NuSTAR timing analysis of Swift J1808.4-1754: the pulse period is ~910 s
ATel #6229; Matteo Bachetti (Univ. de Toulouse and CNRS), John A. Tomsick (SSL/UCB), Karl Foster (Caltech)
on 12 Jun 2014; 17:23 UT
Credential Certification: Matteo Bachetti (matteo.bachetti@irap.omp.eu)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Swift J1808.4-1754 is a transient source, most probably a neutron star binary, first detected on 2014 May 9 (ATEL#6138). An approximately sinusoidal modulation was detected in the Swift/XRT lightcurve, probably due to the neutron star spin, whose period was estimated to be ~924 s (ATEL #6170).
To investigate the nature of this source, a NuSTAR observation was triggered on UT 2014 June 3.378 and lasted until UT 2014 June 4.359, with a livetime of 42.5 ks.
In the NuSTAR data, the pulsation was clearly detected over the whole observation. This allowed a refined timing analysis. We determined the pulse period to be 909.73(11) s. The quoted error is 1-sigma.
The discrepancy between this value and the one determined in ATEL #6170 is mostly due to the non-sinusoidal pulse profile and the sparse sampling of the pulse in the short Swift/XRT observations. We verified that the new solution adapts correctly to the Swift/XRT data used in ATEL #6170.
An article with the detailed description of this timing analysis and the spectral analysis of the NuSTAR data is in preparation.
