IGR J16597-3704 in NGC6256 - Two Possible Counterparts

ATel #10885; Peter Pessev (GRANTECAN, IAC, ULL)
on 23 Oct 2017; 19:53 UT
Credential Certification: Peter Pessev (peter.pessev@gtc.iac.es)

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INTEGRAL discovered a new X-ray transient during the observations of the Galactic Center performed on 2017 October 21. It was designated as IGR J16597-3704 (Bozzo et al. 2107; ATel #10880). Following the discovery, the field was re-observed with Swift on 2017 October 22 for a total exposure time of 1 ks (Bozzo et al. 2107; ATel #10881). A single X-ray source was detected at RA=254.8870 DEC=-37.1207 (J2000), with an associated uncertainty of 3.6 arcsec.

Two GAIA sources are situated within the Swift error circle 5976655143688523136 and 5976655148000703360, with Gaia magnitudes 16.385 and 17.243, situated on 3.315 and 3.395 arcseconds at PA 14.297 and 190.748.

One 2MASS source is located within the error circle 16593293-3707115 with the following magnitudes:

J = 12.9 +/- 0.237
H = 11.929 +/- 0.31
Ks= 10.207 +/- N/A

situated on 3.066 arcseconds at PA 12.603, on a distance 0.267 arcseconds from the brighter Gaia source. Another designation of this source is NOMAD1 0528-0607472. Notably this source appears significantly redder on the Gaia vs. Gaia - 2MASS Ks color magnitude diagram than the locus of the RGB of NGC6256.

There is also a WISE source J165932.58-370714.9 right at the boundary of the Swift error region on 3.58 arcseconds at a PA of 262.696492.

J = 10.184 +/- 0.054
H = 9.169 +/- 0.067
Ks = 8.706 +/- 0.042
W1 = 7.878 +/- 0.026
W2 = 7.744 +/- 0.020
W3 = 7.835 +/- 0.032
W4 = 6.705 +/- 0.075

According to the Schlafly & Finkbeiner 2011 (ApJ 737, 103) and Schlegel et al. 1998 (ApJ 500, 525) extinction maps the visual extinction values are Av = 4.55 and 5.25 magnitudes respectively. (For a two degrees region around the transient position.) Taking into account the extinction values (Aj = 1.234, Ah = 0.785, Ak = 0.529; S&F 2011), according to the Ducati et al. 2001 (ApJ 558, 309) near-infrared color tables, the WISE source is most probably with a red giant (J-Ks)0=0.77. The colors of the first object are consistent with it being an AGB star (J-Ks)0=1.99.

This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration.