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ABSTRACT  In this paper, we report on radio (Very Large Array and Austrialian Telescope Compact Array) and X‐ray ( RXTE ,  Chandra  and  Swift ) observations of the outburst decay of the transient black hole candidate H 1743‐322 in early 2008. We find that the X‐ray light curve followed an exponential decay, levelling off towards its quiescent level. The exponential decay time‐scale is  ≈ 4 days and the quiescent flux corresponds to a luminosity of erg s −1 . This together with the relation between quiescent X‐ray luminosity and orbital period reported in the literature suggests that H 1743‐322 has an orbital period longer than ≈10 h. Both the radio and X‐ray light curve show evidence for flares. The radio–X‐ray correlation can be well described by a power‐law with index  ≈ 0.18. This is much lower than the index of  ≈ 0.6–0.7 found for the decay of several black hole transients before. The radio spectral index measured during one of the radio flares while the source is in the low–hard state is  −0.5 ± 0.15 , which indicates that the radio emission is optically thin. This is unlike what has been found before in black hole sources in the low–hard state. We attribute the radio flares and the low index for the radio–X‐ray correlation to the presence of shocks downstream the jet flow, triggered by ejection events earlier in the outburst. We find no evidence for a change in X‐ray power‐law spectral index during the decay, although the relatively high extinction of  N H ≈ 2.3 × 10 22  cm −2   limits the detected number of soft photons and thus the accuracy of the spectral fits.

Following the 2008 outburst decay of the black hole candidate H 1743‐322 in X‐ray and radio