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European VLBI Network Newsletter Number 23 May 2009 |
On 3-5 April 2009 the EVN organized e-VLBI demo observations in the
frame of the event "100 Hours of Astronomy", a cornerstone project of
the International Year of Astronomy 2009. Fourteen stations participated in the
observations:
In fact, at the occasion of the "100 Hours of Astronomy", the
Yebes 40-m dish obtained its first e-VLBI fringes
by using the new 1 Gbps connection to GEANT2
installed at the observatory in the frame of the FP6 EXPReS
project. This is an important milestone both for the EVN and the Yebes observatory.
The EXPReS team is organizing now the 8th
International e-VLBI workshop on Science and Technology of Long Baseline
Real-Time Interferometry. This workshop will be held in
This Newsletter contains some exciting scientific results obtained with
the EVN, in this case mostly on extragalactic Astronomy. As these results show, our Network is
providing astronomers with a very detailed view of some of the most energetic
phenomena in the universe.
At the time of writing these lines, the news coming from the development
of the European digital BBC's is very good. A spin-off company has been put
in place to commercialize these devices that should form part of most EVN
stations in the near future.
The EVN Board of Directors will meet at Onsala
in May 26-27. We all look forward to a friendly and positive meeting as it is usual
for the group. At this meeting, in addition to discuss about the policy,
operations, and technical developments of the array, we also plan to discuss
with our colleagues from China and Russia in view of the possible strengthening
in the collaboration with the stations of Kumming and
Miyun (China) and with the KVASAR network (Russia).
After two years of serving as the Chairman of the Consortium Board of
Directors, my mandate will arrive at his end at the next meeting in Onsala. I am pleased to announce that the board will
propose Andrzej Kus,
director of CfA (
Rafael Bachiller (OAN,
(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.
2009 Session 3 |
Oct 22 – Nov 12 |
18/21cm, 1.3cm, 6cm, 5cm, 7mm, … |
2010 Session 1 |
Feb 1 – Mar 18 |
18/21cm, 6cm, … |
The dates
for Session 1 2010 are still provisional.
Proposals
received by 1 June 2009 will be considered for scheduling in Session 3, 2009 or
later. Finalization of the planned observing wavelengths will depend on
proposal pressure. 3.6cm observations may also be scheduled in Session 3 2009.
2009 Aug 27 – Aug 28 (start at 13 UTC) 2009 Sep 10 – Sep 11 (start at 13 UTC) 2009 Oct 15 – Oct 16 (start at 13 UTC) 2009 Nov 19 – Nov 20 (start at 13 UTC) 2009 Dec 01 – Dec 02 (start at 13 UTC) 2009 Dec 10 – Dec 11 (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 |
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 June 1st deadline to be considered for scheduling in
the above e-VLBI sessions starting from August 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.
Please consult http://www.evlbi.org/evlbi/e-vlbi_status.html for
the current e-VLBI array and for the availability of different eVLBI stations per observing band and for the dates of
the e-VLBI observing sessions.
Yebes 40-m is now
part of the regular EVN sessions at 5/6cm, 1.3cm and at S/X.
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 2009 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 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 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
Cygnus
A is the closest (z=0.057) strong FRII radio galaxy and therefore a key object
for detailed studies of its prominent double sided jet and nucleus. Owing to
the large inclination of the jet with respect to the observer (>75 deg), and
correspondingly reduced relativistic effects, Cyg A
is an ideal candidate for detailed studies of its jet physics, which is thought
to be similar to those in the more luminous quasars.
Our
previous studies revealed a good kinematic model for the jet of Cygnus A, but
the counter-jet speed is still not well constrained. The central engine and
part of the counter-jet of Cyg A are likely to be
obscured by free-free absorbing material, presumably a thick torus. Because at
mm-wavelengths, the absorber becomes optically thin we started to monitor Cyg A with global VLBI at 43 GHz in October 2007. To obtain
the highest possible sensitivity and resolution a global VLBI array of 15
antennas, including the VLBA, GBT, VLA1, Effelsberg, Onsala, and Noto, at 43 GHz with
a recording rate of 512 Mbps is used to image Cygnus A on four successive
epochs separated by about 8 month. The data from first two epochs were
correlated at JIVE. The image of Cygnus A reveals a previously unseen gap
between both jets (see Figure). This could either indicate the emergence of a
new counter-jet component that is slowly separating or we start to see the very
inner acceleration region of the jet which is not efficiently radiating at
radio wavelengths. Another alternative could be that the gap is caused by some
absorbing material, e.g. a dense sub-pc size torus surrounding the nucleus.
