FindFit[sigma,k4+k3/((k2-x)^2+k1^2),{{k1,.02},{k2,1.5},{k3,.1},{k4,7}},{x}]
Plot[Evaluate[k4+k3/((k2-x)^2+k1^2) /. %],{x,1.35,1.6}]
ListPlot[sigma]
Show[%,%%]


FindFit[delta3,ArcTan[(k2-x),k1],{{k1,.02},{k2,1.5}},{x}]
Plot[Evaluate[ArcTan[(k2-x),k1] /. %],{x,1.35,1.6}]
ListPlot[delta3]
Show[%,%%]


