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Unusually strong X-ray pulsations from Swift J1834.9-0846

ATel #3600; Oleg Kargaltsev (UF), Ersin Gogus (Sabanci Univ. Istanbul), Chryssa Kouveliotou (NASA/MSFC), and George Pavlov (PSU)
on 27 Aug 2011; 18:24 UT
Credential Certification: Oleg Kargaltsev (oyk100@astro.ufl.edu)

Subjects: X-ray, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar

The newest magnetar candidate Swift J1834.9-0846 (D'Elia et al. GCN Circ. #12253, Guiriec et al. #12255) was observed with Chandra/ACIS-S for 13 ks on 2011 August 22, with time resolution of 0.44 s. The timing analysis of the barycentered data reveals an unusually high pulsed fraction at the previously reported frequency of 0.402850 Hz (Gogus et al. ATels #3542, #3576). The pulsed fraction in 2-10 keV for the 733 events extracted from r=1'' circular aperture, centered on the source, exceeds 80%. The RMS measure of pulsation strength exceeds 0.7. The background contribution in the chosen extraction aperture and energy range is essentially zero. The detected pulsations, with a single broad peak per period, are much stronger then those observed from any other magnetar in this energy range. The average source flux during the ACIS observation was 2.4e-12 erg/s/cm2 (absorbed, in 2-9 keV). No noticeable flaring activity was seen during the observation. We have also performed phase-connected timing analysis of the RXTE and Chandra data and produced the following spin ephemeris spanning over a time baseline of ~15 days: nu = 0.40285190(6) Hz and nu-dot = -1.3(1)E-12 Hz/s (Epoch 55783 MJD), consistent with those reported by Kuiper & Hermsen (ATel #3577).