X-Ray Observations of Type Ia Supernovae with Swift: Evidence of Circumstellar Interaction for SN 2005ke

We present a study of the early (days to weeks) X-ray and UV properties of eight Type Ia supernovae (SNe Ia) that have been extensively observed with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on board Swift, ranging from 5 to 132 days after the outburst. SN 2005ke is tentatively detected (at a 3-3.6 σ 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 [L0.3-2 = (2 ± 1) × 1038 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 ≈ 3 × 10-6 M☉ yr-1 (vw/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 on board Swift, starting around 35 days after the explosion. The nondetection of SN 2005ke with Chandra 105 days after the outburst implies a rate of decline steeper than LX ∝ 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.