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IGR J16558-4150: a new hard X-ray transient detected by INTEGRAL

ATEL # 987; S. Soldi (ISDC, Switzerland), S. Shaw (Southampton, UK), J. Miller (Univ. of Michigan), E. Kuulkers (ESA/ESAC), M.D. Caballero-Garcia (LAEFF/INTA), M. Diaz Trigo (ESA/ESAC), on behalf of a larger collaboration
on 5 Feb 2007; 16:08 UT
Password Certification: Erik Kuulkers (

Subjects: X-ray, Transients

A new hard X-ray transient has been discovered by the imager IBIS/ISGRI on board of INTEGRAL, during the public ToO observation of GX 339-4 conducted between 2007 Jan 30th 15:55 and 2007 Feb 1st 06:11 UTC (ATel #980, #986). The new source, IGR J16558-4150, was detected at the position RA = 253.95 DEC = -41.83, with 3 arcmin accuracy. The source was clearly visible in the 127 ksec mosaic image of the observation, with an average flux of about 8 mCrab and a detection significance of 8.6 sigma, in the 20-40 keV band. In individual 2.6 ksec pointings, the source is not detected, indicating that 20-40 keV flux is not strongly variable. The source is not detected in the mosaic image at higher energies, with an upper limit of 4 mCrab in the 40-80 keV band. IGR J16558-4150 is not detected at lower energies by the JEM-X instrument, with an upper limit of ~15 mCrab in the 3-30 keV range.

Only the IR source IRAS 16520-4146 is reported in Simbad within the ISGRI error circle, at 2.6 arcmin. The closest known X-ray source is XMMU J165520.0-41485, at a distance of 5.3 arcmin from our above quoted position.

This region will be observed again by INTEGRAL in the coming weeks (schedule available here

Follow-up observations of this new transient are strongly encouraged at all wavelengths.

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R. E. Rutledge , Editor
ATEL Mirror v1.0 Updates