We present the UV , optical , X-ray , and radio properties of the Type IIb SN 2008ax discovered in NGC 4490 . The observations in the UV are one of the earliest of a Type IIb supernova ( SN ) . On approximately day four after the explosion , a dramatic upturn in the u and uvw 1 ( { \lambda _ { c } } = 2600 { ~ { } \AA } ) light curves occurred after an intitial rapid decline which is attributed to adiabatic cooling after the initial shock breakout . This rapid decline and upturn is reminiscent of the Type IIb SN 1993J on day six after the explosion . Optical/near-IR spectra taken around the peak reveal prominent { H \alpha } , HeI , and CaII absorption lines . A fading X-ray source is also located at the position of SN 2008ax , implying an interaction of the SN shock with the surrounding circumstellar material and a mass-loss rate of the progenitor of \dot { M } = ( 9 \pm 3 ) \times 10 ^ { -6 } { ~ { } M _ { \odot } ~ { } yr ^ { -1 } } . The unusual time evolution ( 14 { ~ { } days } ) of the 6 { ~ { } cm } peak radio luminosity provides further evidence that the mass-loss rate is low . Combining the UV , optical , X-ray , and radio data with models of helium exploding stars implies the progenitor of SN 2008ax was an unmixed star in an interacting-binary . Modeling of the SN light curve suggests a kinetic energy ( E _ { k } ) of 0.5 \times 10 ^ { 51 } { ~ { } ergs } , an ejecta mass ( M _ { ej } ) of 2.9 { ~ { } M _ { \odot } } , and a nickel mass ( M _ { Ni } ) of 0.06 { ~ { } M _ { \odot } } .