We present a study of the early ( days to weeks ) X-ray and UV properties of eight Type Ia supernovae ( SNe Ia ) which have been extensively observed with the X-Ray Telescope ( XRT ) and UV/Optical Telescope ( UVOT ) onboard Swift , ranging from 5–132 days after the outburst .
SN 2005ke is tentatively detected ( at a 3–3.6 \sigma level of significance ) in X-rays based on deep monitoring with the XRT ranging from 8 to 120 days after the outburst .
The inferred X-ray luminosity [ L _ { 0.3 - 2 } = ( 2 \pm 1 ) \times 10 ^ { 38 } ~ { } { ergs~ { } s } ^ { -1 } ; 0.3–2 keV band ] is likely caused by interaction of the SN shock with circumstellar material ( CSM ) , deposited by a stellar wind from the progenitor ’ s companion star with a mass-loss rate of \dot { M } \approx 3 \times 10 ^ { -6 } ~ { } M _ { \odot } ~ { } { yr } ^ { -1 } ~ { } ( v _ { w } / 10 ~ { } { % km~ { } s } ^ { -1 } ) .
Evidence of CSM interaction in X-rays is independently confirmed by an excess of UV emission as observed with the UVOT onboard Swift , starting around 35 days after the explosion .
The non-detection of SN 2005ke with Chandra 105 days after the outburst implies a rate of decline steeper than L _ { x } \propto t ^ { -0.75 } , consistent with the decline expected from the interaction of the SN shock with a spherically symmetric CSM ( t ^ { -1 } ) .
None of the other seven SNe Ia is detected in X-rays or shows a UV excess , which allows us to put tight constraints on the mass-loss rates of the progenitor systems .