|
European
VLBI Network Newsletter Number
24 October
2009 |
This is the first issue of the EVN Newsletter edited in Torun, Poland.
Magdalena Kunert-Bajraszewska (TCfA) has agreed to become Secretary of the
CBD and naturally the Newsletter Editor for next two years. During this
period the newsletter will continue to be published prior to each VLBI
proposal deadline with the aim on (i) informing astronomers interested in
VLBI about the current capabilities of the EVN array, (ii) bringing EVN
users up to date with recent and planned enhancements, and (iii) underlining
the excellent scientific results being obtained with VLBI technology. All
EVN users are encouraged to communicate their recent scientific results to
Magda (magda@astro.uni.torun.pl) making her work easier and the publication
more interesting.
The EVN Board of Directors will meet at Manchester in November 11-12. We all
look forward to a friendly and constructive meeting, as it is usually for
the group. At the meeting, in addition to discussion about the policy,
operations, and technical developments of the array, we plan to sign the
updated version of EVN Memorandum of Agreement and further review with our
colleagues from Latvia and Ukraine possible ways to join EVN membership.
The new members and new telescopes coming into operation will strengthen EVN
power as the world leading high sensitivity, high resolution radio astronomy
infrastructure on the Northern Hemisphere.
After two years (2007-2009) of serving the EVN community by Prof. Rafael
Bachiller the Chairman of the Consortium Board of Directors I am very
pleased to thank him for the excellent work, which he has done for the
Network expansion and its successful operation.
Personally also I would like to thank him for the support and encouragement
given to me before I succeed as new Chairman of the CBD.
The EVN Consortium Board of Directors approved me as new Chairman of the CBD
in May 2009 at the Onsala Meeting till May 2011. Prof. Simon Garrington
(JBO) has kindly agreed to continue as Vice-Chairman for the same period. I
have been on the Board from 1991 representing Torun Radio Astronomy
Observatory and from 2001 the Torun Centre for Astronomy. I have been
involved into VLBI since 1979 and together with Torun Team joined EVN and
Global Network observations from 1982. The new 32m antenna commissioned in
1994 entered the Network two years later. Torun with modern design telescope
and reliable instrumentation has become an important element of e-EVN and a
valuable addition to W-E baselines, the milestone on connections to Russia
and China. During my directorship at Torun the Centre for Astronomy we
established Torun position as a reliable, robust partner of the EVN. Current
progress on instrumentation, which includes a plan to build a large diameter
dish, should further enforce scientific and technical capabilities of
Torun. The major strategic direction is the EVN expansion towards broad band
- high sensitivity, real time, frequency agility, and extremely high
angular resolution world leading instrument. The enhancement of existing and
development of new generation
correlator for JIVE and the ultra fast fibre-optical links to all network
telescopes are the worth effort activities.
The current capabilities of EVN in terms of sensitivity, frequency coverage
and spectral resolution, wide-field mapping, and rapid-response have allowed
European radio astronomers to produce significant advances in many areas of
modern astronomy.
Adding new European telescopes and those in Russia, China, Ukraine and
Latvia would guide the EVN towards unique future high angular resolution
Northern Array scientifically competitive to the SKA. The EVN is in fact the
SKA path finder and the major drive in technology area, so important and
vital for new generation instruments. FP7 RadioNet EC program coordinates
and shares results of this development and leads the European Radio
Astronomy along the European road map strategy. The EVN will remain for
next decade the major radio astronomy facility in the world around which the
new ideas will continue to emerge.
Very impressive and politically important contributions from EVN to
enlighten the inauguration of IYoA and other international, relevant
activities, have been of great success. It is the time to congratulate all
being involved and to wish more spectacular events, which so well promote
world class research conducted under exceptionally effective and profitable
international co-operation scheme of the VLBI.
Andrzej Kus, Chairman of the EVN Board of Directors.
(This text is also
available on the web at http://www.ira.inaf.it/evn_doc/call.txt)
Observing proposals are
invited for the EVN, a VLBI network of radio telescopes spread throughout
The
observations may be conducted with disk recording (standard EVN) or in real-time
(e-VLBI).
The
EVN is open to all astronomers. Use of the Network by astronomers not
specialized 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. See EVN User Support
at http://www.jive.nl.
2010 Session 1 |
Mar 4 - Mar 25 |
18/21cm, 6cm, 5cm, 30cm |
2010 Session 2 |
May 27 - Jun 17 |
18/21cm, 6cm, 5cm, ...
|
Proposals received by 1 October 2009 will be considered for scheduling
in Session 1, 2010 or later. Finalisation of the planned observing
wavelengths will depend on proposal pressure. Note the possible
availability of 30cm observing in Session 1, 2010.
2009 Dec 10 - Dec 11 (start at 13
UTC) 2010 Jan 27 - Jan 28 (start at 13
UTC) 2010 Feb 10 - Feb 11 (start at 13
UTC) 2010 Mar 30 - Mar 31 (start at 13
UTC) 2010 Apr 22 - Apr 23 (start at 13
UTC) 2010 May 18 - May 19 (start at 13
UTC) |
18/21cm, 6cm, 5cm,
1.3cm 18/21cm, 6cm, 5cm,
1.3cm 18/21cm, 6cm, 5cm,
1.3cm 18/21cm, 6cm, 5cm,
1.3cm 18/21cm, 6cm, 5cm,
1.3cm 18/21cm, 6cm, 5cm,
1.3cm |
Please consult the e-EVN web page at
http://www.evlbi.org/evlbi/e-vlbi_status.html
to check for any updates and for the available array.
