Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site noao.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!princeton!astrovax!noao!allan 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 UUCP: {akgua,allegra,arizona,decvax,hao,ihnp4,lbl-csam,seismo}!noao!allan ARPA: noao!allan@lbl-csam.arpa