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IGR J17497-2821: Refined Swift/XRT Analysis

ATel #900; J. A. Kennea (PSU), D. N. Burrows (PSU), J. Nousek (PSU) and N. Gehrels (NASA/GSFC)
on 28 Sep 2006; 16:11 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

Subjects: X-ray, Gamma Ray, Transient

Referred to by ATel #: 906, 907

IGR J17497-2821 (e.g. Soldi et al., ATEL #885) has been observed by the Swift/XRT on 4 occasions from Sept 19th, 2006 to Sept 26th, 2006, since being initially detected by INTEGRAL on Sept 17th, 2006. We report on a refined analysis of these combined data. Swift/XRT positions for this source previously reported have been inconsistent (e.g. Walter et al., ATEL #889, Chaty et al., ATEL #897), this is most likely due to the point source falling on hot columns in the XRT detector, making accurate centroiding of the source difficult. By combining the four observations and correcting for the hot columns, we find a refined XRT position of:

RA(J2000) = 17h 49m 38.1s,
Dec(J2000) = -28d 21m 16.9s,

with an estimated uncertainty of 5.3 arcseconds radius (90% containment). Note that this error circle is 50% larger than calculated with the standard software due to current issues with the XRT boresight (Burrows et al., GCN #5628). This position lies 4 arcseconds from the tentative IR counterpart "candidate 3" reported by Chaty et al. (ATEL #897), and 19 arcseconds from the originally reported Swift/XRT position (Walter et al., ATEL #889). 2MASS 17493780-2821181 lies 4.6 arcseconds from the refined position, the only cataloged source within the 90% XRT error radius.

Although the source does show some variability over the observations in XRT, the source has not visibly faded, showing a mean XRT count rate of ~4 counts/s in Window Timing (WT) mode.  The WT spectra is well fit by an absorbed power-law model, with the following parameters:

N_H = (4.8 +/- 0.3) x 1022 cm-2
Photon Index = 1.6 +/- 0.1
Reduced Chi-squared = 1.2 (147 dof)
Flux = 3.3 x 10-10 erg/s/cm2 (0.3-10.0 keV, uncorrected for absorption).

Assuming a distance of 8.5 kpc for this source, and correcting for absorption, the 0.3-10.0 keV X-ray luminosity of this source is approximately 7 x 1036 erg/s. There is no evidence for any line features in the spectrum.