Note
that only one wavelength will be run in each session, depending on proposal
priorities.
There
are three e-VLBI observation classes: general e-VLBI proposals; triggered e-VLBI
proposals; short observations. General and triggered e-VLBI proposals must be
submitted by the October 1st deadline to be considered for scheduling in the above
e-VLBI sessions starting from December 2009.
Requests for short
observations (up to two hours) may be submitted up to three weeks prior to any
e-VLBI session.
Continuum and spectral
line observations can be carried out.
See
http://www.ira.inaf.it/evn_doc/guidelines.html for details
concerning the e-VLBI observation classes and the observing
modes.
MERLIN is normally
available for joint EVN+MERLIN observations in all standard sessions, for
any EVN wavelengths which MERLIN supports (18/21cm, 6/5cm,
1.3cm). However, due to the e-MERLIN construction only an incomplete
MERLIN array will be available in early 2010 due to limited resources. For
updated information please consult the web at http://www.merlin.ac.uk/evn+merlin.html
Large
EVN projects
Most
proposals request 12-48hrs observing time. The EVN Program Committee (PC) also
encourages larger projects (>48 hrs); these will be subject to more detailed
scrutiny, and the EVN PC may, in some cases, attach conditions on the release of
the data.
All
EVN, Global and e-VLBI proposals (except ToO
proposals) must be submitted using the on-line proposal
submission tool Northstar. Global proposals will
be forwarded to NRAO automatically and do not need to be submitted to NRAO
separately.
To
use Northstar, people should register (at http://proposal.jive.nl, 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 MUST 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 October 2009.
Further information on
Global VLBI, EVN+MERLIN and e-VLBI observations, and guidelines for proposal
submission are available at:
http://www.ira.inaf.it/evn_doc/guidelines.html
The
EVN User Guide (http://www.evlbi.org/user_guide/user_guide.html) describes
the network and provides general information on its
capabilities.
The
current antenna capabilities can be found in the status tables. For the standard
EVN see http://www.evlbi.org/user_guide/EVNstatus.txt. For the
e-VLBI array see http://www.evlbi.org/evlbi/e-vlbi_status.html
The
On-line VLBI catalogue (http://db.ira.inaf.it/evn/) lists
sources observed by the EVN and Global VLBI.
Tiziana Venturi - Chairperson of the EVN Program
Committee
The magnetic field likely plays a crucial role during the formation of low-mass stars,
in particular in halting the collapse of the parent molecular cloud, transferring angular
momentum and powering the outflows. However, its role during the formation of high-mass
stars is still heavily debated. In particular, it is unclear how the magnetic field influence
the formation and dynamic of disks and outflows. The best probes of the magnetic field at
the smallest scales in the high-mass star-forming environment are maser sources. Their bright
and narrow spectral line emission is ideal for detecting the Zeeman-splitting and weak linear
polarization. Although 6.7GHz methanol masers are the most abundant of the massive star-forming
maser species, the first high resolution methanol maser observations
in full polarization with the EVN were made by us only very recently.
In our successful pilot observations, towards the massive star-forming region W75N, we detected
fractional linear polarization (1-5%) in 8 of the 10 methanol maser features (the residual
polarization leakage after calibration was much less than 1%) revealing a tightly ordered magnetic
field over more than 2000 AU around the radio source VLA 1 and almost perfectly aligned with the
large-scale molecular bipolar outflow (Fig.1). The linear polarization further indicates that the
field is close to the plane of the sky at an angle of about 70 degrees from the line of sight.
We also detected the 6.7GHz methanol maser Zeeman-splitting in 3 maser features (B|| is about 15 mG)
indicating a total magnetic field of the order of 50mG. These important first EVN results have
shown that the linear polarization observation at high angular resolution can reveal the 3D magnetic
field morphology and consequently, with the measured Zeeman-splitting, give the total magnetic field
strength.
This work is available at http://arxiv.org/abs/0908.3585
http://arxiv.org/abs/0908.3585
and it will be published in a forthcoming A&A paper.
Authors:
Gabriele Surcis (AIfA Bonn & MPIfR), Wouter H.T. Vlemmings (AIfA Bonn),
Richard Dodson (ICRAR), and Huib van Langevelde (JIVE & Sterrewacht Leiden)
Fig.1: Positions of methanol (red circles) and water (blue triangles) masers superimposed on 1.3cm continuum contour map of the VLA 1 thermal jet and VLA 2 (Torrelles et al., 1997, ApJ, 489, 744). The red segments indicate the methanol masers linear polarization vectors (40mas correspond to a linear polarization fraction of 1%). The two arrows indicate the direction of the bipolar outflow (66d) and the parallel dashed lines the magnetic field lines (73d +/- 10d) as derived from the linear polarization. |
Recently Ryan et al. (2008, ApJ 688, 43) found and optical arc which looks
like a gravitationally lensed image of a galaxy. However, the foreground
lensing object apparently needed for producing such an arc is not seen in
the deep optical and infrared images. The high mass-to-light ratio implied
by the non-detection would further imply that the total mass of this galaxy
(about 1012.5 solar mass derived from lens modelling) is primarily
in the form of dark matter. As such, this could be the first known example of
a "dark lens"; alternatively, and perhaps less exotically, the lens could be
an unusually obscured galaxy. The only definite information we knew about the
suspected lens is that there is a radio source (J1218+2953) consistent with its
presumed position about 4" away from the optical arc. Its integrated flux density
is 33.9 mJy at 1.4 GHz, according to the VLA FIRST survey. The radio spectrum of
the source is steep, with a spectral index of -0.7.
