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We present the results of our analysis of new optical, ultraviolet (UV) andX-ray observations of a highly variable source $-$ AX J1549.8$-$5416. Both thedetection of several fast rise, exponential decay outbursts in the opticallight curve and the lack of He II emission lines in the optical spectra suggestAX J1549.8$-$5416 is a cataclysmic variable of the dwarf nova (DN) type. Themultiwavelength analysis of three mini-outbursts and one normal outburstrepresent one of the most complete multiwavelength studies of a DN and help torefine the relationship between the X-ray, UV and optical emission in thissystem. We find that the UV emission is delayed with respect to the optical by$1.0-5.4$ days during the rising phase of the outburst. The X-ray emission issuppressed during the peak of the optical outburst and recovers during the endof the outburst. From our analysis of archival Swift, Chandra and XMM-Newtonobservations of AX J1549.8$-$5416, we estimate this DN has a high duty cycle($\sim50\%$), suggesting a quiescent X-ray luminosity larger than $10^{32}$erg/s. We also find the X-ray and UV flux are roughly anti-correlated.Furthermore, we find that, at low X-ray fluxes, the X-ray spectrum is welldescribed by a single temperature thermal plasma model, while at high X-rayfluxes, an isobaric cooling flow model also works. We find that the maximumtemperature of the plasma in quiescence is significantly higher than that inoutburst.

Multiwavelength monitoring of a very active dwarf nova AX J1549.8$-$5416 with an unusually high duty cycle