Possible Radio Counterpart to XTE J1817-330

ATel #717; M. P. Rupen V. Dhawan, A. J. Mioduszewski (NRAO)
on 1 Feb 2006; 05:54 UT
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Credential Certification: Michael P. Rupen (mrupen@nrao.edu)

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Very Large Array (VLA) observations of the black hole candidate binary XTE J1817-330 (ATel #714) on 31 January 2006 show one radio source within the 30-arcsec RXTE PCA error box, at a J2000 position of:
18h 17m 43.537s -33d 01' 07.8"
As these data were taken shortly after an array reconfiguration, the astrometric uncertainty is dominated by the poorly-known positions of the newly-moved antennas, giving a current uncertainty of a few tenths of an arcsecond. This can be improved once the antenna positions are measured more accurately. The 4.86 and 8.46 GHz data are consistent with an unresolved source, the beam sizes being 1.1 x 0.4 arcsec and 0.6 x 0.2 arcsec respectively (both oriented about 5 degrees west of north).

The flux densities were 2.1 +/- 0.3 mJy at 1.40 GHz; 0.83 +/- 0.12 mJy at 4.86 GHz; and 0.58 +/- 0.11 mJy at 8.46 GHz. The radio spectrum thus goes as frequency to the power -0.73+/-0.13. There is no source in the 1.4 GHz NRAO VLA Sky Survey (NVSS; Condon et al. 1998, AJ 115, 1693): the nominal flux density at the position of the source is 0.7 +/- 0.5 mJy/beam.

Given the rarity of unresolved sources at these frequencies, it seems likely that this is the radio counterpart to XTE J1817-330. However, the evidence for variability so far is marginal (2.4 sigma). If this is indeed the radio counterpart, the steep spectrum suggests we are seeing the decaying tail of an outburst. Further VLA observations are planned.

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