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Renewed activity of the neutron star X-ray transient SAX J1747.0-2853

ATel #637; Rudy Wijnands, J. Miller-Jones, M. van der Klis (U. Amsterdam), M. Rupen, (NRAO/GSFC), J. in 't Zand (SRON-Utrecht), Q. D. Wang (U. Massachusetts), J. Grindlay, D. Steeghs (CfA), R. Fender, R. Cornelisse, T. Maccarone (U. Southampton), E. Kuulkers (ISOC, ESA/ESAC), C. B. Markwardt (U. Maryland, NASA/GSFC), J. Homan (MIT), E. Cackett (U. St Andrews)
on 20 Oct 2005; 16:45 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Rudy Wijnands (rudy@space.mit.edu)

Subjects: X-ray, Request for Observations, Binary, Neutron Star, Transient

Referred to by ATel #: 638, 641, 642, 892

An X-ray transient was detected in outburst on 18 October 2005 during one of our Chandra/HRC-I observations as part of the XMM-Newton/Chandra monitoring campaign of the 1.7 square degree around Sgr A* (Wijnands et al. 2005, A&A submitted, astro-ph/0508648). The source was located ~15 arcminutes away from the aim-point which did not allow a sub-arcsecond position of the source to be obtained. However, the source position is consistent with that of the neutron-star X-ray transient SAX J1747.0-2853 reported by Wijnands et al. (2002, ApJ, 579, 422; R.A. = 17h47m02.60s, Decl=-28d52m58.9s, 1 sigma error of 0.7"; equinox 2000) and we therefore conclude that the transient can be identified as SAX J1747.0-2853.

No spectral information can be extracted from the HRC-I, so we converted the observed count rate using PIMMS into X-ray fluxes (using an absorbed power-law spectral model with a column density of 7E22 cm^-2 and a photon index of 2). The unabsorbed fluxes were 2.4E-10 erg/cm^2/s and 4.5E-10 erg/cm^2/s in the 2-10 keV and 0.5-10 keV energy range, respectively. For a distance of 8 kpc these fluxes translate into X-ray luminosities of 1.8E36 erg/s and 3.4E36 erg/s, respectively. We note that these fluxes and luminosities are lower limits to the real ones because of vignetting effects which cannot currently be corrected for (see Wijnands et al. 2005 for details). No type-I X-ray bursts were detected.

The source was last reported to be in outburst in March 2004 (ATEL #255, #256). During the June epoch observations of our campaign the source was not detected with an upper limit on its X-ray luminosity of ~1E34 erg/s (2-10 keV; Wijnands et al. 2005). The remaining observations of the other six fields around Sgr A* will be made later today. SAX J1747.0-2853 will be in the field-of-view during one of these observations. We encourage follow-up observations at other wavelengths.