Analysis of the second epoch from October 2008 is in progress and will show
whether the gap shows any time evolution or if it is a stationary feature.
Further more the image above shows transversely resolved jet structures at
distances beyond ~0.5pc (see Figure).
Analysis
of the resolved jet structure shows that the initially wide jet (opening angle
~10deg) collimates within the first parsec into an edge-brightened jet with an
opening angle of ~3deg. For more details see also PoS(IX EVN Symposium)108 at http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=72.
Authors: U. Bach
(1), T.P. Krichbaum (1), E. Middelberg (2), W. Alef (1), J.A. Zensus (1)
((1) MPIfR,
Bonn, Germany, (2) Astronomisches Institut - Ruhr Unsiversität, Bochum,
Germany)
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Dutch
school teacher, Hanny van Arkel,
discovered what is surely one of the most bizarre objects uncovered via the
GalaxyZoo.org morphological census (Lintott et al.
2008, . Jozsa, Garrett & Osterloo
et al. 2009), SDSS J094103.80+344334.2. This object, now known as “Hanny’s Voorwerp”, appears as an
irregular cloud located 15 ? 25 kpc in projection
from the massive disk galaxy IC 2497 (see Figure 1, Jozsa,
Garrett et al. 2009) and has a redshift matching with
the galaxy (Vsys = 15056 ± 40 km/s, taken from the
NASA Extragalactic Database NED) to within 300 km/s (Lintott
et al. 2009).
This
object is highly ionised and has a spectrum dominated
by emission lines, particularly [O III] (Lintott et al
2009). What is most peculiar is that X-ray observations carried out by the
Swift satellite, have not indicated any ionisation
source in the galaxy or the object (Lintott et al
2009). With this, only two possible hypotheses are left. Ether an AGN exists in
IC 2497 and is heavily obscured but sill able to ionise
the Voorwerp or else the ionising
source is no longer present and the Voorwerp is the
result of a light echo being seen from an AGN that has "turned off" (Lintott et al 2009).
To
determine which of these scenarios is most likely responsible for the Voorwerp, we observed IC 2497 with the e-VLBI on September 30, 2008. The e-VLBI observations
were conducted by the European VLBI Network (EVN) at 1.650 GHz. The array
included the Westerbork, Medicina,
Onsala 25-m, Torun, Effelsberg,
Jodrell Bank MkII, and Darnhall telescopes. The observing bandwidth was 64 MHz in
both LCP and RCP and 2-bit sampling was employed, resulting in a total data
rate of 512 Mbps for each telescope. The total observing time was approximately
2 hours from UT 12:06:23 to 14:18:17 of which approximately 1.5 hours were
"on-source". For the observations, the target was phase-referenced to
J0945+
During
the editing, imaging and calibration process, it was found necessary to discard
the Jodrell Bank - Darnhall
baseline, probably due to correlated interference. The calibration solutions
derived from J0945+3534 (including phase and amplitude corrections obtained by
hybrid mapping the source) were then applied to the IC2497 data. Using natural
weighting, a compact radio source at the centre of IC2497 was clearly detected
from the phase calibrated data set.
The
e-VLBI image of IC2497 is shown in the Figure. A compact source was detected at
a position of RA 09 41 04.087 and Dec. 34 43 57.778 (J2000). This observed
position is offset by approximately 135 milliarcseconds
to the south west of the VLA FIRST source (R.A. 09 41 04.094 Dec. +34 43 58.000
(J2000)). This offset represents a shift of approximately 1/50th of the VLA synthesised beam. The source appears marginally resolved in
the VLBI map but this may be due to residual phase errors after phase
referencing. The total integrated flux density measured is 1.0934E-03 ± 1.31E-04
Jy, which represents only 6% of the total VLA First
flux density measurement (16.83 mJy). Measurements of
the size of the VLBI component using IMFIT suggest the size is < 60 milliarcsecond. From this, we determine a limit on the
brightness temperature of the source, Tb > 4E05 K.
