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Chandra Localization of IGR J17445-2447

ATel #10395; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON), Craig B. Markwardt (NASA/GSFC)
on 18 May 2017; 17:41 UT
Credential Certification: Deepto Chakrabarty (deepto@space.mit.edu)

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

Referred to by ATel #: 10402

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/ACIS-S observation of the neutron star and type 1 X-ray burster IGR J17445-2447, following reports of its 2017 April outburst (ATEL #10256, #10265). Our observation was made on 2017 May 8, 21:57 TT (MJD 57881.915), which was 25-27 days after the outburst was initially detected in INTEGRAL (ATEL #10256) and the Swift Bulge Survey (ATEL #10265). The exposure time was 969.7 s, using a (1/8)-subarray of the ACIS S3 chip with 0.4 s readout time.

The X-ray source had returned to quiescence by the time of our observation, yielding only a marginal detection. We observed only 3 counts within the 2.2 arcsec Swift error circle (ATEL #10273), but they all fell within a 0.7 arcsec radius of their mean position. Given the background count rate of 0.02 ct/arcsec^2, the chance probability of this is 4.8E-6, corresponding to an equivalent Gaussian detection significance of 4.6 sigma. The mean event position is

RA(J2000) = 17h 44 30.437s
Dec(J2000) = -27d 46' 00.32"

with an uncertainty radius of 1 arcsec. This lies 1.2 arcsec from the Swift position (ATEL #10273, 2.2 arcsec radius), 0.4 arcsec from the bright suggested IR counterpart 2MASS J17443041-2746004 (ATEL #10273, #10284, #10305), and 3.2 arcsec from the faint suggested IR counterpart UGPS J174430.20-274601.2 (ATEL #10305).

The times of the 3 detected events were spread throughout our observation, indicating persistent emission rather than a thermonuclear X-ray burst. The count rate was 0.003(2) count/s. Assuming the previously reported absorbed power-law X-ray spectrum (ATEL #10272) with photon index gamma=2.2 and absorption column density N_H = 4.9e22 cm^(-2), this corresponds to an absorbed (unabsorbed) X-ray flux of 7e-14 (3e-13) erg/cm^2/s in the 0.2-10 keV band.