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Chandra Localization of IGR J16597-3704

ATel #10898; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON), Craig B. Markwardt (NASA/GSFC)
on 27 Oct 2017; 00:04 UT
Credential Certification: Deepto Chakrabarty (deepto@space.mit.edu)

Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient

As part of an ongoing Chandra X-ray Observatory program for precise localization of X-ray transients in low-mass X-ray binaries, we obtained a short Chandra/HRC-S observation of IGR J16597-3704 in the globular cluster NGC 6256, following reports that it was in outburst on October 21 (ATEL #10880, #10881). Our observation was made in TIMING mode on 2017 October 25, 12:13 TT (MJD 58051.509), which was 4 days after the outburst was first detected by INTEGRAL (ATEL #10880). The exposure livetime was 1162.6 s.

The best-fit X-ray source position is:

R.A. (J2000) = 16h 59m 32.90s
Decl. (J2000) = -37d 07m 14.3s

with an uncertainty radius of 0.6 arcsec (90% confidence). This is consistent with the 3.6 arcsec Swift error circle (ATEL #10881), lying 0.3 arcsec from its center. Our position is also coincident (0.08 arcsec difference) with the recently reported radio counterpart (ATEL #10894).

The source was detected with a mean count rate of 2.33(4) count/s. Assuming the previously reported absorbed power-law X-ray spectrum (ATEL #10881) with Gamma=1.3 and N_H = 1.4e22 cm^(-2), this corresponds to an absorbed (unabsorbed) flux of 2.8e-10 (4.0e-10) erg/cm^2/s in the 0.2-10 keV band. No pulsations were detected.