To: pramesh@ncra.tifr.res.in
Subject: points for the synopsis 
X-Mailer: VM 6.89 under Emacs 20.5.1
--text follows this line--


Pramesh,

I check at the Univ.  There is a form for synopsis and that needs to
be signed by Sykes.  It has to be sent to him by post.  

I have begun working on the synopsis.  Following are the points and
the flow I am trying to maintain.  Let me know if you have any
suggestions to make.  

I will like to converge on this quickly and submit the synopsis now or
else I will be later hitting deadline that I intend to stick to.

Regards,
sanjay
-------------------------------------------------------

0. Spectra and morphology of Galactic objects are primary signatures
   used to identify Galactic SNRs.

   High resolution required for getting reliable morphology.

   Single dish often used at high frequencies to get resolutions ~ 2
   arcmin.  Such observations suffer from confusion from large scale
   emission and from thermal emission which is significant at >2GHz.

   Sp. index for about 40% of the SNRs in the Galaxy are unreliable.
   Many have observations at freq. > 1 GHz.  The low freq. spectra is
   know for even fewer SNRs.

1. Separation of th. vs. nthermal emission
    
      - sp. index_{th} typically -0.1 for \nu > 1 GHz
        sp. index_{th} typically 2.0  for \nu < 1 GHz

      - sp. index_{nth} for typical shell SNRs (80% of the SNRs) ~
        -0.5. 

      - \nu in the range [150,1400] MHz is ideal for separating th. &
        nth. emission.

2. GP has complex emission field with a mix of th. + nth. emission.
   This requires resolution.

   Interferometers insensitive to very large scale emission - an
   advantage over single dish measurements if the upper limit is not
   too small.

   Disadvantages: (1) side lobes from distant strong source (problems
   with MOST etc.)  (2) upper limit on the sensitive to angular scales
   due to missing zero-spacing.

3. Low freq. spectra

     - reliable shape ==> differentiate between possible particle
                          acc. mechanisms 
     - sp. index maps ==> interaction with the ISM,
                          acc. mechanism,
                          interaction with the PW etc.
     - Low freq. turn-over ==> ELDWIM

4. - GMRT provides high sensitivity + high resolution at low
     frequencies.

     Combination of central sq. and arm antennas provides good UV
     coverage (mitigates the disadvantages (1) to a large extend) as
     well good small spacing coverage (mitigates disadvantage (2) to a
     large extend).  In comparision, VLA requires mutli-config.
     observations typically requiring 0.5-1 year to migitage (1) and
     (2).

     An ideal instrument for multi-frequency study of Gal. SNRs.

   - Typically many other sources in the field of view. 

     New extended source/features + pt. source.

     For catalogues HII regions, shape of the spectra above and below
     allows more accurate determination of EM, and size (given the Te
     from RRL data).

     Using whatever info. at other high freq. from the literature +
     possibly HI absorption, it is possible determine the nature of
     compact sources (HII regions vs. compact SNRs vs. extra-Gal
     sources).

5. This dissertation exploited the imaging capabilities at 327 MHz.
   First step towards a more ambitious multi freq. program for
   Galactic astronomy.

6. Relevant description of the GMRT

7. Required software development 

8. Debugging

9. Development of new techniques

10. Results:

     - Confirmation of candidate SNRs.
      
       Most sensitive, highest resolution images at the lowest
       frequencies for these SNRs.

     - New data on a few known SNRs.

     - Nature of new extended objects in the fields

     - Nature of compact sources in the fields

     - Future work