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Chandra detects Swift J174535.5-290135.6 in a relatively bright state

ATEL # 1513; C. O. Heinke (Univ. of Virginia), F. Yusef-Zadeh (Northwestern Univ.), R. Genzel & S. Gillessen (Max-Planck-Institut fur extraterrestrische Physik), K. M. Menten (Max-Planck-Institut fur Radioastronomie), M. Wardle (Macquarie Univ.)
on 8 May 2008; 18:31 UT
Password Certification: Craig Heinke (

Subjects: X-ray, Neutron Stars, Transients

On May 5, 2008, we performed the first, 27.6 ks, Chandra observation of a multiwavelength campaign on Sgr A*. A bright source is detected at a position of R.A.=17h45m35.63s, Decl=-29d01m34.0s (J2000, error of 0.6"). This position is consistent with that of Swift J174535.5-290135.6, detected by Kennea et al. 2006 (ATEL #753), Chenevez et al. 2006 (ATEL #756), Kuulkers et al. 2007 (ATEL #1005), Wijnands et al. 2007 (ATEL #1006), and Porquet et al. 2007 (ATEL #1058), who definitively identified it with AX J1745.6-2901. This source has been intermittently active for 2.2 years (it was fainter than 2e34 ergs/s on Sept. 8, 2006; ATEL #892).

This is the first reported Chandra detection of this source in outburst, allowing a subarcsecond location and confirmation of its quiescent counterpart, CXOGC J174535.6-290133 from Muno et al. (2003, ApJ, 589, 225). Two dips are seen, the first a reduction in flux by 80% for 1500 s. This matches the description of eclipses from AX J1745.6-2901 in Maeda et al. (1996, PASJ, 48, 417). We note that our position is inconsistent with the position of the likely radio counterpart to the Ariel V transient A1742-289 (Davies et al. 1976, Nature 261, 476), confirming Kennea & Skinner's (1996, PASJ, 48, L117) argument that the ASCA and Ariel V sources are distinct.

We have fit the Chandra spectrum (which is significantly piled up) with an absorbed powerlaw, applying the XSPEC pileup model. The best fit gives a photon index of 1.0+0.2-0.3, N_H of 1.7+0.1-0.2e23 cm^-2, and an unabsorbed 2-10 keV flux of 3.7+0.2-0.1e-10 ergs/cm^2/s. For an assumed distance of 8.5 kpc, this gives L_X=3e36 ergs/s. This is the highest flux yet reported from Swift J174535.5-290135.6.

We thank the Chandra X-ray Center for their efforts in scheduling these complex observations.

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