<< Graphics`Arrow`
σ = 0.5
g[x_] := 
      (1/(Sqrt[2*Pi]*σ))*
        Exp[((-x^2)/(2*σ^2))]

Plot[g[x], {x, -2, 2}, AxesOrigin -> {-2, 0}, 
        Frame -> True, 
        TextStyle -> {FontSlant -> "Italic", 
            FontSize -> 12, FontWeight -> "Bold"}, 
        FrameLabel -> {"Energia depositata", "dN/dE"}, 
        Prolog -> {Text["E", {0.06,  0.05}, {0, 1}], 
            Text["ΔE", {1.8,  0.7}, {0.5, 0.1}]}, 
        Epilog -> {Line[{{1.5,  0.7}, {0.2, 
                  0.42}}], 
Line[{{-0.59,  
                  g[-0.59]}, {0.59, g[0.59]}}], 
            Line[{{0, g[0]}, {0, 0}}]}];

Plot[g[x], {x, -2, 2}, AxesOrigin -> {-2, 0}, 
        Frame -> True, 
        TextStyle -> {FontSlant -> "Italic", 
            FontSize -> 12, FontWeight -> "Bold"}, 
        FrameLabel -> {"Energia depositata", "dN/dE"}, 
        Prolog -> {Text["E", {0.08,  0.05}, {0, 1}], 
            Text["ΔE", {1.8,  0.7}, {0.5, 0.1}]}, 
        Epilog -> {Line[{{-0.59,  g[-0.59]}, {0.59, g[0.59]}}], 
            Line[{{0, g[0]}, {0, 0}}], 
            Arrow[{1.5,  0.7}, {0.2, 0.42}]}];

h[
        x_] := -2*x - (x - 7)^2*
          Exp[-0.1*(x - 4)]

Plot[h[x], {x, -2, 50}, AxesOrigin -> {-2, 0}, 
        Frame -> True, 
        FrameTicks -> {Automatic, {-100, -50, 0}, None, None}, 
        TextStyle -> {FontSlant -> "Italic", 
            FontSize -> 12, FontWeight -> "Bold"}, 
        FrameLabel -> {"Tempo (ns)", "Segnale"}, 
        Prolog -> {Text["Fronte di salita", {15,  -105}, {0, 
                1}], Text["Discesa", {33,  -40}, {0.5, 0.1}]}, 
        Epilog -> {Arrow[{15,  -100}, {3, -70}], 
            Arrow[{27, -45}, {20, -60}]}];

Plot[-h[x], {x, -2, 60}, AxesOrigin -> {60, 0}, 
        Frame -> True, FrameTicks -> {Automatic, {}, None, None}, 
        TextStyle -> {FontSlant -> "Italic", 
            FontSize -> 12, FontWeight -> "Bold"}, 
        FrameLabel -> {"Tempo (ns)", "Segnale"}, 
        Prolog -> {Text["Tempo di salita", {15,  125}, {0, 1}], 
            Text["Tempo di Discesa", {52,  62}, {0.5, 0.1}]}, 
        Epilog -> {Arrow[{15,  100}, {3, 70}], 
            Arrow[{27, 45}, {20, 60}]}];