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INTEGRAL observations of XTE J1818-245

ATel #583; S. E. Shaw (Southampton, UK / ISDC, Geneva); E. Kuulkers (ESA/ESAC, Spain); M. Turler, N. Mowlavi, T. Courvoisier (ISDC, Geneva); C. Markwardt (NASA/GSFC, USA); T. Oosterbroek, A. Orr (ESA/ESTEC, Netherlands); A. Paizis (ISDC, Geneva / IASF, Milano); K. Ebisawa (NASA/GSFC, USA); P. Kretschmar (ESA/ESAC, Spain); R. Wijnands (UvA, Netherlands)
on 17 Aug 2005; 16:02 UT
Credential Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)

Subjects: X-ray, Gamma Ray, Black Hole, Transient

The IBIS/ISGRI instrument aboard INTEGRAL has observed the transient black hole candidate XTE J1818-245 (ATel #578) during seven 1800 second exposures of the Galactic Bulge region between UTC 2005-08-16 23:57 and 2005-08-17 03:39.

The position from the 20-60 keV ISGRI mosaic image is determined as (RA, dec.) = (274.60, -24.53) ± 0.03 degrees. The IBIS/ISGRI position is the same as the ASM position given in ATel #578 and 50 arcseconds from the PCA position quoted in ATel #579.

The source appeared stable over the 7 pointings, with an average flux of 4 cps ( ~ 25 mCrab) and 0.7 cps (~ 17 mCrab) in the 20-60 and 60-150 keV bands, respectively. The source was not in the field of view of the JEM-X instrument during any of the observations.

An average spectrum from 20-100 keV was produced for the source; the spectrum could be fitted with a single power law with photon index = 2.7 ± 0.3, comparable to the value in ATel #579. The integrated 20-40 and 40-80 keV fluxes are 3.0E-10 and 1.8E-10 ergs/cm^2/s, which suggests that the source may have brightened by about a factor of three in 24 hours (ATel #579).

XTE J1818-245 will continue to be observed with INTEGRAL, as part of the Galactic Bulge monitoring programme, approximately every three days for the following 3 months. Quick-look light curves and mosaic images are available to the public from: