Number 17
May 2007
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European VLBI Network
Newsletter Number 17 May 2007 |
| EVN Homepage | Publications | Meetings | User Support | Proposals | JIVE Homepage | Newsletter Archive |
Observing proposals are invited for the EVN, a VLBI network of radio telescopes spread throughout Europe and beyond, operated by an international Consortium of institutes.
The EVN is open to all astronomers. Use of the Network by astronomers not specialised in the VLBI technique is encouraged.
The Joint Institute for VLBI in Europe (JIVE) can provide support and advice on project preparation, scheduling, correlation and analysis.
| 2007 Session 2 | May 31 - Jun 20 | 18/21cm, 6cm, 5cm, S/X |
| 2007 Session 3 | Oct 18 - Nov 08 | 18/21cm, 5cm, 7mm, +... |
| 2008 Session 1 | February-March | 18/21cm, 5cm, 1.3cm, +... |
Proposals received by 1 June 2007 will be considered for scheduling in Session 3, 2007 or later. Finalisation of the planned observing wavelengths will depend on proposal pressure. Other wavelengths which may be scheduled in 2007-2008 are 90cm, 50cm, 30cm, and 3.6cm.
To use Northstar, people should register (only for the first proposal submission), enter the information about the investigators and the technical specifications of the proposed observations (equivalent to that previously in the coversheet) using the on-line forms, and upload a scientific justification in pdf or ps format. The scientific justification should be limited to 2 pages in length. Up to 2 additional pages with diagrams may be included. The deadline for submission is 23:59:59 UTC on 1 June 2007.
The detailed Call for Proposals has further information on Global VLBI, EVN+MERLIN and guidelines for proposal submission.
The EVN User Guide describes the network and provides general information on its capabilities.
The EVN Status Table gives current antenna capabilities.
The On-line VLBI
catalogue lists sources observed by the EVN and Global VLBI.
The Chairman of the EVN Consortium, a bottom-up organization, acts as a coordinator, with the aim to pursue the decisions taken by the EVN Executive. To achive results, collaborations of people at the stations and support from the member institutions is essential. The support has been great in the past two years as it usually is. The always present difficulties in finding enough financial support for upgrading and operations of the network, often make the progresses we planned sometime too slow. This is the case for the frequency agility of the telescopes in the array, a project launched long ago with the aim to increase the efficiency of the EVN operations. At present, too few telescopes in the array are flexible in changing the observing frequency in few minutes. On the other hand, the optical fibre link of the telescopes went on much faster than expected. We have now 6 stations able to send data to the EVN JIVE correlator for real-time correlation. Regular tests are organised every six weeks and part of the 24 hours sessions are made available for science observations. The first papers with the results achived by those observations have been already published . Further progress in eVLBI is expected thanks the EC funded project EXPReS. A policy for Target of Opportunity observations is under discussion by the CBD to take advantage of the new possibility offered by real-time correlation, making the EVN more flexible and ready for observations of transient phenomenon.
EVN has succesfully completed the transition from tape drives to Mark5A. The transition phase went on quite smoothly. Now the network is much more reliable and the quality of the data provided to the P.I.s have considerably improved. However, it took more than expected to the stations to achive the needed amount of disks space for recording. The EVN operations can now sustain 10 days of continuous recording at 1 Gbps, greatly increasing the sensitivity of the array. On the other hand the calibration of the array still represents a problem, which mainly derived by the fact that the telescopes in the network are different from each others. There is also a human component which contributes to make the calibration issue critical. In fact, more attention and careful measurements are desired at each station in doing regular check of the telescope performances and in providing the needed calibration information to the PIs. This is an open action item for the network since the beginning.
A period of great changes in the VLBI world is approaching. The data acquisition system, MKIV and VLBA terminals, are becoming obsolete. Plans has been made to face this serious problem. But again, there are difficulties in coordinating the efforts to move faster towards new solutions. New backends have been designed in the recent past based on the huge progresses made by digital technology. EVN has endorsed a project called Digital Base Band Converters. Haystack is developing the so called DBE and NRAO is working, in collaboration with Haystack, on DBEN. What we would like to have are more realiable and cheaper backends which can substitute the analog devices. A Critical Design Review of DBBCs has been recently organized on behalf of the EVN in Bologna (Istituto di Radioastronomia). The Haystack and NRAO experts took part in the discussion as members of the panel. One of the main outcome of the meeting was the desire for stronger collaborations, exchange of expertise and the need to achieve full compatibility between the various designs. New backends are also needed for stations aspiring to join the EVN like Evpatoria (Ukraina) and Irbene (Latvia) and for the coming new stations like Yebes 40m and Sardinia Radio Telescope.
I should have started this contribution writing about the quality of science done with the EVN, or VLBI in general. In my opinion our community is giving a great contribution in astrophysical studies. This was recently made evident by the success of the 8th EVN Symposium held in Torun in terms of participants, mainly young people, number of participants and quality of the contributions. Possibly, the next VLBI symposium in 2008, will be the 1st International VLBI Symposium as a results of a major integration process between the EVN and the VLBA, which started at the EVN CBD meeting held in Bonn. The first outcome of that discussion was an "Addendum to the EVN Memoramdum of Agreement" signed by the EVN Chairman and by the NRAO Director to officially ratify such policy. In the meantime a group of volunteers, supported by young enthusiastic scientists, is elaborating the "EVN2015 Science Vision", a report that will be ready soon for open discussion.
A great future is in our hands.
