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ATEL # 1243; A. Tiengo, S. Mereghetti, P. Esposito, A. De Luca (INAF/IASF-Milano), D. Gotz (CEA-Saclay)
on 17 Oct 2007; 13:25 UT
Password Certification: Sandro Mereghetti (email@example.com)
Subjects: X-ray, Gamma-Ray Bursts, Soft Gamma-ray Repeaters
We have analyzed an archival XMM-Newton observation covering the error region of the short soft burst reported by Mereghetti et al. GCN 6927 and possibly associated to the X-ray source AX J1818.8-1559 (Sugizaki et al. 2001, ApJS 134, 77).The observation has been performed on March 28, 2003 and lasted about 8 ks. One source is present within the INTEGRAL error circle at R.A. = 18h18m51.4s Decl. = -15°59'21.1'' (J2000).
The spectrum of this source, obtained with the EPIC pn camera is well fit by an absorbed power law with photon index 1.1 ± 0.3, NH = (3 ± 1) x 1022 cm-2, and absorbed flux 1.4 x 10-12 erg cm-2 s-1 (2-10 keV). The source position and flux are consistent with the values reported for AX J1818.8-1559.
Another X-ray source is present at about 5 arcmin from the center of the INTEGRAL error circle R.A. = 18h19m13.4s Decl. = -16°01'18.8'' (J2000). Its spectrum is well fit by an absorbed power law with photon index 1.0 ± 0.2, NH = (7 ± 2) x 1021 cm-2, and absorbed flux 1.1 x 10-12erg cm-2 s-1 (2-10 keV). The distance of this source from the burst position makes it an unlikely counterpart.
Although both sources have spectra harder than those normally observed in AXPs and SGRs counterparts, it cannot be at the moment excluded that the first source is responsible for the burst. Alternatively, the counterpart of the INTEGRAL burst, had at the time of the XMM-Newton observation a flux smaller than 5 x 10-14 erg cm-2 s-1 (2-10 keV, absorbed, assuming NH = 1022 cm-2 and photon index = 2).