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Chandra Localization of the Neutron Star X-ray Transient SAX J1753.5-2349

ATEL # 2540; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON), Craig B. Markwardt (NASA/GSFC)
on 7 Apr 2010; 2:38 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Deepto Chakrabarty (

Subjects: X-ray, Neutron Stars, Transients

As part of an ongoing Chandra X-ray Observatory program for the precise localization of X-ray transients in low-mass X-ray binaries, we obtained a short observation of the neutron star transient/X-ray burster SAX J1753.5-2349 during its current outburst (Chenevez et al. 2010, ATEL #2505). Our observation was made on 2010 April 5, 08:18 TT with an exposure time of 1083.6 s. The source was detected with a signal-to-noise ratio of 15.6.

The best-fit X-ray source position is:

RA(J2000) = 17h 53m 31.896s
Dec(J2000) = -23d 49' 14.86"

with an uncertainty radius of 0.6 arcsec (90% confidence). This is consistent with both previously reported position error circles from the Swift X-ray mission, lying 2.7 arcsec from the original Swift position (Degenaar & Wijnands 2008, ATEL #1809, 3.7 arcsec radius) and 1.8 arcsec from the revised Swift position (Starling & Evans 2008, ATEL #1814, 2.3 arcsec radius). Our new Chandra position supports the candidate infrared counterpart recently reported by Torres et al. (2010, ATEL #2526), lying within 0.2 arcsec of its position.

The HRC-S source intensity was 0.33(2) count/s (0.1-10 keV). This instrument does not provide detailed X-ray spectral information. However, assuming the source's previously reported absorbed power-law X-ray spectrum (ATEL #1809) with photon index gamma=2.2 and hydrogen column density N_H=2.1e22 cm^(-2), the HRC-S count rate corresponds to an absorbed (unabsorbed) X-ray flux of 2.9e-11 (1.0e-10) erg/cm^2/s in the 0.2-10 keV band. The observation was taken in HRC-S timing mode. No X-ray pulsations were detected.

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