European VLBI Network: Present and Future
aa r X i v : . [ a s t r o - ph . I M ] J a n European VLBI Network: Present and Future
J. Anton Zensus ∗ a and Eduardo Ros abc † a Max-Planck-Institut für RadioastronomieAuf dem Hügel 69, D-53121 Bonn, Germany b Observatori Astronòmic, Universitat de ValènciaC. Catedrático José Beltrán 2, E-46980 Paterna, València, Spain c Departament d’Astronomia i Astrofísica, Universitat de ValènciaC. Dr. Moliner 50, E-46100 Burjassot, València, SpainE-mail: [email protected] , [email protected] The European VLBI Network ‡ is a collaboration of the major radio astronomical institutes inEurope, Asia, South Africa and Puerto Rico. Established four decades ago, since then it has con-stantly improved its performance in terms made using resolution, data bit-rate and image fidelitywith improvements in performance, and the addition of new stations and observing capabilities.The EVN provides open skies access and has over time become a common-user facility. In thiscontribution we discuss the present status and perspectives for the array in a continuously chang-ing environment, especially in the era of ALMA and with the Square Kilometre Array ante portas.12th European VLBI Network Symposium and Users Meeting - EVN 2014,7-10 October 2014Cagliari, Italy ∗ Speaker. † The authors are grateful to R.W. Porcas for careful reading of the manuscript and useful comments and suggestions. ‡ The European VLBI Network is a joint facility of European, Chinese, South African and other radio astronomyinstitutes funded by their national research councils. c (cid:13) Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlikeLicence. http://pos.sissa.it/
VN: Present & Future
J. Anton Zensus
1. A very short history of the EVN
After successful VLBI observations using European telescopes in the late 1960s and intra-European observations in the early 1970s, discussions about a European array date back to 1975.After several meetings the European VLBI Network was formally established in 1980. A detaileddescription of the early times of the network has been published in recent conferences [1, 2]. Ini-tially it was a 4-station network (Dwingeloo/Westerbork, Effelsberg, Jodrell and Onsala). From thevery beginning a program committee (the EVNPC) was established and reviewed observing pro-posals submitted 3 times per year. A scheduler to coordinate observations was appointed in 1982,and this task was performed by different individuals at the MPIfR until Alastair Gunn (Jodrell)took this over in 2014.Since 1980 many stations have been added to the network: Medicina (1984), Wettzell (1995),Noto (1989), Shanghai, Metsähovi and Cambridge-32m (1990), Yebes-14m and Urumqi (1994),Torun-32m (1996), Arecibo and Hartebeesthoek (2001), Yebes-40m (2008), the KVAZAR net-work: Svetloe, Zelenchukskaya and Badary (2009), and recently the KVN: Yonsei, Ulsan andTamna (2014). The Sardinia-64m and Tianma-65m will start regular participation in 2015.Data were initially correlated at the MPIfR processing centre in Bonn. The Joint Institute forVLBI in Europe, established in 1993, is currently tasked with data correlation and postprocessingand EVN user support. A new correlator was dedicated in 1998, and in recent years this has nowbeen replaced by a software correlator, SFXC. The EVN has constantly improved its capabilitiessince foundation, both in terms of antenna performance and data bit-rate, from the 4 Mbps providedby the Mk II system in 1980 to the plans for 2 Gbps in 2015 using the Mk V system with digitalbackends.The science addressed by EVN observations has covered a broad range of topics with a highscientific impact. Several hundred refereed papers make use of observations from the network; themost cited works include: • the properties of compact steep-spectrum sources using radio observations at different scales [3] • a study of a sample of radio galaxies [4] • examining the dynamics of the compact symmetric objects 0710+439 and 0108+388 [5, 6] • investigation of methanol masers (a unique EVN capability for many years) [7, 8] • imaging of gravitational lenses such as B0218+35.7 [9] • imaging of radio jets in galactic objects such as LS I +61 ◦
303 [10].Recent publications with the largest number of citations per month report astrometric studies of theMilky Way [11, 12], and feedback in the jet of the radio loud galaxy 4C +12.50 [13].
2. Present EVN
At present the EVN comprises 14 major institutes including JIVE. Overall EVN policy isset by the Consortium Board of Directors. EVN science topics cover a broad range; they includeinvestigations of high brightness-temperature objects emitting non-thermal radiation, atomic andmolecular processes, synchrotron radiation and pulsar emission. The high sensitivity provided by See . VN: Present & Future
J. Anton Zensus the large collecting area of many of its elements makes the EVN especially suitable for the studyof faint objects such as young radio supernovae.