This
strongly suggests that an obscured AGN is present within the core of IC2497.
This, together with the WSRT detection of larger scale jet emission, suggests
that the AGN is associated with a jet that clears a channel through the galaxy
towards the Voorwerp (see Fig 1). This cleared
channel permits the AGN to ionise the large reservoir
of gas surrounding IC2497 and the result is Hanny's Voorwerp.
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Caption: WSRT observations reveal a radio jet (white contours)
emanating from the centre of the nearby galaxy IC 2497, headed straight in
the direction of Hanny's Voorwerp
(green). The observations also reveal a huge reservoir of hydrogen gas (coloured orange) that probably arose from a previous
encounter between IC2497 and a group of galaxies that are now located due
west of the Voorwerp. The e-VLBI observation
(right) indicates the presence of an AGN at the centre of IC2497. The cross
shows the VLA FIRST position, with respect to the e-VLBI detection. Credit:
Main image left (Josza, Garrett & Oosterloo et al. 2009). Hanny's
voorwerp (bottom right) Dan Herbert, Isaac Newton
Telescope. |
H. Rampadarath (JIVE & Leiden Univ), M.A. Garrett (ASTRON, Leiden Univ
& Swinburne University), G.I.G Jozsa (ASTRON),
T.A. Oosterloo (ASTRON & Univ. Groningen), Z. Paragi (JIVE).
Coeval growth of the bulge and the central massive black hole of AGN is
supposed to be regulated by fueling and feedback. The details of the underlying
physics are still under debate. High angular resolution observations can shed
light on the nuclear structure of AGN and can help disentangling the associated
energy dynamics into nuclear and stellar components. We have therefore carried
out MERLIN/EVN
Jens Zuther, Sebastian Fischer, Andreas Eckart
I. Physikalisches Institut, Universität zu Köln
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Figure caption: 18cm cleaned maps (preliminary) with MERLIN (left) and
western EVN (right) of three targets of our sample. Contours refer to -1 (in white),
1, 2, 4, 8, 16, … (in blue) times the rms in the
image (Zuther, Fischer, & Eckart
in prep.). The beam sizes are indicated in the bottom left of the images. The
image size is 4 x 4 arcsec2 and 0.2 x 0:2 arcsec2, respectively. North is up,
East is left. |
Quasars at the highest redshift (z~5 or more)
place strong constraints on the early cosmological evolution of active galactic
nuclei (AGNs) and the growth of the supermassive black holes. The AGN activity observed at high
z indicates that AGN feedback processes may have played an important role in
the early galaxy and cluster evolution. The ultimate evidence for AGN jet
activity is provided by VLBI observations. Our recent results for compact radio
sources at z~6 (J0836+0054 and J1427+3312; see http://www.oan.es/evnnews/evnnews20.html#z6)
indicate that there is a steep-spectrum population of the most distant radio AGNs.
Only eight radio quasars at z>4.5 have been studied with VLBI prior
to our experiment. Our aim was to increase this sample, by selecting optical
quasars at z>4.5 from the Sloan Digital Sky Survey (SDSS), unresolved
(<5") in the VLA FIRST survey at 1.4 GHz, with total flux densities of
~10-30 mJy. Earlier experience with the EVN (see http://www.oan.es/evnnews/evnnews19.html#devos)
taught us that these have a very good chance to be detected at mas scales in the radio. Indeed,
we could successfully image all the five such SDSS/FIRST quasars we found and
proposed. The EVN observations in experiment EF021 took place on 22 and 29
October 2008 (at 5 GHz and 1.6 GHz, respectively).
Although the sources are fairly compact, they are typically somewhat
resolved and show mas-scale extended emission.
