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Why do high frequency radio observations, particularly of transient phenomenon such as Fast Radio Burst and Pulsars, require increasingly precise localization with increasingly high frequency?

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  • $\begingroup$ Why would you know if the signal was transient if you couldn't aim the antenna back at a particular position? $\endgroup$
    – MaxW
    Jun 25, 2020 at 19:37
  • $\begingroup$ I’m sorry— to clarify, why do higher frequencies require more precise localization (I.e. the higher the frequency the more precise the localization must be). $\endgroup$ Jun 25, 2020 at 19:56
  • $\begingroup$ The word "require" in this question is interesting. Is there a particular reason that you think that high frequency radio observations wouldn't be possible without precise localization? In my experience, the reason that high-frequency radio observations are often accompanied by more precise localization is because it's easier to localize high-frequency radio signals (they don't diffract as much as lower-frequency signals), and localization is itself a desirable quality in an astronomical instrument. $\endgroup$ Jun 25, 2020 at 20:30

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Here is why.

Astronomical objects produce radiation across a broad range of frequencies, depending on which physical mechanisms are in play at any given time. One of the most important tools that astronomers have in doing their work is the ability to look at one object in a range of frequencies- the radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray bands- which furnish clues to what is happening.

To enable this, your radio wave observatory has to be able to precisely locate a sudden blip it detects so that those coordinates can be quickly handed off to the visible light people, so they can point their telescopes right away in the right direction to see that same object before it goes dim again.

To precisely locate a radio object, you need an antenna that can be pointed precisely, which is easier to do with high frequency radio waves than it is with low frequency radio waves. This is because the low frequency waves require gigantic antennas that cannot be swiveled around. The higher the radio frequency, the smaller the antenna needs to be, and the easier it is to aim it.

That said, to pick up weak signals requires a large collecting area or "aperture" which means that even very high frequency radio dishes have to be made as large as possible.

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