SN 2002bu - Another SN 2008s-like transient

Abstract

We observed supernova (SN) 2002bu in the near-IR with the Hubble Space Telescope (HST), the mid-IR with the Spitzer Space Telescope, and in X-rays with Swift 10 years after the explosion. If the faint L⊙H 10 2 L⊙ HST near-IR source at the transient position is the near-IR counterpart of SN 2002bu, then the source has dramatically faded between 2004 and 2012, from L ≃ 106.0 L⊙ to L ≃ 104.5 L⊙. It is still heavily obscured, τV ≃ 5 in graphitic dust models, with almost all the energy radiated in the mid-IR. The radius of the dust emission is increasing as Rt 0.7 ± 0.4 and the optical depth is dropping as τV t -1.3 ± 0.4. The evolution expected for an expanding shell of material, τV t -2, is ruled out at approximately 2σ, while the τV t -0.8 to t -1 optical depth scaling for a shock passing through a pre-existing wind is consistent with the data. If the near-IR source is a chance superposition, the present-day source can be moderately more luminous, significantly more obscured and evolving more slowly. While we failed to detect X-ray emission, the X-ray flux limits are consistent with the present-day emissions being powered by an expanding shock wave. SN 2002bu is clearly a member of the SN 2008S class of transients, but continued monitoring of the evolution of the spectral energy distribution is needed to conclusively determine the nature of the transient. © 2012. The American Astronomical Society. All rights reserved.