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Renewed radio activity in H1743-322 = IGR J1746-3213 = XTE J17464-3213

ATel #314; M. P. Rupen, A. J. Mioduszewski, V. Dhawan (NRAO)
on 6 Aug 2004; 17:14 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Michael P. Rupen (mrupen@nrao.edu)

Subjects: Radio, Infra-Red, Optical, X-ray, Black Hole, Transient

Referred to by ATel #: 575

Very Large Array (VLA) observations of the black hole candidate binary H1743-322 = IGR J1746-3213 = XTE J17464-3213 (e.g., ATEL #301, ATEL #304) show renewed radio activity on 5 August 2004. Two sets of scans, from 01:18 to 01:34 and 03:34 to 03:46 UT, were consistent with a steady flux density of 1.96 +/- 0.15 mJy at 4.86 GHz. Observations on 4 August 2004 from 05:21 to 05:29 UT gave no detection, with a nominal value at the source position of 0.14 +/- 0.17 mJy/beam at the same frequency. Based on past experience with this and other sources, the radio rise probably corresponds to a state change in the accretion disk, most directly reflected in a hardening of the on-going X-ray flare.

During last year's outburst (e.g., ATEL #142) the source remained optically thick in the radio for almost two weeks, then began a series of chaotic radio flares. That slow, inverted-spectrum rise is very unusual among X-ray binaries; assuming the source is currently beginning a similar outburst, multi-wavelength observations would be extremely useful in understanding this phase.

The best radio position for the core is:

17 46 15.5980 +/- 0.0050
-32 14 00.80 +/- 0.18
This is based primarily on data taken during the 2003 optically-thick rise, with the positions of the phase calibrators corrected to those given in the VLBA Calibrator Survey (VCS2 -- Fomalont et al. 2003). This position is consistent with the core detected in November 2003, as well as the current dectection. It represents an improved version of the radio position reported in ATEL #146, and is 0.36 arcsec east of the proposed infrared counterpart (ATEL #146; IAUC 8112 ). While this is nominally several times the expected rms astrometric error, the radio source associated with the 2003 outburst was quite complex, with multiple components present on most days, generally within half an arcsecond of the above core position. These components probably correspond to short-lived ejecta flung out at relativistic speeds from the core. The inverted radio spectrum during the optically-thick rise suggests very strongly that the radio position is indeed that of the core. This makes further infrared observations during the current outburst especially important, since IR variability would provide the most direct confirmation of the association.

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