how to generate a simple Gaussian signal with a chirp distortion superimposed

i am trying to generate a simple gaussian signal on which a a chirp distortion has been superimposed, to do that, i use the following code

fs=100; t1 = -5;t2 = 5;t = t1:1/fs:t2; chirp = exp(-i*pi*(t)'.^2); gaussian = exp(-pi*(t)'.^2); y = chirp+gaussian;

but the result is not the one I wanted, the expected magnitude of the signal is just like this:

the simulation signal comes from Fig. 4. (a) of paper

Digital computation of the fractional Fourier transform HM Ozaktas, O Arikan, MA Kutay, IEEE Transactions on signal processing 1996

In that paper it describe the signal like this: exp (-pi(x - 4)^2) + exp(-i*pi*x^2)*rect(x/16)

i could not understand why use rect(x/16) , but really perplexed about it for a long time, would you please give me some suggestions? Thanks.(by the way ,I do not know how to paste the plot here)