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From: allan@noao.UUCP
Newsgroups: net.astro
Subject: Re: Large sources of short period pulses
Message-ID: <358@noao.UUCP>
Date: Fri, 22-Jun-84 13:55:44 EDT
Article-I.D.: noao.358
Posted: Fri Jun 22 13:55:44 1984
Date-Received: Sat, 23-Jun-84 04:14:45 EDT
References: <68800001@hpfcrx.UUCP>
Organization: Natl. Optical Astronomy Obs.  Tucson AZ USA
Lines: 24

I do not see any objection to your idea IN PRINCIPLE. However, most astronomical
sources of radiation are not lasers and so your idea does not then apply.
We can recognise sources which are lasing (actually they are masers) by
their brightness temperature being too high.

Perhaps it is time to clear up all this discussion about pulsation times.

Fact: There is no way that a source of radiation can vary significantly on
      a time shorter than the light travel time across the source if the 
      source is radiating isotropically.

The conditional clause in the above sentence provides the loop hole.
In cases where the radiation is not isotropic, due to relativistic beaming,
laser action, or anything else, then it is POSSIBLE (but not certain) to get
faster variations. However, most astrophysical sources are sufficiently close
to radiating isotropically that the light travel time argument is a useful
working tool.


Peter (theories to go) Allan
Kitt Peak National Observatory
Tucson, Az
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