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Chandra Localization of the X-ray Transient XTE J1728-295

ATEL # 2869; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON/CfA/RU), Craig B. Markwardt (NASA/GSFC)
on 24 Sep 2010; 21:06 UT
Password Certification: Deepto Chakrabarty (

Subjects: X-ray, Black Holes, Neutron Stars, Transients
Referred to by ATEL #: 2870, 2991, 2997

As part of an ongoing program for precise localization of X-ray transients in low-mass X-ray binaries, we obtained a short Chandra/HRC-S observation of the suspected black hole transient XTE J1728-295 (=IGR J17285-2922) during its current outburst (ATEL #2823). Our observation was made in timing mode on 2010 September 22, 07:37 TT with an exposure time of 1172 s. The best-fit X-ray source position is:

RA(J2000) = 17h 28m 38.88s
Dec(J2000) = -29d 21' 43.6"

with an uncertainty radius of 0.6 arcsec (90% confidence). This is consistent with the 3.5 arcsec position error circle derived with Swift (ATEL 2824), lying 1.7 arcsec from its center. The HRC-S source intensity was 1.73(4) count/s. Assuming the previously reported absorbed power-law X-ray spectrum (ATEL 2824) with photon index gamma = 2.23 and absorption column N_H = 5.4e21 cm^(-2), this corresponds to an absorbed (unabsorbed) X-ray flux of 5.4e-11 (1.6e-10) erg/cm^2/s in the 0.1-10 keV band. No X-ray pulsations were detected.

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