Swift/XRT follow-up observations of IGR J17473-2721
ATel #1459; D. Altamirano (UvA), N. Degenaar (UvA), J. in 't Zand (SRON), C. Markwardt (U. Md./CRESST/NASA GSFC), R. Wijnands (UvA)
on 3 Apr 2008; 16:34 UT
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Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient
During an AGILE pointing at the Galactic Center region, a type-I X-ray
burst was detected by SuperAGILE (ATEL #1445) from a position that is
consistent with that of IGR J17473-2721 (ATEL #498 & #500, also known
as XTE J1747-274, ATEL #467) suggesting that this source exhibit
To conclusively identify the burst source with the XTE/IGR transient,
we obtained a Swift/XRT observation of ~ 4.1 ksec on Monday 31st of
March, 2008. Within the SuperAGILE error circle, there is only one
source detected at a position (J2000) of R.A. = 17h47m18.12s, Dec.
=-27:20:38.66, with an uncertainty of ~3.5 arcseconds. This is
consistent with the Chandra position of IGR J17473-2721 (ATEL
#521). Therefore, we confirm that the SuperAGILE X-ray burst has
originated from this source, establishing that this is transiently
accreting neutron star.
The X-ray energy spectrum was extracted from pc-mode data. It can be
fitted with an absorbed power law model with Nh=(3.8+0.48-0.14) x
10^22 cm^-2, photon index 1.68+0.21-0.07 and a final reduced Chi2 of
1.26. The 2-10 keV absorbed and unabsorbed fluxes are 2.27E-10
erg/cm2/s and 3.01E-10 erg/cm2/s, respectively.
We have detected a ~100 seconds long X-ray burst (in one of the
observations recorded in wt -non-imaging- mode). We have extracted the
energy spectrum of the burst peak (first ~2 seconds) and fitted it
with an absorbed black body model. By fixing Nh to the value obtained
above, we find that the temperature is kT~2.29+0.22-0.18 keV, and the
unabsorbed bolometric flux (as estimated in the 0.01-100 keV range)
1.1E-7 erg/cm2/s. We find no evidence for photospheric radius
expansion, implying that the luminosity remained below the Eddington
Limit. From this we infer upper limits to the distance between 3.9 and
5.4 kpc, depending on whether the neutron star photosphere is
hydrogen-rich or poor, respectively (e.g., Kuulkers et al. 2003, A&A,
399, 663). With these upper limits on the distance, we estimate in
1x10^36 erg/s the upper limit of the 2-10 keV Luminosity (persistent emission).
We note that the spectral analysis mentioned above was complicated by
instrumental pile-up issues. We have tried to correct for this by
excluding the inner source pixels from the data-analysis and applying
We thank the Swift team for scheduling the observation.