Interestingly, for 4 out of 5 quasars, the radio spectrum of the innermost
structure between 1.6 and 5 GHz is steep, with a spectral index of about -0.6.
Note that we did not use any a-priori spectral information when selected this
sample, in particular we did not pick up flat-spectrum quasars.
One of the quasars (J0813+3508, z=4.92) has a companion radio source
~7" away that is unresolved in FIRST. Since the ~10-mas scale inner jet
revealed by our new 1.6-GHz image points towards its direction, and we measured
excess flux density on the shortest VLBI baseline indicating some extended
emission on ~0.1" scale, we believe that the companion - which otherwise
is resolved out with the EVN - is actually physically associated with the high-redshift quasar. If this is the case, the full angular
extent of the source corresponds to ~45 kpc projected
linear size.
S. Frey (FÖMI SGO,
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Figure caption: Phase-referenced EVN images of five z>4.5 quasars
at 1.6 GHz (top row) and 5 GHz (bottom row). The sizes of the fields are 120 mas x 120 mas (1.6 GHz) and 30 mas x 30 mas (5 GHz). The
typical restoring beam sizes are 20 mas x 4 mas (1.6 GHz) and 5 mas x 1.5 mas (5 GHz), elongated to the N-S direction. The peak
brightness values range from 11 to 17 mJy/beam (1.6
GHz) and 4 to 9 mJy/beam (5 GHz). The sources (from
left to right): J0813+3508, J1146+4037, J1242+5422, J1611+0844 and
J1659+2101. |
A large project to study the gravitational lens MG0414+
Olaf Wucknitz (
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Composite image by Ros (2000) to give an
overview of the system. This system in special in many ways. A1 and A2 have very
high magnifications (~12), B still has a magnification of ~5. From theory one
would generally expect that A1 and A2 are mirror images of each other. In
this case the slightly different direction of the highest magnification
conspires with the special source structure to produce the very different
shapes. |
Preliminary
results of the observations: all four lensed images
from the current project (GW019B). |
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Left images: current GW019b observations. Right: previous data from Eduardo Ros
(1997). Top: full resolution. Bottom: convolved to about equal resolution. |
100 Hours of Astronomy, a cornerstone project of the International Year of Astronomy
(IYA2009), took place 2-5 April 2009. Following on the success of the marathon,
global e-VLBI
observation for the IYA2009 Opening Ceremony in January, the EVN organized two
e-VLBI runs on 3 and 5 April with the participation of 14 stations:
100 Hours of Astronomy also included "Around the World in 80
Telescopes," 24-hours of live webcasts from observatories around the
world. The EVN was represented by an interview with Huib
in the control room at JIVE, and the recorded webcast can be viewed online at http://www.ustream.tv/recorded/1336875.
The educational e-VLBI web site built by JIVE's Harro Verkouter for IYA2009 is
still available at http://iya.expres-eu.org/
The EXPReS team
In the
framework of the EC funded project “EXPReS” (http://www.expres-eu.org/), the
observatory is connected to GEANT at 1 Gbps. First
e-VLBI fringes were obtained at C-band with the e-EVN during the campaign “100
hrs of Astronomy”, on April 3rd 2009. This is an important milestone
for the whole team involved in the commissioning of the telescope, in
particular because of the successful operation of the antenna, receivers, VLBI
and network equipment.
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Stations
participating in the e-VLBI observations. |
Example
of real time fringes between Yebes and WSRT. |
The first
half of 2009 has been very busy for the e-EVN. Most of the e-VLBI observing
runs were fully packed with experiments, and we had a number of Target of
Opportunity requests as well. The 40-m Yebes
telescope joined the array during the "100 Hour of Astronomy" demo
observations (see above), and it is now part of the regular e-VLBI array.
On
12-13 May 2008 there was a ToO project observed at 5
GHz which went very well. This was the first time that Jodrell
Bank participated at a full 1024Mb/s, thanks to an upgrade of the Mark5
motherboard by Paul Burgess. The Mark5 in question now has 2 network interfaces
of 1Gb/s each, and using the Linux round robin Ethernet bonding driver, the
traffic can be distributed over both networking cards and both 1Gb/s fibers from
JBO to JIVE, as 1024Mb/s of e-VLBI data does not fit in a single 1Gb/s fiber.