EVN in context
In its early days VLBI was confined to centimetre wavelengths where observingsystems made it feasible; shorter wavelengths suffered from short coherence times and relativelylow performance of receivers, and longer wavelengths were affected by the ionosphere and plaguedby steadily increasing radio frequency interference. Recent technical developments have expandedthe parameter space in radio astronomy. Progress in processing data from thousands of dipolesand “software telescopes” have pushed towards longer wavelengths, with pathfinders and precur-sors of the Square Kilometre Array (SKA), such as LOFAR. At the same time, improvementsin detector techniques and increasing bandwidths have triggered the advent of new-generation,short-wavelength telescopes, the recently dedicated Atacama Large Millimetre/sub-millimetre Ar-ray (ALMA) being the most important. It is planned that ALMA, as a phased array, will observeas an element in millimetre VLBI arrays, notably with the aim of investigating the morphologyof the immediate neighbourhood of the super-massive black holes at the Galactic Centre and inthe nearby galaxy M 87 – the so-called Event Horizon Telescope [14]. Additionally, the desirefor longer baselines has pushed VLBI to have elements in Earth orbit, first with the VSOP projectin the late 1990s [15] and currently RadioAstron [16]. EVN as a ground array is a key elementsupporting RadioAstron observations. The use of a large dish such as Effelsberg together withthe small dish onboard
Spektr-R has the same collecting area as two 30-m dishes. The first resultsreported are spectacular (see e.g., [17] in this conference).
Observing
The EVN performs observations with disk recording (standard EVN, three sessionsof three weeks each per year) or in real time (e-VLBI, 10 sessions per year, each of 24h). Out-of-session scheduling has been introduced recently in blocks of up to 12 hours of duration (upto a maximum of 144 hours per year), for specific purposes which justify observations outside ofregular sessions. Observations are possible at 92, 49, 30, 21, 18, 13, 6, 5, 3.6, 1.3, and 0.7 cm wave-length. Joint observations with the Very Long Baseline Array (VLBA), (’Global’ proposals) canalso include the Green Bank Telescope and the phased Jansky Very Large Array. Global proposalscan currently use up to 1 Gbps data bit rate. Joint observationswith the RadioAstron project arepossible as well. Following the Korean VLBI Network joining the EVN as an associate member in2014, it is planned that some joint time with the Australian Long Baseline Array will be available,starting in 2015, creating a real global array. The details and updates of the EVN performanceare announced in every call for proposals . The status of the telescopes, receiver availability, ob-serving modes, etc., is maintained by JIVE in the EVN status tables . For observations at 3.5 mm,astronomers can use the Global Millimetre VLBI Array (GMVA), operated jointly by the MPIfR,IRAM, Onsala and NRAO . As mentioned above the KVN recently joined the EVN. Its 3 antennas (with separa-tions up to 480 km) at the easternmost edge of the network enhance remarkably the ( u , v ) coverage. See . See . See . VN: Present & Future
J. Anton Zensus
An interesting feature of these telescopes is their novel high-frequency capabilities, since simulta-neous observations are possible at 13, 7, 3.5, and 2 mm wavelength; 13 and 7 mm are offered bythe EVN for joint observations.RadioAstron has performed joint observations with the EVN since early 2012, combining thehigh resolution provided by space VLBI with the high sensitivity of the EVN (see above).Recently a new correlator developed at JIVE (UniBoard project, supported by RadioNet3, see[18]) has successfully demonstrated 4 Gbps operation. When brought into operation the correlatorwill support 32 stations with 64 MHz bandwidth, integration times of 0.022 s to 1 s, and a frequencyresolution up to 15.625 kHz.In September 2014 the radome of the 20m-Onsala telescope was renewed. The top cap of 50panels was replaced in one piece, and the remaining 570 elements were changed one by one .As mentioned above the Tianma 65-m telescope will be available for EVN observations in2015. It will operate with adaptive optics in all the bands offered by the EVN from 21 cm to 7 mm.First fringes with the EVN were obtained in March 2014 [19]. It can also provide a very shortbaseline together with the Seshan 25-m telescope. EU Support
The EVN is an excellent example of international cooperation in science. Thiscollaborative aspect has been boosted over the last twenty years by the support of the EuropeanCommission via different funding instruments. Following from support inder the 3 rd FrameworkProgram (FP3) with The European VLBI network of radio telescopes , it continued in FP4 withEnhancing the European VLBI Network of Radio Telescopes and Access to the EVN of radiotelescopes , in FP5 with the projects EVN-ACCESS and FARADAY , in FP6 with RadioNet and EXPReS , and in FP7 with NEXPReS , RadioNet-FP7 and currently RadioNet3 .Additional funding for EVN research activities was provided by programs such as the coop-eration with the former Soviet Union by The nature and origin of the most compact cosmic radio See http://goo.gl/Ca0dJH . Ref. CHGE920011, programme FP3-HCM. Code FMGE980101, programme FP4-TMR. Code FMGE950012, programme FP4-TMR, subprogramme 0201 - Access for researchers, funding scheme 0201- Access for researchers. European vlbi network via the joint institute for vlbi in