On 12 November 2008, we applied for short 2-hour e-EVN observations at 1.6 GHz
to check whether there is compact radio emission in the source, which would
indicate an active nucleus in the lensing galaxy. We indeed detected the souce
on 23 January 2009. It was resolved into two components separated by about 0.5".
This result was not easy to interpret so we proposed full-track e-EVN observations
at both 1.6 and 5 GHz at the 1 February 2009 deadline. The speed of this follow-up
was possible only because of the rapid access to the correlated data afforded by
the original short e-EVN observations. The full-track, phase-reference e-EVN
observations of J1218+2953 took place on 24 March 2009 (5 GHz) and on 21 April
2009 (1.6 GHz), both lasting 8 hours. At the lower frequency, our tapered image
reveals a rich and complex structure in a nearly symmetrical "inverted S" shape,
spanning almost 0.7". Were the two "arms" visible in the tapered L-band map both
gravitationally lensed images of the same background source as are the optical arc,
then the lensing should produce flux-density ratios between the inner/outer
components roughly similar in each arm. The map is not consistent with this
interpretation. The source appears unresolved with the Westerbork synthesis array,
whose data were recorded during its participation in the e-EVN observations. This
allowed us to compare the total flux density with the correlated VLBI flux density.
These values were close enough to exclude the possibility that the optical arc
is sufficiently strong in the radio. Therefore both the arc and the radio source
J1218+2953 cannot be gravitationaly lensed images of the same background object.
The observed radio structure may rather reside within a host galaxy providing
the lensing potential to form the optical arc. Although the redshift of the
optically unidentified source is not known, the corresponding projected linear
size could be up to 5-6 kpc for a redshift range of ~0.8-1.5. The two brightest
components are also seen in the 5-GHz image. A weak, relatively flat-spectrum
feature seems to lie in between these two, which might mark the center of this
galaxy. We believe that J1218+2953 is a young, recently triggered and heavily
obscured AGN. It grows in a dense interstellar medium which might cause the
observed two-sided bent radio jet structure. This makes the "dark lens"
interpretation unlikely.
More details on the observations of this interesting object will be published
soon, first in the proceedings of the 8th International e-VLBI Workshop,
EXPReS09, held in Madrid this June.
Authors:
S. Frey (FOMI SGO), Z. Paragi, B. Campbell (JIVE), A. Moor (Konkoly Obs.)
Caption: The naturally weighted 1.6-GHz e-EVN mage of J1218+2953. A Gaussian taper was applied (with half amplitude at 10 Mlambda) to reduce the relative weight of the longest baselines (European antennas to Arecibo), to map the more extended emission. |
Caption: The naturally weighted 5-GHz e-EVN image. |
We have studied the properties of the HI in the radio galaxy NGC 315. Two
HI absorption components are present, a broad one (FWZI ~150 km
s-1 )
redshifted (~80 km s-1 ) with respect to the systemic velocity, and a very
narrow component ( FWZI ~8 km s-1 ). Both are detected and spatially
resolved by the global VLBI observations and, interestingly, the two
absorption components have very different properties, suggesting
that they have very distinct origins.
The broad absorption shows a strong gradient in column density (or spin
temperature) along the jet, with the highest densities (or lowest spin
temperatures) furthest away from the AGN. It also shows a strong velocity
gradient (more than 100 km s-1 over 10 pc) with the more redshifted
velocities away from the AGN. These properties suggest that the gas
producing the absorption is physically close to the AGN. The redshifted
velocities argue against the gas being entrained by the radio jet (and
partly responsible of the deceleration of the jet). Gas located in a thick
circum-nuclear toroidal structure, with orientation similar to the dusty,
circumnuclear disk observed with HST, cannot be completely ruled out
although it appears difficult to reconcile with the observed morphology of the
absorption and it would require inward streaming motion in addition to
rotation. The scenario we favour, is that the gas producing the broad
absorption could be (directly or indirectly) connected with the fuelling of
the AGN, i.e. gas that is falling into the nucleus. If this is the case, the
accretion rate derived is similar to that found for other X-ray luminous
elliptical galaxies, although lower than that derived from the radio core
luminosity for NGC 315. On the other hand, the properties of the narrow
absorption are very uniform. Moreover, it tightly connects, in space and in
velocity, with the H i emission in NGC 315 we detected a few kpc SW of the
nucleus. Most likely, the narrow absorption cloud is quite far from the AGN
and is likely due to material falling into NGC 315. Five nearby, small
gas-rich companions are also detected in H i. This implies that the
environment of NGC 315 is quite gas rich and that accretion of gas from the
environment is quite likely.[astroph/0908.3951]
Authors:
R.Morganti(1,2), A.B.Peck (3,4), T.A.Oosterloo (1,2), G.vanMoorsel (4),
A.Capetti (5), R.Fanti (6,7) ,P.Parma (6) and H.R.deRuiter (6,8)
1 ASTRON,
2 Kapteyn Astronomical Institute, University of Groningen,
3 Joint ALMA Office,
4 NRAO, Socorro,
5 Osservatorio Astronomicodi Torino,
6 INAF, Istituto di Radioastronomia,
7 Dipartimento di Fisica dell' Universita di Bologna,
8 Osservatorio Astronomico di Bologna
Caption: Continuum (contours) and column density (grayscale) of the broad (left) and narrow (right) H i absorption as derived from the VLBI observations. The intensity scales given on the right side of each panel are in units of 1020 cm-2 . The contours of the continuum are 2, 4, 8, 16, ... mJy beam-1. |
According to a well-established paradigm, the activity of galaxies can be
recurrent. The signature of a renewed activity is most convincing if a
large, double-lobed relic structure straddles a pair of young lobes giving
rise to the so-called double-double radio source (DDRS). Typically, the
separation of the outer lobes in DDRSs is not greater than one order of
magnitude that of the inner lobes. It may happen, though, that the inner
part is too compact to be properly imaged in the maps encompassing the outer
one and so, as a whole, the source does not appear as a DDRS but as a
core-dominated triple (CDT), where the alleged core is actually a compact,
luminous double source. Of course, not every CDT will turn out to be a DDRS
when its core is magnified, but B0818+214 was a likely candidate for a DDRS.
