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

Abstract

We present new optical, UV and X-ray observations of a highly variable dwarf nova(DN) AX J1549.8-5416. 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 the optical (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. We also analyse archival Swift, Chandra and XMM-Newton observations of the source. Our estimated high duty cycle suggests the X-ray luminosity of this source should be larger than 10E32 erg/s in quiescence. We find a roughly anti-correlation between X-ray and UV flux. The X-ray spectra of XMM-Newton and Chandra can be well described either by a single temperature thermal plasma model or by an isobaric cooling flow model when its X-ray flux is high.