Swift/XRT localisation of XTE J1855-026

ATel #1875; P. Romano (INAF-IASF Palermo), S. Mereghetti, L. Sidoli (INAF-IASF Milano), P. A. Evans (UL)
on 15 Dec 2008; 12:20 UT
Credential Certification: Pat Romano (romano@ifc.inaf.it)

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The X-ray source XTE J1855-026 was observed by Swift/XRT on 2008-11-19 from 01:18 to 17:33 UT for a total of 9.5 ks onsource. The source was detected with a count rate of CR=(0.51+/-0.01) counts s^-1. Pulsations at P=359.7+/-0.3 s were clearly detected.

The spectrum (~3100 counts) was fit in the 0.3-10 keV energy range with an absorbed power-law model yielding a photon index of 1.06(-0.15+0.16) and a column density NH=(4.1+/-0.5)E22 cm^-2, in excess of the Galactic one (0.68E22 cm^-2). The observed (unabsorbed) 2-10 keV flux is 7.5E-11 (9.3e-11) ergs cm^-2 s^-1.

The position derived with Swift is RA, Dec(J2000)=283.87685, -2.60516,
which is equivalent to:
RA (J2000): 18h 55m 30.44s
Dec (J2000): -02d 36' 18.6"
with an uncertainty of 1.9 arcsec (radius, 90% confidence).
This position, obtained from the XRT data enhanced by UVOT field astrometry (Goad et al. 2007, A&A, 476, 1401), is 14" from the original ASCA position (12" radius error circle, Corbet & Mukai 2002, ApJ 577, 923) and confirms the identification with the optical counterpart proposed by Verrecchia et al (ATel #102).

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.