Fig. 1 shows its overall structure as seen in FIRST.
To reveal the nature of the "core" of B0818+214, we launched an 18-cm
observation using the EVN combined with MERLIN. 14 antennae, including
the largest two: Lovell and Effelsberg, took part in the project (EM063).
Four hours of observing with 41 baselines produced a very good, uniform u-v
coverage and good sensitivity: the noise in the resulting image was ~40
microJy/beam. The resulting image is shown in Fig. 2. The "core" of
B0818+214 is actually a double, well aligned with the outer double seen in
the FIRST image. Can B0818+214 be labelled a DDRS then?
To answer this question we measured the flux densities of all components
in the most recent EVN+MERLIN L-band image and an earlier MERLIN-only
C-band image, and calculated the spectral indices. They make it clear that
the southeastern feature of the inner structure is an FRII lobe. The
morphology and steep spectrum of the northwestern region leaves no doubt
that it is a lobe as well. All in all, the inner double is a mini-FRII and
B0818+214 as a whole, indeed, fulfills the criteria of a DDRS. However,
given that the linear size of the inner pair is less than 5.7 kpc, the
inner-to-outer size ratio amounts to only 1:100 - an order of magnitude
less than in standard DDRSs.
There is yet another characteristic that makes B0818+214 a special object.
The majority of well-known DDRSs, apart from two pairs of lobes, have a
core. We have found no core in B0818+214. This could mean that the energy
transport from the core has ceased. The assumption that the double radio
source in the centre of B0818+214 is in the coasting phase leads to the
conclusion that the behaviour of the active nucleus in B0818+214 fits two
different evolutionary tracks. On the one hand, its outer lobes resulted
from a long phase of activity interrupted due to e.g. ionisation instability
operating on longer timescales. On the other hand, in the most recent
activity cycle, the central source is intermittent due to radiation-pressure
instability operating on much shorter timescales. Hence, it appears that two
accretion disk instability mechanisms, ionisation and radiation-pressure
driven, could be at work in the same radio galaxy.
Authors:
A. Marecki & M. Szablewski (TCfA), A&A in press, arXiv:0909.3741
Fig.1: In the FIRST image, B0818+214 appears as a core-dominated triple. But what is the true nature of that bright "core"? |
Fig.2: EVN+MERLIN L-band image of the central component of B0818+214. It turns out to be an FRII-like double, a hundred times more compact than the whole radio source. |
In recent years real-time, long-baseline, radio interferometry over optical
networks has developed from a technical possibility to a mature technique.
Scientifically, real-time operation is more important for long baselines,
with their high spatial resolution, than for short baselines. However, until
recently the required technology has not been readily available. Technical
advances and the explosive increase of connection capacity have now radically
changed the situation. Emerging radio interferometers (e-MERLIN, E-LOFAR, e-EVN
and other e-VLBI arrays) do and will exploit mixed private/shared networks to
achieve wide-bandwidth real-time operation. Mirroring developments in other
wavebands of astronomy, these new real-time radio instruments are being optimized
to study transient phenomena. Moving data transport to fiber also gives the prospect
of rapidly expanding observing bandwidth and sensitivity as network capacity continues
to increase. Technically and operationally today's e-VLBI instruments serve as
precursors to the real-time Square Kilometer Array. People working on the science and
technology of real-time, long-baseline radio interferometry met together in Madrid and
Yebes (Spain) to discuss the state-of-the-art and future prospects.
Specific areas covered included:
The National Geographical Institute (IGN) of Spain, in cooperation with the EXPReS project,
hosted the conference at the premises of the National Astronomical Observatory in Madrid
(Spain). One full day was spent at the Center for Technological Development in Yebes.
Participants had a chance to visit the historic site in Madrid, plus the 40-m radiotelescope
and all laboratories (in particular the LNA's one) in Yebes.
Because many experts were present, discussion panels on future organisation/multiwavelngth
coordination to maximize science impact of e-VLBI, network issues, and VDIF specifications,
were organized.
