XMM-Newton slew-survey counterparts to the INTEGRAL sources IGR J18173-2509 and IGR J16426+6536

ATel #1397; A. Ibarra (ESAC), E. Kuulkers (ESAC), R. Saxton (ESAC)
on 26 Feb 2008; 16:09 UT
Credential Certification: Richard Saxton (richard.saxton@sciops.esa.int)

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We report the first X-ray identification of two INTEGRAL sources which were reported in the 3rd INTEGRAL IBIS/ISGRI soft gamma-ray survey catalog (Bird et al. 2007, ApJS, 170, 175, see also http://isdc.unige.ch/~rodrigue/html/igrsources.html ). They were found through a cross-correlation of the 1st XMM-Newton slew survey catalogue (Saxton et al. 2008, A&A in press) and the INTEGRAL survey catalog.

IGR J18173-2509

Within the INTEGRAL uncertainty (2.2') we find the XMM-Newton slew source XMMLS1 J181722.2-250838. This source was detected during two slews on UT 2003, Sep 23 08:42 and 2004, Sep 25, 10:49, with a statistical significance of 7-sigma and 5-sigma, respectively. The XMM-Newton slew source coordinate are: RA, Dec (J2000.0) = 18h17m22s, -25d08'38" (with a 68% confidence error of 8"), i.e., about 1' from the INTEGRAL position.

The 0.2-12 keV EPIC-pn count rates were 1.19 ± 0.32 and 0.86 ± 0.33, respectively. The corresponding fluxes are 3.8 ± 1.0 and 2.7 ± 1.0 x 10^-12 erg/s/cm² (assuming a spectral model of an absorbed power law with a photon index of 1.7 and an absorption column, N_H = 3x10²⁰ atoms/cm²).

The ROSAT source 1RXS J181723-250831 lies within 0.3' of the XMM-Newton slew source. 1RXS J181723-250831 had a count rate of 0.073+/-0.024 c/s (0.2-2.4 keV), corresponding to an X-ray flux of 2.25 ± 0.75 x 10^-12 erg/s/cm² (0.2-12.0 keV), i.e., consistent with that seen for XMMLS1 J181722.2-250838. We suggest that these two sources are associated with each other.

IGR J16426+6536

Within the INTEGRAL uncertainty of 4.5' we find the 4-sigma significance XMM-Newton slew source XMMLS1 J164303.7+653253 with coordinates RA, Dec (J2000.0) = 16h43m04s, +65d32'53" (with a 68% confidence error of 8"). This is 4.2' from the INTEGRAL position. We estimate that the false detection probability of a random source within a radius of 4.5' is about 0.5%. The source was detected on UT 2003 Dec 19 00:37 with an EPIC-pn count rate of 0.36 ± 0.19 c/s, corresponding to an X-ray flux of 1.1 ± 0.6 x 10^-12 erg/s/cm² (0.2-12 keV).

We note that two ROSAT sources also fall within the INTEGRAL error circle, i.e., 1RXS J164244.8+653628 and 1RXS J164207.3+65384. Based on the position and uncertainties of the XMM-Newton slew source and the two ROSAT sources, we do not regard these X-ray sources to be related to each other; we suggest, however, that one of the three sources may be the INTEGRAL counterpart.

We encourage follow-up at X-ray and other wavelengths to confirm our identification, and association with the INTEGRAL sources.