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Two active X-ray transients in the Galactic Center region as seen by INTEGRAL

ATel #1005; E. Kuulkers (ESA/ESAC, Spain), S. Shaw (Southampton, UK), J. Chenevez, S. Brandt (DNSC, Denmark), T. Courvoisier (ISDC, Switzerland), A. Domingo (LAEFF/INTA, Spain), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (GSFC, USA), N. Mowlavi (ISDC, Switzerland), A. Paizis (INAF-IASF, Italy), D. Risquez (LAEFF/INTA, Spain), C. Sanchez-Fernandez (ESA/ESAC, Spain), R. Wijnands (UvA, The Netherlands)
on 16 Feb 2007; 21:20 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Erik Kuulkers (ekuulker@rssd.esa.int)

Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient, Variables

Referred to by ATel #: 1006, 1008, 1013, 1058, 1185, 1266, 1385, 1513, 1739

The first of a new series of INTEGRAL Galactic bulge monitoring observations (ATel #438, #874) performed between UT 2007, Feb 15 18:35 and 22:17 shows two transient X-ray sources to be active in the Galactic Center region.

One is the recently found source IGR J17453-2853 at RA, Dec (Degrees) = 266.32, -28.89, with a 90% confidence error region of 2 arcmin (Kuulkers et al. 2007, A&A, in press, astro-ph/0701244). The IBIS/ISGRI 20-60 keV flux was about 11 mCrab, with a detection significance of 8. It is not detected in the JEM-X 3-10 and 10-25 keV bands with upper limits of about 5 mCrab in both bands. This source was last seen to be active at similar flux levels between 2005, April 3 and 14. As noted by Kuulkers et al. (2007), if the non-detection with JEM-X is due to absorption in the line of sight, N_H should be larger than about 10^23 atoms per cm^2.

The other source is detected with JEM-X at RA, Dec (Degrees) = 266.40, -29.05, with a 90% confidence error region of 2 arcmin. There are various known X-ray transients within the error circle, such as Swift J174535.5-290135.6 (e.g., ATel #753, #756) or CXOGC J174535.5-290124 (e.g., ATel #753, #892). It is detected at about 22 mCrab in 3-10 keV, with a detection significance of 14. The source is clearly variable on a 15-minute time scale. It is not detected in the JEM-X 10-25 keV band with an upper limit of about 5 mCrab. Follow-up observations with more position sensitive instruments are needed to pin-point the exact origin of the transient X-ray emission.