On the (hard) X-ray activity of SAX J1747.0-2853 as seen with INTEGRAL

ATel #642; E. Kuulkers, P. Kretschmar (ESA/ESAC, Spain), S. Brandt (DNSC, Denmark), R. Wijnands (UvA, Netherlands), T. J.-L. Courvoisier (ISDC, Geneva), K. Ebisawa (NASA/GSFC, USA), J. J.M. in 't Zand (SRON, Netherlands), C. Markwardt (NASA/GSFC, USA), N. Mowlavi (ISDC, Geneva), T. Oosterbroek, A. Orr (ESA/ESTEC, Netherlands), A. Paizis (ISDC, Geneva / IASF, Milano) and S. E. Shaw (Southampton, UK/ ISDC, Geneva)
on 26 Oct 2005; 12:37 UT
Credential Certification: Erik Kuulkers (ekuulker@rssd.esa.int)

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Following the report of the X-ray activity of the neutron star transient SAX J1747.0-2853 (ATels #637, #638, #641) we add that its current outburst was detected by INTEGRAL on Oct 10 and 12, 2005. The JEM-X 3-10 keV fluxes were about 70 and 115 mCrab, respectively, suggesting that the X-ray peak of the outburst was reached near the latter observation. On these two dates the IBIS/ISGRI 20-60 keV flux was 11-12 mCrab. Note that the soft X-ray fluxes are lower than that reached during INTEGRAL observations in a previous outburst (ATel #256). A type I X-ray burst coming from SAX J1747.0-2853 was seen near UT Oct 12 11:05, which lasted for ~20 sec, with a peak flux exceeding 1 Crab (3-10 keV). In the 12 ksec INTEGRAL observation performed on Oct 12 the source was detectable up to around 100 keV. The 3-100 keV X-ray spectrum can be well described by an absorbed (assuming N_H = 7e22 cm^-2) power-law model with photon index 2.5+/-0.15. Comparison of our measurements with those of Chandra (ATels #637, #638) and Swift (Atel #641) indicates that the soft X-ray flux decayed over a week time scale by a factor of 10. During this time the source spectrum seems to have hardened. SAX J1747.0-2853 was not detected in our INTEGRAL Galactic bulge monitoring observations (see ATel #438) between 2005 Feb 18 and Oct 10, and between Oct 12 and Oct 23, with 3-10 keV and 20-60 keV typical upper limits of 15-20 and 8-15 mCrab, respectively. We finally note that SAX J1747.0-2853 is wrongly associated with 1A 1743-288 in Simbad, since the position of SAX J1747.0-2853 (Wijnands et al. 2002, ApJ 579, 422) differs significantly from that of 1A 1743-288 (e.g., Proctor et al. 1978, MNRAS 185, 745).