From: <Chris.Phillips_at_email.protected>
Date: Wed, 31 Aug 2005 12:30:39 +1000 (EST)

Hi Guys,

This message is from Sergei. It bounced for some reason.

Cheers
Chris

-----------------------------------------------

Dear All,

Let me inform you about the progress towards New Zealand radio
astronomy and Trans-Tasman VLBI. The VLBI test was conducted between
Hobart and ATCA last week . This is the second time when the
University of Tasmania generously provides us with the opportunity to
test the whole NZ system at Mt Pleasant Observatory.

In April 2005 the NZ system was tested in Hobart for the first time.
The multibeam correlator was used to cross-correlate between the 14m
and 26m radio telescopes on a short baseline of about 100m. One of the
telescopes (14m) was equipped with the principal components of the NZ
system (feed, L-band receiver, sampler, etc.). We got fringes for a
number of radio sources, including 5Jy QSO. However, the first test
wasn't truly VLBI (just 100m baseline), besides neither clock nor data
recorder were tested properly.

Since April 2005 we (NZ and Australian e-VLBI team) have been trying
to do Trans-Tasman VLBI (very long baseline interferometry). We had
two VLBI sessions between NZ 6m Brent Addis radio telescope (BART-6)
and Australian big radio telescopes in May and July. No fringes were
found. All was checked, double-checked and analyzed, and we came to
the conclusion that the sensitivity of the 6m RT we used in NZ was too
low.

Now Steven Tingay suggested to combine the NZ system with the 14m
antenna again, this time for the VLBI test with Australian Telescope
Compact Array (ATCA). Last week for the second time we brought all our
system from NZ to Tasmania. This time the 14m dish was fully equipped
with the NZ equipment (including the data recorder, Rubidium clock and
even GPS). This time the baseline was very long.

This VLBI test was very successful. A 5 Jy source (0537-441) gave a
very strong fringe (14 sigma with just 1 s integration time). Data was
cross-correlated with the software correlator developed in Swinburne.
The test has proved that the NZ system does work in the conditions of
real VLBI. It is clear now that the 6m RT is marginal in terms of
sensitivity. Now, with much better understanding of the parameters of
the NZ system (such as instrumental time delay, system temperature,
etc.) we are pretty confident that we will get fringes in the next
Trans-Tasman test, provided we use longer integration time. It is also
possible that fringes can be found in the data stored from out
previous VLBI sessions.

Since we started 6 months ago, we learned a lot about the system and
the telescope we use. Some innovative approaches were developed. For
example, it was demonstrated that two inexpensive Rubidium clocks
combined and disciplined with GPS can serve as a reliable VLBI time
standard (dt/t ~ 10E-12). Due to great help and support from our
Australian colleagues and friends we have evolved to the stage when
single-dish radio astronomy became fact in NZ, and Trans-Tasman VLBI
is just the matter of greater collecting area. There is no doubt that
NZ will soon become a part of Australian and international VLBI
network.

We thank John Dickey and Brian Boyle for providing Director's time
and full support in radio observatories of the University of Tasmania
and ATNF. Many thanks to Peter McCulloch and Simon Ellingsen for their
help, as well as to Brett Reid and Eric in the observatory for
round-the-clock support. Massive thankyou to Steven Tingay, the
initiator and the champion of the Trans-Tasman VLBI development. It
was a great pleasure to meet Adam Deller, who turned software
correlation process into art and great fun. We appreciate their help
and hard work. (One of our working days in Hobart lasted 31 hours
non-stop!) Special thanks to Brent Addis, talented New Zealander, who
built fully steerable 6m radio telescope in his backyard, and to Tim
Natusch, brilliant NZ engineer and devoted radio astronomer, for his
great commitment and expertise.

Sergei

P.S. When in Hobart, we tried interferometry for OH maser
330.878-0.367 with strong (S~300 Jy) but narrow (5-7 km/s) emission
line in 1665 MHZ. We could see strong OH line in the spectrum received
on the 14m with NZ system (first NZ radio spectroscopy?).
Surprisingly, we got strong fringe between Hobart and ATCA. Adam
promptly found the explanation: there is a 8 Jy HII region associated
with this maser source.

P.P.S. One of our experiments in Hobart we called "Challenge". We
wanted to find the weakest source observable with 14m+26m
interferometer. It was 1.5 Jy QSO (2322-411), which gave us 5 sigma
fringe with 10 s integration, and 7 sigma fringe with 20 sec
integration time. No fringes were found from 1.0 Jy thermal source
J1514-4748.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

>>>Steven Tingay <stingay_at_astro.<!--nospam-->swin.edu.au> 22/04/2005 8:10:29 p.m.
>>>
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

ystem 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.<!--nospam-->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 2005-08-31 12:31:04