Defining frequency axis for periodogram I am trying to simulate example 8.2.2 from Hayes, Statistical Digital Signal Processing and Modelling, on MATLAB. 

Let $x(n)$ be a WSS process consisting of random phase sinusoid in unit variance.
$$ x(n) = A\sin(n\omega_{0} + \phi) + v(n)$$

$A = 5 $, $\omega_{0} = 0.4\pi$, $N = 256$ 

Can anyone help me figure out how to generate the frequency vector such that the peak appears at $0.4\pi$? I am able to achieve the spectrum that is shown in the example, but my x-axis can only be called frequency bin as of now.
As you have taken 1024 point FFT, multiply the x-axis with a factor of 2*pi/1024. 

For now your peak is at sample number 200. 
200*2*pi/1024 approximately equal to 0.4*pi