[vsnet-grb-info 9047] Discovery of the Spin Period of SGR 1833-0832

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10535
SUBJECT: Discovery of the Spin Period of SGR 1833-0832
DATE:    10/03/20 16:31:28 GMT
FROM:    Paolo Esposito at INAF-IASF,Milano  <paoloesp at iasf-milano.inaf.it>

Paolo Esposito, Gian Luca Israel, Luigi Stella, Nanda Rea, Andrea Tiengo 
report:

We analysed 22.5 ks of XRT data in Photon Counting (PC) mode of the new 
soft gamma-ray repeater candidate SGR 1833-0832 (Gelbord et al. GCN Circ. 
10526, 10531). The data were barycentered using the X-ray position 
reported in Evans et al. (GCN Circ. 10530). We detect strong pulsations 
from the X-ray source in the 2-10 keV band at 7.5653(5) sec. The 
background subtracted pulsed fraction, defined as the semiamplitude of 
sinusoidal modulation divided by the mean source count rate, is 64+/-4%. 
The pulse is highly significant (the probability of such a signal to 
appear by chance in the search, taking into account the 32768 trials, is 
about 5E-18) and is not present in the background data. We caution however 
that this value is close to three times the XRT PC frame time, 2.507 s. At 
the link below a plot of the source and background data folded at our best 
fit period and at 3*2.507 s can be seen. Further observations are needed 
to confirm this period.

http://www.iasf-milano.inaf.it/~paoloesp/sgr1833.html