A meeting of the Internet (academic) national providers (NREN) took place on Thursday, as
part of the workshop regular agenda. Chaired by the DANTE representative, John Chevers,
issues on coordination of the European GEANT high capacity data transport infrastructures
with the NRENs, who provide connectivity to the VLBI radiotelescopes, were discussed, as
well as links to non-european partners such as Australia, of great impact to the scientific
return of the e-VLBI network.
A meeting of the EVN Program Committee was held in parallel to the conference, on June 24th 2009.
The proceedings of the EXPReS09 conference will be published soon in "Proceedings of Science"
(PoS; http://pos.sissa.it/).
Authors:
Francisco Colomer (OAN-IGN, Spain), Laura Barbas (OAN-IGN, Spain), Jean-François Desmurs (OAN-IGN, Spain),
Yvonne Kool (JIVE), Rebeca Soria (OAN-IGN, Spain), Charles Yun (JIVE, EXPReS09 conference LOC)
|
|
The next generation EVN correlator will have to be at least a factor of
100 more powerful than the current MarkIV correlator. The new ALMA, EVLA,
E-MERLIN and KVN correlators are all based on more modern versions of the
MarkIV concept, using mainly custom-made chips (ASICs). Because of the
very long development times and the high cost of such systems,
alternatives are actively being investigated.
Of late, software correlators have seen a lot of attention, and several
institutes have, or are planning to, purchase compute clusters for this
purpose. In spite of the obvious advantages such as flexibility and ease
of installation and maintenance, it is not clear that a software
correlator will actually scale to the size of future instruments such as
the e-EVN and other SKA pathfinders. In terms of power consumption,
cooling and processing power versus physical volume Field Programmable
Gate Arrays (FPGAs) perform far better.
In 2009 two projects aimed at developing an FPGA-based next-generation EVN
correlator, both led by JIVE, kicked off. The first, UniBoard, is a Joint
Research Activity within the RadioNet FP7 project. This JRA, with 7
partners in 5 countries (JIVE, ASTRON, Universities of Manchester, Orleans
and Bordeaux, Arcetri and KASI) and a total budget of nearly 2 Meuro, will
develop a generic high-performance FPGA-based computing platform, with a
number of different personalities. These are an EVN correlator, an Apertif
correlator plus beamformer, a digital receiver and a pulsar binning
machine.
The project started on the first of January 2009. Hardware development,
lead by ASTRON, is right on track, and the first prototype board is
expected by the end of this year/beginning of next. The firmware
development for the different applications is ramping up, and work has
started on a generic software interface and a correlator control system.
In parallel to this effort, JIVE and ASTRON have obtained an NWO
(Netherlands Science Foundation) grant for a project called ExBox. This
project will create an EVN/Apertif correlator system by combining several
FPGA-based correlator boards via a backplane, where the intention of
course is to use the UniBoard as a building block for this system. Both
projects are well underway and making good progress.
Arpad
Szomoru (JIVE)
In July 2009 during the slow summer months Metsähovi disspelled the myth
of VLBI data non-compressibility. Particulary data with more than 2 bits can
benefit from lossless compression. Depending on the input distribution and bit
resolution up to 25% compression is possible. Best compression on 8-bit VLBI
data can be achieved using the FLAC lossless audio codec. For tools and
results see bit-dd at http://bdd.sourceforge.net and Esa Turtiainens memo at
www.metsahovi.fi/en/vlbi/misc-hardware/MiM31aug09_Compression_of_VLBI_data.pdf
In June 2009 we released the first 'mark5cEmu' software version. Written entirely in Python, the server allows FieldSystem
control and user can present any networked computer as a running Mark5A, Mark5B or Mark5C unit. The software for example
translates scan recording commands and invokes user recording applications such as Metsähovi's iBOB and VDIF network capture
programs and legacy PCEVN recording programs.
Mark5cEmu v1.0.0 can be found at the end of
www.metsahovi.fi/en/vlbi/ibob/4gexpres.
The mark5cEmu server is of particular interest for easy FS-controlled data capture. For capture you can use systems such as the
BackBlaze 45-disk 90TB storage computer (2000 EUR enclosure and system w/o disks) or the Metsähovi 10/20-disk 40TB storage
diskpack 4G-EXPReS (340 EUR diskpack, 60 EUR PCIe card, 20 * 90EUR disks).
Jan Wagner (Metsähovi Radio Observatory)
|
The Kunming 40-m and Miyun 50-m radio telescopes are two new Chinese VLBI facilities
(Fig.1). They were commissioned in 2007 as key elements of the VLBI support
to the first Chinese lunnar mission Chang'E-1. The Kunming telescope is situated on
Phoenix Mountain (102.80 E, 25.17 N, 1985 m above sea level),
just east of the city of Kunming, Yunnan Province. The Miyun telescope is located at
Bulaotun (116.9 E, 40.5 N, 155 m above sea level), a little
town in Miyun County, about 140~km NE of Beijing.
|
|
Fig.1:
Left: the Kuming 40-m radio telescope; right: the Miyun 50-m radio telescope.
|
This last summer, JIVE organised two experiments to test EVN compatibilities
with the two Chinese new telescopes. On 17 Jun 2009, the Kunming telescope
participated for the first time in an EVN observation during the
network monitoring experiment N09SX1.
