X-ray, UV, and optical observations of supernova 2006bp with Swift:: Detection of early X-ray emission

We present results on the X-ray and optical /UV emission from the Type II-P supernova (SN) 2006bp and the interaction of the SN shock with its environment, obtained with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on board Swift. SN 2006bp is detected in X-rays at a 4.5 sigma level of significance in the merged XRT data from days 1 to 12 after the explosion. If the 0.2-10 keV band X-ray luminosity of L-0.(2-10) (1.8 +/- 0. 4); 1039 ergs s(-1) is caused by interaction of the SN shock with circumstellar material (CSM) deposited by a stellar wind from the progenitor's companion star, a mass-loss rate of. M approximate to (1x10(-5) M-circle dot yr(-1))(v(w)/10 km s(-1)) is inferred. The mass-loss rate is consistent with the nondetection in the radio with the VLA on days 2, 9, and 11 after the explosion and is characteristic of a red supergiant progenitor with a mass of approximate to 12-15 M-circle dot prior to the explosion. The Swift data further show a fading of the X-ray emission starting around day 12 after the explosion. In combination with a follow-up XMM-Newton observation obtained on day 21 after the explosion, an X-ray rate of decline of L-X proportional to t(n) with index n 1.2 +/- 0.6 is inferred. Since no other SN has been detected in X-rays prior to the optical peak, and since Type II-P SNe have an extended plateau'' phase in the optical, we discuss the scenario that the X-rays might be due to inverse Compton scattering of photospheric optical photons off relativistic electrons produced in circumstellar shocks. However, due to the high required value of the Lorentz factor (10-100), which is inconsistent with the ejecta velocity inferred from optical line widths, we conclude that inverse Compton scattering is an unlikely explanation for the observed X-ray emission.