There is a second Mark5 at Jodrell Bank, connected to
their VLBA formatter, that receives data from multiple MERLIN outstations and
transmits this data to JIVE as well. Both
After
the science run, several stations helped to test Bob Eldering's
Domino implementation for e-VLBI with a Mark-5B. In this test, we detected
real-time fringes for the first time from a Mark-5B equipped station (Yebes) connected to a Mark-5B at JIVE. Unfortunately, the
Mark-5B IO board stops completely as soon as a single corrupted header frame is
received. We are investigating workarounds for this issue to make this mode
more robust.
The EXPReS team
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After a
period of commissioning in 2007-2008, from Session 2008/3, VLBI-operations in
WSRT make full use of the new digital Tied Array Distribution Unit (TADUmax) system, which in combination with Mark5B recorder
replaces the old analog adding system, the field system and the Mark5A
recording system.
TADUmax has now been successfully used in two full EVN
sessions as well as in a number of VLBI experiments. From EVN Session 2009/3,
the TADUmax-Mark5B combination will also be used when a single dish is used
(e.g. 5cm observations or when a wide field-of-view is required).
The
Mark4 DAS and the Mark5A recorder will be decommissioned soon.
Rene Vermeulen (ASTRON)
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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) 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 optimised to study transient phenomena. Moving data
transport to fibre 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. Given recent developments
the time seems ripe to bring all those working on the science and technology of
real-time, long-baseline radio interferometry together to discuss the
state-of-the-art and future prospects.
The
conference will be held in Madrid (Spain) on June 22nd- 26th 2009. It will
cover both scientific applications (first half) and technical implementation
(second half) with joint sessions in the middle. The conference proceedings
will be published electronically. Specific areas to be covered include:
· Scientific:
Applications of real-time operation to astronomy, geodesy and other
applications. How to best coordinate emerging e-VLBI arrays for best scientific
return. Connections to transient monitoring in other wavebands including Fermi
Gamma-Ray Space Telescope observations.
· Technical:
e-VLBI test experiments, use of new long distance links, development in
techniques including selective packet dropping and novel protocols, the search
for higher bandwidths, network status and monitoring, distributed processing,
and future development.
· Scientific/Technical:
Future technical possibilities of interest in planning future instruments.
Desired technical requirements to fulfill scientific goals, science priorities
for development.
More
than 80 participants have already signed up to attend!
Detailed
information at http://www.oan.es/expres09/
Francisco
Colomer, LOC Chairman.
2009
Session 1: 26 February - 19 March
Wavelengths: 6, 1.3, 18, 5,
This
was a full length session although, as often, days during the 5cm part were
very unevenly filled since nearly all the methanol maser projects required the
same GST range (Galactic Centre). There
were only single user projects in the 1.3cm and 0.7cm part. There were 2 global projects, 3 observations
involving
A total
of 21 observations from 13 proposals was observed. Projects requiring MERLIN were given some
scheduling priority as a number of MERLIN antennas will not be available in session
II. Yebes took part for the first time in the 5cm
part. The Yamaguchi (
Recent eVLBI runs:
Date |
l |
Duration |
|
22JAN09 |
18cm |
21h |
2
normal + 1 short |
10FEB09 |
18cm |
17h |
2
normal proposals + 1 trigger proposal (not triggered) |
21MAR09 |
6cm |
15h |
1
normal proposal + 1 trigger proposal (TRIGGERED !) |
21APR09 |
18cm |
24h |
2
normal + 1 short + 1 ToO + 1 trigger proposal (not
triggered) |
Richard
Porcas (EVN Scheduler)
Since
October 2008, Nicolas Pradel is the "Friend of VLBI" for the WSRT
(email: pradel@astron.nl).
EVN Newsletter No. 23. ©
2009 European VLBI Network. Edited by Francisco Colomer
(OAN, Spain).