/|            
  V   V   SSSS   OOO   PPPP                         ||            
  V   V  S      O   O  P   P              X\#\/#X#\/||\X/X##X#/X  
  V   V   SSS   O   O  PPPP             \X\#/#X#\/X#||/X#\X#X/    
   V V       S  O   O  P              \X#\/#X#\/X#\X||#\X#/X      
    V    SSSS    OOO   P            \X#\/#X\#/X#\X/X\#X#X/        
                                  \X#\#/X#\/X#\X/X##X#/X          
  ***  N    E    W    S  ***    /X#\/#X#\/X#\X/#X#X/X#            
 

MORE FRINGES

Fringes to HALCA have been found in a second 1.6 GHz Usuda-Kashima-HALCA experiment, conducted on May 13th. In the May 7th experiment (reported in last week's issue), fringes were found on the Usuda-HALCA baseline but, due to strong radio frequency interference (RFI) at Kashima, not on the Kashima-HALCA baseline. In the May 13th experiment, the observing frequency was changed to avoid RFI at Kashima, and fringes were found on all three baselines. This has allowed the closure phase to be obtained -- it is found to be stable and distributed around zero. This is another important step towards full space VLBI observations!

MAY 7 FRINGES REVISITED

The May 7th experiment has been re-correlated a number of times in order to gain a better understanding of the delay and delay rates. (Last week's issue incorrectly implied that the time correction file had been used in correlation: in fact only a constant correction had been applied.) The first correlations found that the time derivative of the delay residual was not equal to the delay rate. Several software corrections changed the delay and delay rate so that their variations were compatible. The remaining variations in rate and delay are thought to be due to errors in the orbital determination.

In the May 7th experiment -- in which the projected baselines were selected to be small -- the baseline length varied from 100 million wavelengths to 20 million wavelengths over the two hour observation. The correlated amplitude over this time varied by less than 10% over this time! The signal to noise ratio given in last week's issue was stated as being for a 200 second coherent integration. As one might expect, a range of integration times had been tried, and the quoted signal to noise was for an integration of 60 seconds, though a similar SNR was obtained for a 200 second integration. With the more recent corrections and re-correlation, the SNR is closer to 20 for a 60 second integration. A preliminary result, obtained after the residual delay rate variation is removed from the residual data, is that the coherence drops to 70% with a 30 minute integration time.

Thanks to the all those who sent congratulatory e-mails in response to last weeks issue, and apologies for not being able to respond individually!

THE SEARCH CONTINUES...

Fringe finding experiments are continuing. After several unsuccessful attempts, the May 22nd run with the VLA and VLBA finally yielded data for fringe- searching at Socorro. An S2 format experiment on May 25th will provide data for the S2 correlator in Penticton.

Details of including the HALCA orbit into the simulation software packages, and news of the revitalized VSOP WWW site will appear in the next issue!

 
            Editors: Phil Edwards and Hirax Hirabayashi