TITLE: GCN CIRCULAR NUMBER: 9696 SUBJECT: GRB 090709A: Swift XRT Timing Analysis DATE: 09/07/21 12:18:24 GMT FROM: Nestor Mirabal at U.Complutense de Madrid N. Mirabal (U. Complutense de Madrid) and E. V. Gotthelf (Columbia U.) report: In light of recent reports of quasi-periodic variations in the gamma-ray light curve of GRB 090709A (Markwardt et al., GCN 9645; Golenetskii et al., GCN 9647, Gotz et al., GCN 9649; Ohno et al., GCN 9653), we have analyzed Swift XRT observations of GRB 090709A obtained between 2009 July 9.319 UT and 2009 July 11.862 UT (79s - 61 hr after the trigger assuming T at 2009 July 9, 07:38:34 UT). This period overlaps the BAT light curve from T+79 s to T+150 s (Markward et al., GCN 9645). The first set of observations (390 s) was taken in WT mode (1.77 ms timing resolution), followed by three pointings in PC mode (2.5 s timing resolution). Fast Fourier Transform (FFT) analysis applied to the light curves in each interval shows no significant power down to the Nyquist limit of f < 283 Hz and f < 2 Hz, for the WT and PC mode data, respectively. Furthermore, the power spectrum of the first 120 s of WT mode data (79-469 s after the trigger) does not reveal any significant signal. The FFTs show typical characteristics of both white and red noise during the interval. The absence of oscillations in the X-ray band appears to rule out coherent quasi-periodic variations extending beyond T+150 s. We note that the 8-second cycle derived from the gamma-ray light curve seems at odds with the spin period P ~ 1 ms required to produce an energy release Egamma ~ 10^50 erg from a magnetar engine (Thompson et al. 2004, ApJ, 611, 380), unless the neutron star was born a millisecond pulsar and spun down to a 1-8 s period (depending on the actual GRB redshift) on a ~10 s timescale. The power spectrum of the GRB 090709A light curve (WT mode, 79-469 s after the trigger) can be found at: http://www.gae.ucm.es/~mirabal/grbs/grb090709a/grb090709a_fft.gif