The soft X-ray candidate counterpart of IGR J12341-6143

ATel #14039; L. Sidoli (INAF-IASF Milano, Italy), P. Esposito (IUSS Pavia, Italy), V. Sguera (INAF-OAS Bologna, Italy)
on 23 Sep 2020; 12:15 UT
Credential Certification: Lara Sidoli (sidoli@lambrate.inaf.it)

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IGR J12341-6143 is a hard X-ray transient (Bird et al. 2016, ApJS 223, 15), suggested to be a Supergiant Fast X-ray Transient because of its X-ray properties (Sguera et al. 2020, MNRAS 491, 4543).

A series of seven short Swift/XRT observations were performed from September 2019 to June 2020, to refine its sky coordinates. In the combined XRT image (0.3-10 keV; total exposure time of 14 ks) we have detected only one X-ray source compatible with IGR J12341-6143, according to the refined INTEGRAL position reported by Sguera et al. (2020).

The XRT source is at the coordinates R.A. = 12:34:00.22, Dec = -61:43:02.6 (J2000), with an associated error radius of 3.8 arcsec at 90% confidence level (position enhanced by UVOT field astrometry, using the Swift/XRT online tool supplied by the UK Swift Science Data Centre; Evans et al. 2009, MNRAS, 397, 1177). It lies 1.4 arcmin from the INTEGRAL centroid (R.A. = 188.545 deg, Dec = -61.708 deg, J2000; 90% error circle of 3.98 arcmin; Sguera et al. 2020).

The source appears variable (by a factor larger than about 5), being detected only in one of the 7 Swift/XRT observations (ObsID 00011531005, on 58909.66 MJD), with a count rate of 10.78E-03 +/- 3.0E-03 count/s (0.3-10 keV). In the combined XRT image, the source displays an average count rate of 2.47E-03 +/- 0.63E-03 count/s (0.3-10 keV, corrected for PSF, dead time and vignetting).

Using WebPIMMS, with a power law model (photon index = 2) and an absorbing column density of 9E21 cm^-2 (the total Galactic in the source direction; Dickey & Lockman, 1990), the average source intensity translates into an X-ray flux of 2.3E-13 erg/cm^2/s, corrected for the absorption.

Within the XRT error circle, only one optical source is present in the Gaia DR2 database, (6054778507172454912), with an estimated distance of 6.9 (+2.8,-2.0) kpc. This is also a 2MASS near infrared source (12340051-6143034), with the following magnitudes: J = 11.424+/-0.021 mag, H = 10.393+/-0.021 mag, K = 9.819+/-0.019 mag.

The 0.3-10 keV luminosity at the distance of 6.9 kpc is 1.3E33 erg/s, compatible with the quiescence in a SFXT.

This work has been partially supported by the ASI-INAF program I/004/11/4.