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Swift XRT Observations of SGR 0418+4729

ATEL # 2121; Ersin Gogus (Sabanci Univ.), Chryssa Kouveliotou (NASA/MSFC), Peter M. Woods (Dynetics), on behalf of a larger collaboration
on 9 Jul 2009; 11:12 UT
Password Certification: Ersin Gogus (

Subjects: X-ray, Neutron Stars, Pulsars, Soft Gamma-ray Repeaters, Transients

We observed the new soft gamma repeater, SGR 0418+4729 with the Swift X-Ray Telescope (XRT) starting at 2009 July 8 20:52:35 in photon counting mode. The total exposure time was 2.95 ks. We detect a significant source in the XRT field of view with a count rate of 0.23 cnts/s. The coordinates of this source is RA = 04h 18m 33.70s, Dec = +57d 32' 23.7" (J2000) with an error circle radius of 3.6". Note that the XRT location is about 3.3' from the BAT location and within the 4' BAT error circle (van der Horst et al. ATel#2077).

We also performed timing analysis on the XRT data of this source and identified the same period discovered with RXTE (Gogus et al. ATel#2076). Thus, we confirm that the XRT and RXTE sources are the same.

Preliminary spectral analysis on the total of about 600 source counts (background subtracted) shows that the spectrum is rather soft and can be described by either an absorbed blackbody (nH=(0.5+/-0.2)x10^22 cm-2, kT=0.80+/-0.05 keV) or an absorbed power law (nH=(1.3+/-0.3)x10^22 cm-2, gamma=2.3+/-0.2). Although the power model provides a slightly better fit to data, it is currently difficult to distinguish the better model due to the low S/N level. Unabsorbed flux (obtained with a power law fit) in the 1-10 keV range is 1.9x10^-11 ergs/cm^2/s.

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