We present results on the X-ray and optical/UV emission from the type IIP 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 the Swift observatory .
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 \pm 0.4 ) \times 10 ^ { 39 } ~ { } { 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 \dot { M } \approx 1 \times 10 ^ { -5 } ~ { } M _ { \odot } ~ { } { yr } ^ { -1 } ~ { } ( v _ { w } / 10 ~ { } { % km~ { } s } ^ { -1 } ) is inferred .
The mass-loss rate is consistent with the non-detection in the radio with the VLA on days 2 , 9 , and 11 after the explosion and characteristic of a red supergiant progenitor with a mass around \approx 12 – 15 ~ { } { M _ { \odot } } 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 L _ { x } \propto t ^ { - n } with index n = 1.2 \pm 0.6 is inferred .
Since no other SN has been detected in X-rays prior to the optical peak and since type IIP 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 ( \approx 10 – 100 ) , inconsistent with the ejecta velocity inferred from optical line widths , we conclude that Inverse Compton scatterring is an unlikely explanation for the observed X-ray emission .
The fast evolution of the optical/ultraviolet ( 1900–5500Å ) spectral energy distribution and the spectral changes observed with Swift reveal the onset of metal line-blanketing and cooling of the expanding photosphere during the first few weeks after the outburst .