Fringes were successfully obtained by the EVN correlator at JIVE to a
number of EVN telescopes (Ef, Mc, On, Ur, Nt, Sh) at S band.
In addition, the Kunming and Miyun telescopes participated
in the X-band experiment EY008A observed on 5-6 Aug 2009, leading to
the first EVN fringes to Miyun, and the first X-band fringes to Kunming.
Results from these two new Chinese telescopes can be seen in the standard
plots for these two experiments on the EVN archive
archive.jive.nl/scripts/arch.php?exp=EY008A and
archive.jive.nl/scripts/arch.php?exp=N09SX1
and via their ftp fringe-test plots
(
www.evlbi.org/tog/ftp_fringes/ftp.html).
Fig.2 shows the u-v coverage of the source J1756+5748 with an
array comprising the available EVN telescopes at X band and the two new
Chinese telescopes. Their addition improves the EVN u-v coverage
considerably, especially on the long baselines.
As part of the experiment CLEP (China's Lunar Exploration
Program, www.clep.org.cn)
with the Chang'E-1 spacecraft, the
two telescopes saw their first light three years ago. Currently, each telescope
is equipped with an S/X band VLBI observing system consisting of a cooled RCP
receiver, an IF distributor with two outputs, eight baseband converters, a VLBA
formatter, a Mark5A recorder, a H-Maser, and a GPS receiver. A computer running
the field system is also used to control all the VLBI devices except for the
antenna and to monitor the system performance at each station. A Mark5B+ and
a Chinese data acquisition system (similar to the digital BBC) have been
installed recently. The new backend is expected to be used in routine VLBI
observations beginning from the next year. Moreover, a L-band receiver
will be equipped with the Miyun telescope in the next year.
The two telescopes successfully tracked the Chinese Chang'E-1 lunar satellite
with the other two older Chinese telescopes, Seshan and Nanshan, and received
the spacecraft downlink data in 2007--2008. In addition, the Kunming station staff
is now working on pulsar observations;
the Miyun station has joined the "Meridian Project" to study the interplanetary
scintillation with an UHF receiver. Although both telescopes have not yet
officially joined the EVN, potential users are encouraged to consider
including them in their observing proposals.
We anticipate continuing advances in their capabilities and participation in
a growing number of EVN experiments. The tools available to the users
(e.g., SCHED, EVN status table, EVN calculator) would
keep abreast of these developments.
More information can be provided by Longfei HAO (haolongfei@ynao.ac.cn) at
Kunming station and Xinying ZHU (zhuxy@bao.ac.cn) at the Miyun station.
The EVN community congratulates the staff at the Kuming and Miyun stations
and looks forward to a lengthy and fruitful collaboration.
J. Yang, L.I. Gurvits, and R.M. Campbell (JIVE)
Fig.2: The u-v coverage of the source J1756+5748 with EVN+Kunming+Miyun at X band. The used EVN telescopes: Mc, On, Ur, Sh, Nt, Mh, Ys, Ef, and Wb; the red points: baselines to Km and My. With the two telescopes, the u-v coverage is significantly improved. |
Recirculation is a means of time-sharing correlator resources for
experiments that don't use the maximum sampling rate. The correlator
"runs" at 32 MHz, fast enough to handle Nyquist-sampled 16 MHz subbands.
In observations using narrower subbands, the correlator chips processing
a specific baseline/subband/polarization will be idle for some fraction
of the time. Recirculation is a means to take advantage of those idling
times to process a different baseline/subband/polarization. Following
some final testing, we have correlated the first user experiments (from
session 2/2009) involving recirculation.
From the astronomer's viewpoint, the advantage of recirculation is
that it can increase the apparent correlator spectral capacity in
experiments that otherwise would have had spectral resolution limited by
the number of stations or polarizations. You may recall (from the web site,
from correlator talks at EVN symposia) that the correlator capacity
formula was:
5-8 stations
5-8 stations
9-16 stations
9-16 stations
|
1 SB
1 SB
1 SB
1 SB
|
1 pol
4 pol
1 pol
4 pol
|
2048 frq.pt
512 frq.pt
512 frq.pt
128 frq.pt
|
bbfilter =
|
16MHz
8MHz
4MHz
≤2MHz
|
R = 1
R = 2
R = 4
R = 8
|
5-8 stations
9-16 stations
9-16 stations
|
2 SB
1 SB
1 SB
|
4 pol
2 pol
4 pol
|
2048 frq.pt
2048 frq.pt
1024 frq.pt
|
Of course, you can't have everything for free. A possible downside
to recirculation is that it will tend to increase the shortest possible
integration time by a corresponding factor of R. This comes about because
the correlator is producing more than "one correlator's worth" of output
per integration time, which all still needs to be read out. This increase
in the minimum integration time with recirculation could affect spectral-line
experiments with >8 stations and/or cross-pols desiring a larger field-of-view
(i.e., reduced time smearing). Without recirculation, the minimum integration
time for the whole correlator is 0.25s.
We've revised the correlator capacity page on the web to reflect the
availability of recirculation:
www.jive.nl/correlator/status.html
Viewgraphs about both the spectral and output capacities have been added
as further links.
