Swift Observations of SGR 0418+4729
ATel #2127; J. R. Cummings (NASA/GSFC/CRESST), K. L. Page (U Leicester), A. P. Beardmore (U Leicester), N. Gehrels (NASA/GSFC) on behalf of the Swift Team
on 13 Jul 2009; 13:31 UT
Credential Certification: Jay R Cummings (firstname.lastname@example.org)
Subjects: X-ray, Soft Gamma-ray Repeater
The SGR 0418+5729 (van der Horst et al., GCN #9499, ATel #2077) recently
came out of Sun constraint for Swift.
A bright, periodic source is found with the XRT. BAT and UVOT do not
detect any concurrent emission at the location of the SGR.
We have analysed 19 ks of Swift-XRT Photon Counting mode data, collected
between 20:52:35 on 2009 July 08 and 07:01:56 on July 10.
Using 13.6 ks of XRT Photon Counting mode data and 15 UVOT images, we
find an astrometrically corrected X-ray position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue,
see Evans et al., http://arxiv.org/abs/0812.3662 for details) of
RA, Dec 64.64172, +57.54013 degrees, which is equivalent to
RA (J2000): 04h 18m 34.01s
Dec (J2000): +57d 32m 24.5s
with an error radius of 1.9 arcsec (90% confidence).
The mean 0.3-10 keV count rate over the time of the observations is
0.294 Â± 0.004 count s-1, corresponding to an observed (unabsorbed) flux
of 1.41x10-11 (1.53x10-11) erg cm-2 s-1 over the same energy band.
There may be a long-term modulation with a period of a day or more;
however, since our data only span 1.5 days, this cannot be well
A spectrum extracted from the entire data set can be best-fitted by an
absorbed power-law, with BB kT = 915 +26/-17 eV and NH = (2.1
+0.3/-0.4)x1021 cm-2. An absorbed power-law is a statistically worse fit
to the data (chi2 is 100 higher for the power-law fit).
The XRT was in Photon-Counting mode, with a 2.5 s timing resolution.
Hence determination of the period of the source is imprecise. We
determine the period to be 9.078 +- 0.002 seconds (90% confidence),
matching the period found for the RXTE source in Gogus et al.
(ATel #2076, and as mentioned in ATel #2121, which used part of the
data reported here). Further Swift observations of the source are
scheduled with the XRT in Window Timing mode in response to a TOO
request by Kouveliotou.
This circular is an official product of the Swift team.