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Swift XRT Observation of the XTE J1747-274 field

ATel #500; J. A. Kennea, D. N. Burrows (PSU), C. Markwardt (UMD/GSFC), N. Gehrels (GSFC)
on 24 May 2005; 22:25 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

Subjects: X-ray, Transient

Referred to by ATel #: 521, 1445, 1459

Starting on May 23rd 2005, 22:09UT the Swift observatary observed a field centered on the RXTE source RXTE J1747-274 (Markwardt et al., ATEL #498). After ground processing we obtained 1261s of Photon Counting mode data from the Swift XRT. From these data we find a bright point source located at:

RA(J2000): 17:47:17.8
Dec(J200): -27:20:39

We estimate an uncertainty of 6 arcseconds radius (90% containment). We note that this source is 66 arcseconds away from the INTEGRAL detected transient IGR J17473-2721 (Grebenev et al., ATEL #467) and 7 arcminutes from the RXTE position. This is the only source detected in the XRT field of view and we conclude that the source detected in this field is in fact IGR J17473-2721.

The spectrum of this source is highly absorbed, and best fit with a power-law spectrum. The best fit parameters are N_H = (5.2 +/- 0.4) x 10^22 cm^-2 with a photon index of 2.12 +/- 0.16 (errors quoted at 90% confidence). The flux from this source in the 0.5-10 keV range is (8.4 +/- 0.9) x 10^-10 erg/s/cm^2. Assuming a distance of 8.5 kpc and correcting for absorption this gives an X-ray luminosity of approximately 2 x 10^37 erg/s (0.5 - 10 keV).

It is noted that this flux is approximately a factor of ten lower than the flux reported from XTE J1747-274 in ATEL #498. Continuing measurements of XTE J1747-274 with RXTE have shown that the source continues to be visible at the flux level seen on May 20th. Therefore we suggest that XTE J1747-274 is in fact outside of the XRT field of view, which is defined as as a box with the corners at the following coordinates:

(1) RA=17:48:21 Dec=-27:21:08
(2) RA=17:46:58 Dec=-27:17:04
(3) RA=17:46:42 Dec=-27:34:49
(4) RA=17:48:06 Dec=-27:38:12