europe, Ref. HPRI-CT-1999-00045, programme FP5-HUMAN POTENTIAL. Focal-plane arrays for radio astronomy; design, access and yield, Ref. HPRI-CT-2001-50031, programme FP5-HUMAN POTENTIAL. RadioNet: AdvancedRadioAstronomyinEurope, Ref. 505818, programme FP6-INFRASTRUCTURES, subpro-gramme INFRASTR-2.1 - Integrating activities combining cooperation networks with transnational access and researchprojects. EXPReS:a production astronomye-VLBIinfrastructure, Ref. 026642, programme FP6-IST, funding scheme I3 -Research Infrastructure-Integrated Infrastructure Initiative. NEXPReS- Novel EXplorations Pushing Robust e-VLBI Services, Ref. 261525, programme FP7-INFRASTRUCTURES, subprogramme INFRA-2010-1.2.3 - Virtual Research Communities. Advanced Radio Astronomy in Europe, Ref. 227290, programme FP7-INFRASTRUCTURES, subprogrammeINFRA-2008-1.1.1 - Bottom-up approach: Integrating Activities in all scientific and technological fields. Advanced Radio Astronomy in Europe, Ref. 283393, programme FP7-INFRASTRUCTURES, subprogrammeINFRA-2011-1.1.21. - Research Infrastructures for advanced radio astronomy. VN: Present & Future
J. Anton Zensus sourcesknownintheUniverse , geodesy-related projects such as RADIO-INTERFEROMETRY ,and research training networks such as CERES , ANGLES and ESTRELA .The present I3 project RadioNet3 includes a transnational access programme (which supportsEVN observations and data analysis), networking activities (which, amongst other things, supportthis conference), and joint reseach activities to support research and development at the radio as-tronomical facilities in Europe, including JIVE and several EVN radio telescopes. A completedescription of the project and its goals is provided in its webpage . RadioNet3 also contributes tothe implementation of the strategic plan for European radio astronomy (AstroNet ) by building asustainable radio astronomical research community. Scientific
As reported above, the EVN has produced hundreds of scientific publications in severalareas; highlights are shown regularly on the EVN webpages. Its high fidelity imaging is especiallyuseful for global experiments and for observations of complex jet structures, e.g., in the study ofhelical features in 0836+710 [20]. Methanol masers can be probed at 5 cm wavelength, and theseastrometric results complement astrometric studies performed at 1 cm with water masers, see [21].The high sensitivity shows its full power in the study of ultraluminous X-ray sources [22], in settingupper limits to the emission from radio supernovae, e.g., SN 2014 [23], or in the imaging of theCrab nebula [24]. Synergies with observations from telescopes at the very highest frequencies arepossible, as in the case of the blazar IC 310 in the Perseus cluster, studied jointly by MAGIC andthe EVN [25].
3. The future
JIV-ERIC
The future has now become the present, since the European Commission decided inthe course of writing this contribution to allow JIVE to become a European Research InfrastructureConsortium, initially with four member countries (The Netherlands, United Kingdom, Sweden andFrance). In addition, research councils and institutes in other countries – Italy, Spain, South Africa,Germany and China – will contribute to JIVE as well. The official dedication of the JIV-ERIC isplanned for April 2015.
Expanding the network
Six dishes were recently added to the network (KVAZAR with 3 ×
32 min 2009 and KVN with 3 ×
21 m in 2014). The telescopes in Sardinia (64-m) and Tianma (65-m)are a reality and will increasingly participate in EVN observations in 2015. Further in the future Ref. INTAS-94-4010. Measurement of vertical crustal motion in Europe by VLBI, Ref. FMRX960071, programme FP4-TMR, subpro-gramme 1.4.1.-3.1S4 - Environment and Geosciences. The universe at high redshift and the physics of active galaxies from multi-wave length studies of compact ra-dio sources - consortium for European research on extragalactic surveys, Ref. FMRX960034, programme FP4-TMR,subprogramme 1.4.1.-3.1S7 - Physics. Astrophysics Network for Galaxy Lensing Studies, Ref. 505183, programme FP6-MOBILITY, subprogrammeMOBILITY-1.1 - Marie Curie Research Training Networks (RTN). Early stage training site for European long-wavelength Astronomy, Ref. 19669, programme FP6-MOBILITY,subprogramme MOBILITY-1.2 - Marie Curie Host Fellowships - Early stage research training (EST). See . See . VN: Present & Future
J. Anton Zensus are the planned 110-m telescope in Qitai, near Urumqi, and the FAST 500-m telescope in China,which could join EVN observations, and also a 70-m class telescope in Poland (RT90) to the northof Toru´n. Furthermore, a beam-formed MeerKAT telescope would be an excellent addition to thenetwork to the South, with a short baseline to Hartebeesthoek and with high sensitivity. Plans foran African VLBI array are also being developed, and this would yield an unprecendented coverageat centimetre wavelengths, to boost radio astronomy in the next years, complementing the SquareKilometre Array.
New frontiers
In the future the EVN will continue being a key instrument in radio astronomy,complementing multi-messenger campaigns, in the study of transients, enhancing its image fidelityand astrometric precision, complementing millimetre- and space-VLBI, and as a match in the radiofor astrometric measurements in the era of GAIA. Even when other facilities are threatened withfunding cuts, one of the strengths of the EVN is its international nature, making a sustainable andflexible facility for many years in the future.
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