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Progress toward New Zealand VLBI

From: <stingay_at_email.protected>
Date: Fri, 22 Apr 2005 18:10:29 +1000 (EST)

Dear All,

Sergei Gulyaev and Tim Natusch from the Auckland University of Technology
have been at the Mt Pleasant Observatory of the University of Tasmania for
the last few days, testing their equipment for the upcoming Trans-Tasman
VLBI tests. They have been assisted by Brett Reid, Eric Baynes, Simon
Ellingsen, Guiseppe Cimo, Peter McCulloch, and myself.

I thought that I would bring you up to date with our progress toward the
goal of first Trans-Tasman VLBI, since we have made some very significant
and encouraging first steps.

Sergei and Tim brought with them the equipment they have built:

* 1.6 GHz RF system (feed, LNA, Rubidium, downconversion, receiver);
* sampler and digitiser;
* disk-based recording PC.

We mounted the 1.6 GHz feed on the 14 m antenna at Mt Pleasant and
connected the AUT RF system. We tested coherence of the RF system and
tested the Rubidium clock against the Mt Pleasant maser.

At this point we used the AUT equipment to detect its first astronomical
source, the Crab nebula in Taurus. From this measurement we derived a
system equivalent flux density of approximately 15,000 Jy, allowing us to
calculate the likely system temperature of the AUT system (~300 K). This
is an important number for estimating the baseline sensitivity that we can
expect from our first Trans-Tasman VLBI, and therefore the sources we need
to observe.

We then undertook the first VLBI observation using the AUT equipment,
albeit on quite a short baseline. We ran the 14m antenna using the AUT RF
system and Rubidium clock. We ran the University of Tasmania 26m antenna
(~100m away) using the normal LBA VLBI setup. We used both IF inputs of
the LBA DAS to feed the multi-beam correlator and form the
auto-correlations for the 14m and 26m, as well as the cross-correlation of
the 14m and 26m signals. We found very strong fringes to the Crab nebula
(~few hundred Jy) and strong fringes to 3c161 (~10 Jy) on that 100m
baseline using 5 second integration times. Next, we will test the system
on the weaker sources (~5 Jy) that we will have to use for the first
Trans-Tasman VLBI tests.

We also recorded some data for correlation in software on the Swinburne
supercomputer, for more detailed analysis in the coming weeks.

These tests are highly significant as we have verified the operation of
the AUT equipment, showing that the system sensitivity, time-keeping, and
recording hardware are all up to scratch, giving us a degree of confidence
that the first true VLBI tests, hopefully to be performed in May, will be
successful. We have removed a number of areas of uncertainty in the AUT
system.

I'd like to give a massive thankyou to Eric and Brett in Hobart, as well
as Giuseppe and Simon, and of course Sergei and Tim, for making these
tests successful. We are all very excited about taking the next step on
the way to Trans-Tasman VLBI.

And, congratulations to Tim and Sergei!

Cheers, Steven

##=====================================================##
Dr Steven Tingay stingay_at_astro.swin.edu.au
Swinburne SKA Project Leader
Senior Lecturer

Centre for Astrophysics and Supercomputing
Swinburne University of Technology
Mail No H39
P.O. Box 218, Hawthorn, Vic. 3122, Australia

ph: +61 3 9214 8758
fax: +61 3 9214 8797

http://astronomy.swin.edu.au/ska
##=====================================================##
Received on 2005-04-22 18:11:14