Photometric observations of the radio bright B[e]/X-ray binary CI Cam

We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outbu rst quiescent observations reveal the presence of a dusty envelope around t he system. Pronounced short term variability is observed at all wavebands f rom U-K, but no indication of prior flaring of a similar magnitude to the 1 998 April outburst is found in these data. Data obtained during the 1998 April X-ray flare reveal pronounced optical-r adio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical comp onent is likely to result from a combination of free-free/free-bound emissi on, emission line and thermal dust emission, caused by re-radiation of the X-ray flux, while the behaviour of the multiwavelength radio data is consis tent with emission from expanding ejecta emitting via the synchrotron mecha nism. Post-outburst (1998 August-1999 March) U-M broadband photometric observatio ns reveal that while the optical (UBV) Bur remains at pre-outburst quiescen t levels, near IR (JHKLM) fluxes exceed the pre-outburst fluxes by similar to 0.5 magnitudes. Modelling the pre- and post-outburst spectral energy dis tribution of CI Cam reveals that the structure and/or composition of the du sty component of the circumstellar envelope appears to have changed. Due to a lack of information on the precise chemical composition of the dust with in the system several explanations for this behaviour are possible, such as the production of new dust at the inner edge of the envelope, or modificat ion of the composition of the dust due to X-ray irradiation.