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Swift follow-up observations of EXO 1745-248

ATel #2922; E. Bozzo, C. Ferrigno (ISDC, Switzerland), P. Bordas (ISDC, IAAT)
on 11 Oct 2010; 12:03 UT
Distributed as an Instant Email Notice Transients
Credential Certification: E. Bozzo (enrico.bozzo@unige.ch)

Subjects: X-ray, Gamma Ray, Binary, Neutron Star, Transient

Referred to by ATel #: 2924, 2929, 2932, 2933, 2939, 2940, 2946, 2952, 2958, 2974, 3000, 3044, 3264, 3714, 3892

Following the discovery of a new X-ray outburst from the direction of Terzan 5 with INTEGRAL (most likely due to EXO 1745-248, Atels #2919 and #2920), two Swift/XRT observations were requested. The first pointing (00031841001) was carried out from 2010 October 10 at 17:41:16 to 2010 October 10 at 17:57:52 (UTC, total exposure time 1 ks) in PC mode in order to improve the localization of the source. Only one source is present within the XRT field of view at a position consistent with that reported in Atel #2920. This provide further support in favor of the association between the INTEGRAL source and the X-ray transient EXO 1745-248.

The second Swift pointing (00031841002) was carried out in WT mode from 2010 October 10 at 19:14:57 to 2010 October 10 at 19:48:18 (UTC). The total exposure time was of 2 ks. In the XRT/WT observation the source count-rate was 7.7+/-0.2 (corrected for telescope vignetting and PSF losses) and its spectrum could reasonably well fit (reduced chi^2/dof=1.08/228) with an absorbed blackbody model. We measured an absorption column density of (0.50+/-0.08)E22 cm^(-2), a blackbody temperature of 1.27+/-0.04 keV and a radius of 4.2+/-0.2 Km (for a source distance of 10 kpc). The observed flux was (4.5+/-0.2)E-10 ergs/cm^2/s (1-10 keV, all errors are given at 90% c.l.).

Further observations with Swift have been requested.

We thank the Swift team for their support and the very rapid scheduling of the transient source.