Probable radio counterpart to IGR J17098-3628

ATel #490; M. P. Rupen (NRAO/GSFC), A. J. Mioduszewski, V. Dhawan (NRAO)
on 12 May 2005; 15:53 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Michael P. Rupen (mrupen@nrao.edu)

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Very Large Array (VLA) observations of IGR J17098-3628 (ATEL #444) were made on March 31st, April 5th, April 12th, and May 4th UT, all at 4.86 GHz. The first data set showed the only significant radio source within the 2 arcminute INTEGRAL error circle, located at (J2000)

17h 09m 45.934s +/- 0.011s -36d 27' 57.30" +/- 0.55" where the error bars are based on uncertainties in a Gaussian fit (and hence reflect only the noise in the image). The data are consistent with a point source, given the 3.9 x 1.2 arcsec (FWHM) resolution (oriented 5 degrees east of north). Comparison of the locations of two background sources detected in each of the four epochs suggests a scatter of at most 0.3 to 0.4 arcseconds from day to day; both those sources are extended, so it is likely that the scatter for the transient would be significantly less than this. The flux density of the radio transient on March 31st was 0.34 +/- 0.07 mJy; for comparison, the lowest negative within the INTEGRAL error circle on this day was -0.30 mJy/beam. The later observations gave nominal flux densities at the radio source position of 0.06 +/- 0.07, 0.16 +/- 0.07, and 0.21 +/- 0.05 mJy/beam; only the last is likely to be a detection. This radio transient lies 0.8 arcseconds from the nominal Swift XRT position (ATEL #476), well within their estimated 5 arcsecond error radius. The radio position is inconsistent with the possible counterparts suggested by Kong (ATEL #477; ATEL #479; see also ATEL #478, ATEL #479). The fading of the radio source from March 31st to April 5th, and its possible re-appearance aound May 4th, are consistent with the X-ray evolution (ATEL #448; ATEL #476). This together with the unlikelihood of a chance superposition within the Swift error circle lead us to conclude that this is indeed the radio counterpart to the X-ray transient.

The NRAO VLA Sky Survey (NVSS; Condon et al. 1998, AJ, 115, 1693) shows no radio source within the Swift error circle, with a nominal flux density at that location of 1.2 +/- 0.6 mJy/beam at 1.4 GHz on 17jan95.

Contour plots of the recent observations are available at

http://www.aoc.nrao.edu/~mrupen/XRT/I1709BB/i1709bb.shtml .

Further VLA observations are planned.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

VLA Observations of IGR J17098-3628