Observation of Two Narrow States Decaying into<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="italic">Ξ</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">c</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow><mml:mi mathvariant="italic">γ</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="italic">Ξ</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">c</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msubsup></mml:mrow><mml:mi mathvariant="italic">γ</mml:mi></mml:math>

We report the first observation of two narrow charmed strange baryons decaying to ${\ensuremath{\Xi}}_{c}^{+}\ensuremath{\gamma}$ and ${\ensuremath{\Xi}}_{c}^{0}\ensuremath{\gamma}$, respectively, using data from the CLEO II detector at the Cornell Electron Storage Ring. We interpret the observed signals as the ${\ensuremath{\Xi}}_{c}^{+\ensuremath{'}}(c{\mathrm{su}})$ and ${\ensuremath{\Xi}}_{c}^{0\ensuremath{'}}(c{\mathrm{sd}})$, the symmetric partners of the well-established antisymmetric ${\ensuremath{\Xi}}_{c}^{+}(c[\mathrm{su}])$ and ${\ensuremath{\Xi}}_{c}^{0}(c[\mathrm{sd}])$. The mass differences $M({\ensuremath{\Xi}}_{c}^{+\ensuremath{'}})\ensuremath{-}M({\ensuremath{\Xi}}_{c}^{+})$ and $M({\ensuremath{\Xi}}_{c}^{0\ensuremath{'}})\ensuremath{-}M({\ensuremath{\Xi}}_{c}^{0})$ have been measured to be $107.8\ifmmode\pm\else\textpm\fi{}1.7\ifmmode\pm\else\textpm\fi{}2.5$ and $107.0\ifmmode\pm\else\textpm\fi{}1.4\ifmmode\pm\else\textpm\fi{}2.5\mathrm{MeV}{/c}^{2}$, respectively.