Power spectral density of sinusoidal signal in noise
It looks like you are looking at the result of a combination of things. 

First of all let us observe the image and try to understand it. The shredded horizontal line with value $\frac{N_{in}}{2B}$ represents $n(t)$ in the frequency domain and the signal $s(t)$ is represented by the two vertical arrows valued $\frac{A^2}{4R_L}$. Two arrows one in the sinus's frequency value and its mirror in the negative side is a representation of a sinuous wave in the frequency domain. The cosinuous wave will have the a similar representation as the sinuous wave in the frequency domain.I will reffer you to the table here

A BPF is a band pass filter and it is a combination of a low pass filter (will only pass frequencies up to a specified $f_0$ frequency) and a high pass filter (will only pass frequencies up from a specified $f_0$ frequency). In short, a BPF will only pass frequencies from a specific band bounded between some $f_1$ and $f_2$ as in $f_1\leq f\leq f_2$. The BPF is represented as a window in the frequency domain. You can see in your image the window with $B$ width around the sine arrows. This is also the reason the noise $n(t)$ is shredded, The filter is cutting it off outside the window's boundary. In the time domain a BPF will be represented by a $sinc()$ function, as can be seen in the table in this page.

I think your question needs additional data, since it lacks an explanation of what exactly $R_L$ is. I am assuming it is a resistor and this is some sort of an electronic circuit but if you want any further help you need to supply more detailed on the system.