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ATEL # 1287; P. Romano (INAF-OABrera), L. Sidoli (INAF-IASF Milano) V. Mangano (INAF-IASF Palermo), S. Mereghetti (INAF/IASF Milano)
on 19 Nov 2007; 14:16 UT
Password Certification: Lara Sidoli (firstname.lastname@example.org)
Subjects: X-ray, Binaries, Neutron Stars, Pulsars
The field of the hard X-ray source XTE J1859+083 was observed with Swift/XRT for 9.7 ks from 2007-11-16 15:08:46 to 2007-11-17 23:33:56 UT. The Swift/XR data show no X-ray sources within the XTE/PCA position error region of 2 arcmin radius centered on R.A. (J2000) = 18h 59m 06s, Dec=+08d 15m 00s (Marshall et al. 1999, IAUC7240).
A 3-sigma upper limit on a source within the Swift/XRT error box can be placed at 5E-14 erg/cm2/s in the energy range 0.3-10 keV (for a powerlaw spectrum with a photon index of 2, no intrinsic absorption and a Galactic absorption of 9E21 cm-2).
XTE J1859+083 was classified as a transient High Mass X-ray Binary based on the detection of pulsed X-ray emission with a period of 9.801 +/- 0.002 s during the discovery observation (PCA/XTE, IAUC7240), when the source flux reached 2E-10 erg/cm2/s (2-10 keV).
The Swift/XRT upper limit demonstrates that the source dynamic range is at least 4000. If the source is a transient Be/XRB, from the pulse period and the position on the Corbet diagram, its orbital period should be roughly of 20-50 days. The high dynamic range could also suggest a Supergiant Fast X-ray Transient nature.
We would like to thank the Swift Team for performing these observations.