High School Determining the transition frequency

[TheCanadian]

I was reading through a paper on MASERs, and perhaps it is obvious, but I am missing how authors determined what type of MASER it is. For example, the observed signal itself has a period of days and the bandwidth is on the order of $10^{-5}$ Hz yet the frequency of the transition responsible for the MASER is 6.7 GHz in methanol. My questions are: how do we know this is the molecule and transition causing this MASER to be seen? Is the bandwidth one computes based on the power spectrum (i.e. FFT of the autocorrelation of the flux density) centred on 6.7 GHz when the researchers are conducting the observations?

My apologies if this is a trivial question, I just seem to be missing something...

 

[DarioC]

https://arxiv.org/abs/astro-ph/0408094
This paper might help.
Thanks for the question--I learned some interesting stuff while looking around on the subject.
DC

 

[DarioC]

https://www.google.com/search?q=6.7...o6U4JrRAhUhwVQKHXRFDksQ_AUIBygC&dpr=1#imgrc=_

Some good spectrum visuals here.
DC