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INTEGRAL discovery of two faint hard X-ray sources in the Galactic Bulge

ATel #790; M. Turler (ISDC, Geneva), S. E. Shaw (Southampton, UK/ ISDC, Geneva), E. Kuulkers (ESA/ESAC, Spain), S. Brandt, (DNSC, Denmark), T. J.-L. Courvoisier (ISDC, Geneva), A. Domingo Garau (LAEFF/INTA, Spain), K. Ebisawa (NASA/GSFC, USA), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (NASA/GSFC, USA), N. Mowlavi (ISDC, Geneva), T. Oosterbroek (ESA/ESTEC, Netherlands), A. Orr (ESA/ESTEC, Netherlands), A. Paizis (IASF, Milano), D. Rísquez Oneca (LAEFF/INTA, Spain), C. Sanchez-Fernandez (ESA/ESAC, Spain), R. Wijnands (UvA, Netherlands)
on 6 Apr 2006; 15:32 UT
Credential Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)

Subjects: X-ray, Transient

Referred to by ATel #: 1799, 1809, 1810

Analysis of INTEGRAL Galactic Bulge monitoring observations (ATel #438) taken between 16:51 and 20:33 UTC on 3 April 2006, reveals the presence of two new sources of hard X-rays. They both have a detection significance exceeding 6 sigma in the IBIS/ISGRI 20-60 keV band with a corresponding flux of ~10 mCrab. The two sources are located close together, approximately 0.8 degrees apart.

Their characteristics are as follows:

  
Name             RA      Dec      Flux        Detsig 


--------------- ------- ------- ---------- ------
IGR J17536-2339 268.409 -23.654 11.0 ± 1.6 6.9
IGR J17541-2252 268.517 -22.871 9.8 ± 1.4 6.5
where RA and Dec are in degrees and flux is in mCrab. The positional uncertainty on both sources is 0.07 degrees (~4'). A search of the Simbad database shows no known X-ray sources within 5 arcmin of either position. However, we note that the X-ray burster SAX J1753.5-2349 is situated approximately 10 arcmin from IGR J17536-2339, and given the positional uncertainty of both the ISGRI and BeppoSAX/WFC locations, we cannot rule out that these sources may be the same.

Unfortunately the new source positions were situated just at the edge of the JEM-X field of view, where the sensitivity of the instrument is low, and hence the detections cannot be confirmed by this instrument.

RXTE PCA observations of the Galactic Center region on 1 April at 04:35 UTC and 4 April at 20:41 UTC place only upper limits on the 2-10 keV emission, of approximately 1 mCrab (systematics dominated). This could indicate that both sources are fast transients, or highly absorbed, if the INTEGRAL detections are confirmed.

More details of the analysis can be found at http://isdc.unige.ch/Science/BULGE

Further observations are encouraged.