Measurement ofBdecays toϕKγ

We search for the decays ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\phi}{K}^{\ensuremath{-}}\ensuremath{\gamma}$ and ${\overline{B}}^{0}\ensuremath{\rightarrow}\ensuremath{\phi}{\overline{K}}^{0}\ensuremath{\gamma}$ in a data sample of $228\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs collected at the $\mathit{\ensuremath{\Upsilon}}(4S)$ resonance with the BABAR detector. We measure the branching fraction $\mathcal{B}({B}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\phi}{K}^{\ensuremath{-}}\ensuremath{\gamma})=(3.5\ifmmode\pm\else\textpm\fi{}0.6\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ and set an upper limit $\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}\ensuremath{\phi}{\overline{K}}^{0}\ensuremath{\gamma})l2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at the 90% confidence level. We also measure the direct $CP$ asymmetry in ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\phi}{K}^{\ensuremath{-}}\ensuremath{\gamma}$, ${\mathcal{A}}_{CP}=(\ensuremath{-}26\ifmmode\pm\else\textpm\fi{}14\ifmmode\pm\else\textpm\fi{}5)%$. The uncertainties are statistical and systematic, respectively.