 GMT
FROM:    Vanessa Mangano at INAF-IASFPA  <vanessa at ifc.inaf.it>

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)
report on behalf of the Swift Team:

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.