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INTEGRAL sees continuing activity from SAX J1747.0-2853, but not from SAX J1750.8-2900

ATel #3172; E. Kuulkers (ESA/ESAC, Spain), J. Chenevez (DTU Space, Denmark), E. Bozzo (ISDC, Switzerland), J. Alfonso-Garzon (LAEX-CAB/INTA-CSIC, Spain), V. Beckmann (APC, France), T. Bird (Southampton, UK), S. Brandt (DTU Space, Denmark), Th. Courvoisier (ISDC, Switzerland), M. Del Santo (INAF/IASF-Roma, Italy), A. Domingo (LAEX-CAB/INTA-CSIC, Spain), K. Ebisawa (ISAS, Japan), P. Jonker (SRON, The Netherlands), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (GSFC, USA), T. Oosterbroek (ESA/ESTEC, The Netherlands), A. Paizis (INAF-IASF, Italy), K. Pottschmidt (UMBC/NASA GSFC, USA), C. Sanchez-Fernandez (ESA/ESAC, Spain), and R. Wijnands (UvA, The Netherlands)
on 17 Feb 2011; 08:57 UT
Credential Certification: Erik Kuulkers (ekuulker@rssd.esa.int)

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

Referred to by ATel #: 3181, 3183, 3930

The INTEGRAL Galactic bulge monitoring program (see ATel #438) observations obtained between 2011 Feb 13 11:30 and 15:11 UT show continuing soft X-ray activity from SAX J1747.0-2853 (ATels #3123, #3163).

The JEM-X instrument detects strong flaring activity between 80 and 700 mCrab (3-25 keV). The average JEM-X spectrum is well described (reduced chi-squared is 1.1 for 11 degrees of freedom) by an absorbed black body plus power law (fixing the interstellar absorption, N_H, to 9e22 cm^-2, Natalucci et al. 2004, A&A 416, 699): kT = 1.6+/-0.1 keV and black-body luminosity of (3.8+/-0.3)e37 erg/s (at a distance of 9 kpc, Natalucci et al. 2000, ApJ, 543, L73), power-law index = 3.0+/-0.1 with power-law normalization of 9+/-2 photons/keV/cm^2/s at 1 keV. The total unabsorbed 3-25 keV flux is 7.4e-9 erg/cm^2/s.

Although at the position of SAX J1747.0-2853 we do not detect any emission with IBIS/ISGRI, the analysis is complicated in this region because of the nearby `blended' source 1E1743.1-2852 (see also ATel #3170). We, therefore, regard the emission seen in this region to be due to SAX J1747.0-2853, as it is the only active source as seen by the Swift/XRT (Atel #3163) and JEM-X. We find a flux of 15+/-2 mCrab, which is consistent with the steep JEM-X spectrum.

SAX J1747.0-2853 is also burst active; we detected a type I X-ray burst starting near UT 13 Feb 13:34 which lasted at least 2 min, and had a net-peak flux of about 700 mCrab (3-25 keV).

The high, soft flux and strong flaring is the first of its kind seen in the Galactic bulge monitoring program, since its start in February 2005 (ATel #438). The behaviour is, however, comparable to that seen in March 2004 with INTEGRAL (ATel #256, see also Tarana et al. 2008, PoS(Integral08)045), when the source was also bright and soft.

We note that SAX J1750.8-2900, reported to be active a few days earlier (ATel #3170), is not seen in our observations, with a 3 sigma upper limit of 11 mCrab in JEMX1 (3-10 keV) and 8 mCrab in ISGRI (20-40 keV).

We thank the ISDC for providing us the results of their quick look analysis, on which this ATel is partly based.

INTEGRAL Galactic Bulge Monitoring Program