R.M. Campbell (JIVE)
The EVN pipeline is an automated script written in Python, using
ParselTongue to access AIPS tasks. Among other things, it applies an
a priori amplitude calibration using the system temperatures and gain curves
from the stations, fringe-fits (a subset of) sources, applies bandpass
calibration, and makes preliminary CLEAN images using either iterations of
phase and amplitude self-cal or phase-referencing. It saves a set of
AIPS tables from various stages of the calibration/fringe-fitting process,
which the PI can later apply to the raw data if desired. The pipeline results
are available on the EVN Archive, following the standard one-year proprietary
period data-release policyfor plots/images of sources identified by the PI
as "private".
UV FITS files that include the cumulative calibration resulting from
the pipelining are also now available for individual sources on the EVN Archive.
The link to these calibrated FITS files can be found at the bottom of the
table shown in the main pipeline page for each experiment (per pass, if
applicable). The calibrated FITS files associated with "private" sources
are protected by the same one-year proprietary period as are the plots/images
of these sources and the full set of raw IDI FITS files.
R.M. Campbell (JIVE)
The EC funded EXPReS Project concluded on schedule at the end of August 2009.
Over the past 42 months, operational e-VLBI has moved from a heroic-effort
demonstration to a regular, supported and reliable service. In this period,
network connectivity to telescopes was established and improved, the EVN
correlator, originally designed to handle tapes in batch-type operations, was
transformed into a real-time instrument, numerous new software tools were
developed for monitoring and feedback purposes, research into tools were
developed to monitor e-VLBI (disk based observation as well) and
next-generation correlation techniques were investigated. e-VLBI has become an
operational service with multiple papers published and hundreds of hours of
stable observations.
The 19 member consortium brought together the network engineers, computer
scientists and astronomers necessary to make the move into e-VLBI. Our
international partners provided long baselines, using the fast, long-distance
networks. The new EXPReS Network Map displays our partner telescopes and the
network connections that bring the data to the correlator at JIVE.
The project has cleared all of the major technical hurdles and is now preparing
for the final project review. We are proud of our accomplishments and look
forward to upcoming activities which will expand and improve upon the work
pioneered by EXPReS.
EXPReS is an Integrated Infrastructure Initiative (I3), funded under the
European Commission's Sixth Framework Programme (FP6), contract number 026642.
For additional information, you can visit the EXPReS website at
http://www.expres-eu.org/.
The
EXPReS team
|
The present analog VLBI data acquisition hardware at the EVN (and other)
telescopes is in general more than 20 years old. The Onsala system was
installed in 1979. It was the first MK III terminal in Europe. It has been
used for observations since November 21-26, 1979. The Effelsberg terminal was
installed in 1982. Other "European" systems were installed soon after.
Although some upgrades were applied like wider filters, a new decoder and a
new formatter, the core of the acquisition system is still the same old
hardware.
For a few years a small team from Noto and Bonn under the leadership of Gino
Tuccari has been working on the hardware and the firmware of a digital
replacement for the analog acquisition systems, which is called DBBC (digital
Base Band Converter). Recently more people have joined the project
e.g. Metsähovi, Shanghai and Arcetri for the development of firmware and
people from Wettzell and NASA/GSFC (Ed Himwich) for writing DBBC control
software for the Field System (FS). The FS is used to execute all VLBI
observations and thus has to be able to handle the DBBC.
First prototype units have been installed at Wettzell and Effelsberg. Soon
Noto will follow. Together with the installation of a DBBC the VLBI disk
recorders have to be upgraded from Mark 5A to Mark 5B.
The development of the DBBC is now nearing its end and thus a small company -
HAT-Lab (http://www.hat-lab.com/ under construction) - has been founded for
the production of DBBCs. Interested institutes can get quotes for DBBCs in
different configurations as required at telescopes which observe astronomy
projects or also geodetic experiments.
New capabilities of the DBBC will be better shapes of bandpasses, wider
sub-bands, continuous calibration and higher bitrates. In addition the phases
of sub-bands will line up without any calibration phases.
The so-called poly-phase filterbank firmware has successfully been tested and
compared to the Haystack Digital BackEnd (DBE). The downconverter firmware
will see its final tests this year. In a few months a 10 Gb Ethernet
interface for the DBBC will become available. Together with an upgrade of the
reocorders to Mark 5C, maximum datarates of 4 Gbit/s will become possible.
Walter
Alef
2009
Session 2: 28 May - 18
June
Wavelengths: 5, 18, 6, 13/3.6 cm
This was another full length session, and the first for some time
without any global projects (at least since June 2002 when the present
scheduler came to office !). 4 observations involved Arecibo. 5
observations used an incomplete MERLIN array. There was only a single
user project at 13/3.6 cm. One project was correlated at the Bonn
correlator and the rest at the EVN correlator at JIVE.
A total of 25 observations from 11 proposals was scheduled. Yebes was
scheduled for the first time at 6cm. The Yamaguchi (Japan) antenna was
added to one of the 5cm projects.
