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ATEL # 1143; M. Del Santo (INAF/IASF-Roma), P. Romano (INAF/OAB & Univ. Bicocca), L. Sidoli (INAF/IASF-Milano), A. Bazzano (INAF/IASF-Roma)
on 13 Jul 2007; 11:29 UT
Password Certification: Lara Sidoli (firstname.lastname@example.org)
Subjects: X-ray, Neutron Stars
The X-ray source AX J1754.2-2754, reported in the ASCA catalogue (Sakano et al. ApJS, 2002, 138, 19), has been recently unveiled by INTEGRAL as type-I X-ray burster (ATEL #1094). We observed AX J1754.2-2754 with Swift/XRT as 3 ks Target of Opportunity on July 12 2007, 09:12:46 to 14:11:57 UT. The Swift/XRT data reveal only one source within the 50 arcseconds ASCA nominal positional error radius (Sakano et al. ApJS, 2002, 138, 19), for which we obtain the refined position
RA (J2000) = 17h 54m 14.6s
and Dec(J2000) = -27d 54m 34.3s
with an estimated error radius of 3.8 arcseconds (90% confidence). This is 13.2 arcseconds from the ASCA position (Sakano et al. ApJS, 2002, 138, 19).
Preliminary spectral analysis indicates an absorbed power-law with photon index=3.2-0.6+0.7 and Nh=(2.3-0.6+0.7)E22 cm-2. The unabsorbed flux in the 2-10 keV band is 6.3E-12 erg/cm2/s. Assuming a distance of 6.8 kpc (as reported by Chelovekov & Grebenev, ATEL #1094) this translates into a luminosity of 3.4E34 erg/s, which is more than a factor of 2 lower than the one observed in 1999 by ASCA. Further observations are planned.
We would like to thank the Swift Team for making these observations possible, in particular N. Gehrels, the duty scientists as well as the science planners.