Guobao Zhang, Joseph D. Gelfand, David M. Russell (NYUAD), Fraser Lewis (FT/LJMU), Nicola Masetti (INAF Bologna/Universidad Andres Bello, Santiago, Chile), Federico Bernardini (NYUAD), Ileana Andruchow, L. Zibecchi (Universidad Nacional de La Plata Argentina/Instituto de Astrofısica La PlataArgentina)

We present the results of our analysis of new optical, ultraviolet (UV) and X-ray observations of a highly variable source − AX J1549.8−5416. Both the detection of several fast rise, exponential decay outbursts in the optical light curve and the lack of He II emission lines in the optical spectra suggest AX J1549.8−5416 is a cataclysmic variable of the dwarf nova (DN) type. The multiwavelength analysis of three mini-outbursts and one normal outburst represent one of the most complete multiwavelength studies of a DN and help to refine the relationship between the X-ray, UV and optical emission in this system. 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 is suppressed during the peak of the optical outburst and recovers during the end of the outburst. From our analysis of archival Swift, Chandra and XMM-Newton observations of AX J1549.8−5416, we estimate this DN has a high duty cycle (∼50%), 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 well described by a single temperature thermal plasma model, while at high X-ray fluxes, an isobaric cooling flow model also works. We find that the maximum temperature of the plasma in quiescence is significantly higher than that in outburst.

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