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 ofeight Type Ia supernovae (SNe Ia) which have been extensively observed with theX-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) onboard Swift, rangingfrom 5-132 days after the outburst. SN 2005ke is tentatively detected (at a3-3.6 sigma level of significance) in X-rays based on deep monitoring with theXRT ranging from 8 to 120 days after the outburst. The inferred X-rayluminosity [(2+/-1) x 10^{38} ergs/s; 0.3-2 keV band] is likely caused byinteraction of the SN shock with circumstellar material (CSM), deposited by astellar wind from the progenitor's companion star with a mass-loss rate of ~ 3x 10^{-6} M_sun/yr (v_w/10 km/s). Evidence of CSM interaction in X-rays isindependently confirmed by an excess of UV emission as observed with the UVOTonboard Swift, starting around 35 days after the explosion. The non-detectionof SN 2005ke with Chandra 105 days after the outburst implies a rate of declinesteeper than L_x \propto t^{-0.75}, consistent with the decline expected fromthe interaction of the SN shock with a spherically symmetric CSM (t^{-1}). Noneof the other seven SNe Ia is detected in X-rays or shows a UV excess, whichallows us to put tight constraints on the mass-loss rates of the progenitorsystems.Comment: 12 pages, 3 figures, accpeted for publication in ApJ