Franco
Mantovani - IRA-INAF
On 2 February 2007 we carried out the first successful five station e-VLBI observations at 512 Mbit/s. The array consisted of Cambridge, Jodrell Bank (MkII), Medicina, Onsala and a single dish of the Westerbork array. The target source 3C454.3 was observed for about an hour, without notable problems (see image). Torun was also part of the array, but its data rate was limited to about 480 Mbit/ps.
While the dynamic range of this image is limited by the short observation time and the poor uv-coverage, this is an important milestone on the way towards reaching sensitivities comparable to those achieved with traditional disk-based VLBI. During April a major upgrade of the JIVE local network was initiated, as well as software and hardware upgrades of the Mark5As at the telescopes and at JIVE. This resulted in the first sustained 512 Mbit/s data rates from Torun in the beginning of May.
Besides the six telescopes regularly participating in e-VLBI
experiments, additional telescopes will be soon available.
On 5 March 2007 we carried out a fringe test at 22 GHz,
with Metsahovi participating for the first time in real-time
observations with the e-EVN. Fringes were detected to all
participating telescopes: Cm, Jb2, Mc, On60 and Mh. The data rate in
this test was 256 Mbit/s, but earlier formatter tests showed that
reaching 512 Mbit/s from Metsahovi is no problem.
At the end of the year other telescopes are expected to join the e-EVN
array. These are the 100m Effelsberg telescope, the new 40m telescope
at Yebes, and Shanghai. This expansion
will greatly increase the sensitivity, resolution, and image fidelity
of the e-EVN.
In the meantime the EVN Program Committee and the EXPReS e-VLBI Science Advisory Committe have decided on a new e-VLBI observing policy which has been approved by the EVN Directors. The essence of this new policy is that continuum as well as spectral line projects will be supported. It also provides opportunities for triggered projects (only continuum), which will be observed in case a source is found to be in a flaring state before the e-VLBI run. All proposals have to be submitted by the 1st June deadline (see http://www.evlbi.org/evlbi/call_evlbi.html). In case the trigger condition is fulfilled, the EVN PC Chairman has to be notified up to 24 hours before the e-VLBI run. In addition, short observations (less than 2 hours) may be requested from the EVN PC Chairman to check for calibrator or target source compactness, up to three weeks before the run. The coming e-VLBI runs are 25-26 June (for these dates the old policy still holds; see the call for proposals coming out in early June), 21-22 August, 6-7 September, and 9-10 October 2007. We hope that these new rules will open the e-EVN for a much wider range of applications.
Zsolt Paragi, for EXPReS
The code is still under going final verification, but should be merged with the AIPS code shortly, allowing seamless, full polarisation, observations with Yebes as part of the EVN, Pico Veleta as part of the GMVA and Hobart as part of the LBA.
The image of J0743-67 from experiment V182A. The polarisation vectors
are shown overlaid. Absolute polarisation angles can not be derived so
the direction is arbitrary. The core (to the West) is unpolarised (<
1%) and the jet (to the East) is smoothly polarised with a polarised
fraction of approximately 16%.
Richard Dodson, OAN
For more detailed information on the scientific results, please see the astro-ph server: http://arxiv.org/abs/0704.2085
Figure caption: Tentative fits of theoretical models for the
evolution of the source size to the image size of the radio afterglow
of GRB030329. In model 1 there is relativistic lateral spreading
of
the jet, while in model 2 there is no significant lateral expansion
until the jet becomes non-relativistic. The ISM models the external
density is uniform, and the wind model uses a r^-2 profile.
A meeting was held at the headquarters of the National Astronomical Observatory (OAN) of Spain in Madrid, and the Yebes Astronomical Center (CAY) on February 19-20 2007, where representatives of ISAS/JAXA, ESA, NASA, JIVE and OAN attended, focused on the planning of tracking stations for ASTRO-G. The satellite will link to Earth at frequencies around 40 GHz, so a possible tracking station segment would include the 10-m antenna at Usuda (Japan), 20-m at Green Bank (USA), and 14-m at Yebes.
Pictures:
Photo group of the participants in the VSOP-2 tracking-station meeting
at Yebes. The 14-m antenna could be used for tracking, while the new
40-m radiotelescope will participate in the ground network.
Francisco Colomer - OAN
This session followed the very short session 3 of 2006. At the time of scheduling is was forseen that both Urumqi and Shanghai might be unavailable for session 2 (they would be needed for tracking the Chinese Lunar Explorer space mission), thus limiting the capabilities of that session. For this reason session 1 was long, using the entire 3-week reserved period. Arecibo was not available for this session, preventing 1 global project from being scheduled. Before the session the Jodrell Lovell Telescope was found to have a serious crack in one of its wheels and had to be withdrawn from the session. Projects were observed with the Mk2 telescope instead. The Effelsberg telescope was back in operation for the EVN, following the replacement of the sub-reflector and modifications to the prime focus cabin in autumn 2006.
The session contained 1 global project (at 21 cm), and 3 observations using MERLIN. The 1.3cm section contained only a single user observation. This was for a monitoring project requiring an urgent epoch, which could not be observed in session 3 2006 due to the unavailability of Effelsberg and the Chinese antennas. A number of projects were observed using the most sensitive recording mode at 1 Gb/s, including studies of samples of both SDSS quasars and TypeII quasars. At 6cm, the X-ray binary LS 5039 was observed at 3 epochs, with a spacing between epochs of 2 days. At 5cm a 2nd epoch was observed of a 5-epoch project to measure the parallax and proper motion of Galactic methanol masers.
Richard Porcas, EVN Scheduler