Disk space usage in recent sessions
Session |
Space |
2007 Session I |
373.7 TB |
2007 Session II |
305.2 TB |
2007 Session III |
260.4 TB (no Chinese antennas) |
2008 Session I |
411.6 TB |
2008 Session I |
411.6 TB |
2008 Session II |
451.3 TB |
2008 Session III |
508.0 TB |
2009 Session I |
474.7 TB |
2009 Session II |
556.0 TB |
2009 Session III |
595.0 TB |
Recent eVLBI runs:
Date |
l |
Duration |
|
19MAY09 |
18cm |
24h |
2 normal proposals + 1 ToO + 1 trigger proposal (not triggered)
|
27AUG09 |
6cm |
--- |
test run only |
10SEP09 |
18cm |
15h |
2 normal proposals |
29SEP09 |
18cm |
10h |
1 normal + 2 short + 1 trigger proposal
|
Dates for EVN sessions in 2010 agreed by the EVN CBD are as follows:
Session |
Date |
2010 Session I |
Mar 4 - Mar 25 |
2010 Session II |
May 27 - Jun 17 |
2010 Session III |
Oct 21 - Nov 11 |
Due to the planned introduction of the new WIDAR correlator at the VLA
in January 2010, it is "prudent to assume that neither Y1 nor Y27 will
be available" for an indefinite period thereafter.
Richard Porcas (EVN Scheduler)
Mehreen Mahmud joined the Science Operations and Support Group at JIVE
as a Support Scientist at the beginning of August, after completing her
thesis work at the University of Cork. Yurii Pidopryhora also joined
the group as a full-time Support Scientist at the beginning of September.
For a few months prior to this, he had been splitting his time between the
group and the EXPReS project, for which he had previously worked exclusively.
The arrival of these two new support scientists brings the group up to
full strength for the first time since the end of last year. The chances
are good that you may be interacting with them in the course of your
experiments in the near future.
The first fringes have most likely been detected in baselines between Exloo
and the first international LOFAR station of the MPIfR (Bonn) in Effelsberg
(ca. 250km).
The observations were prepared for the first "LOFAR Imaging Busy Week" (17-21
August 2009) by George Heald, Ger de Bryun and John McKean at ASTRON.
The low band antennas (LBA) observed 3C196 for 2.5 hours on 20 August using 72
subbands of 195 kHz each, subdivided into 256 channels. The bands were
uniformly spread over the frequency range 31-73 MHz.
James Anderson (MPIfR) and Neal Jackson (Manchester) were the first to examine
frequency-averaged data on baselines to Effelsberg, claiming
a possible weak detection of periods with coherent phases, but without any
certainty.
After detecting peaks in averaged one-dimensional delay-spectra, Olaf Wucknitz
(AIfA, University of Bonn) produced time-dependent two-dimensional delay/rate
spectra of single bands that already show clear signals on short and
international baselines (see Fig. lofar_1a and lofar_1b).
The ad hoc software was then extended to derive coherent multi-band delays,
which also allowed to disentangle dispersive and non-dispersive delays and
rates. Fig. lofar_2 shows the results as function of time for the usable
100min of data. The flux variations are probably due to the beating of the two
source components (separation 6arcsec). The delay is dominated by a
non-dispersive contribution (probably a clock offset of ca. 1.3 microsec) and
furthermore shows a time-variable dispersive part due to the ionosphere
(0.1-0.4 microsec).
The phase-rates, on the other hand, are consistent with being purely
dispersive.
Shorter baselines (not shown) have constant non-dispersive delays of
the order 0.1 microsec and dispersive time-variable rates.
We consider this as a clear detection that is entirely consistent with the
expectations. Later observations with 12-hour tracks are currently being
analysed in order to confirm (or disprove) the findings.
More information is available at
www.astro.uni-bonn.de/~wucknitz/lofar/firstfringes.php and in an
upcoming press release of MPIfR and ASTRON.
Olaf Wucknitz (AIfA Bonn)
on behalf of the LOFAR Long Baseline Working Group
(Anderson, Conway, Jackson and others) and the Effelsberg station team
(Anderson, Kramer, Reich, Zensus and others).
|
|
Caption: Delay/rate spectra movie covering ca. 1h for one subband around 69 MHz on a short (RS106-RS307) and international (DE601-RS106) baseline of LOFAR. |
Caption: Flux (in arbitrary units), delay and rate as function of time for an international LOFAR baseline. These werde determined from peaks in coherently combined delay/rate spectra of most subbands. The convention for the dispersive delay was chosen so that the sign of the group delay is consistent with the non-dispersive delay. The rate thus corresponds to the negative time-derivative of the delay. |
With this issue of the EVN Newsletter we start this new section, which can be
called a 'meeting point'.
The EVN community is a dynamic body: new people coming in, new stations are going to join
the EVN and many of us are in this business from the beginnig but are faceless for many others!
We thought we should know each other better. We start with the Torun EVN station
and community. Here you can find a few photos of people there and of the observatory.
Please, send me your opinions about this meeting point and if you like it, send me photos of you and your
observatories. Future issues of the EVN Newsletter need not be limited to photos
nor to one station only!
Magdalena Kunert-Bajraszewska, EVN Newsletter Editor
Andrzej Kus, Director of TCfA and a new Chairman of the EVN Consortium Board of Directores |
Marian Szymczak, Head of the Radioastronomy Dept., scientific interests: masers; Kaz Borkowski, VLBI Friend; Andrzej Marecki, scientific interests: AGNs, double-double objects |
Magdalena Kunert-Bajraszewska, CBD Secretary and Newsletter Editor, scientific interests: AGNs, CSS sources, BAL quasars |
First day of autumn: Anna Bartkiewicz, scientific interests: masers, and Marcin Gawronski, scientific interests: AGNs, Hybrid objects |
EVN Newsletter No. 24.
2009 European VLBI Network. Edited by Magdalena Kunert-Bajraszewska (TCfA, Poland).