[vsnet-grb-info 7963] SGR 0418+5729 Fermi/GBM Detection of Pulsations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9506
SUBJECT: SGR 0418+5729 Fermi/GBM Detection of Pulsations
DATE:    09/06/12 15:39:18 GMT
FROM:    Zsolt Bagoly at Eotvos U.  <zsolt.bagoly at elte.hu>

Zsolt Bagoly (Eotvos Univ.), Peter Veres (Eotvos Univ.,  Bolyai 
Univ.), Istvan Horvath (Bolyai Univ.), Lajos Balazs (Konkoly
Observatory) and Attila Meszaros (Charles Univ.) report:

Following the Fermi GBM/Konus/Swift detection of bursts from the 
new SGR 0418+5729 (van der Horst et al. 2009, GCN #9499), and
the RXTE discovery of the of 9.0783 sec period pulsations in the 
2-10 keV band (E.  Gogus et al. 2009, GCN #9502) we analysed the
June 5 20:40:48.88 (trigger 265927250 / 090605862) observation
of the SGR by the Fermi GBM.

Using the GBM gamma data from the 3 triggered NaI detectors and 
the 2 BGOs we have identified 14 short (shorter than 16ms)
pulses, with intensity >4 sigma above the noise.  5 groups were
identified among these pulses (times are relative to the
trigger):

Group 1: 54.976 s, 181.968 s, 245.408 s, 263.776 s
Group 2: 104.960 s, 223.040 s, 232.080 s
Group 3: 131.008 s, 203.616 s, 257.712 s
Group 4: 98.992 s, 135.104 s
Group 5: 69.984 s, 164.368 s

The in-group time differences for Groups 1-4 correspond to 
multiples of the 9.0783 sec pulsation period (with <6% error).
The probability of such random fluctuation is lower than 5e-4. 
Group 5 appears to be noise.

The phase difference relative to the trigger is 0.044 +/- 0.011 
for the Group 1 pulses and 0.564 +/- 0.004 for the Group 2 
pulses, showing almost a symmetrical behaviour.  The Group 3 and
4 phase differences are 0.409 +/- 0.022 and 0.893 +/- 0.011
respectively. This could be the indication of a more complex
high energy pulse morphology similarly to the RXTE observed one
(E. Gogus et al. 2009, GCN #9502) .

This analysis encourages further follow-up observations at high 
energy.