DWINGELOO, The Netherlands (2 March 2011) - Using a perfectly orchestrated world-wide network of radio telescopes, astronomers have produced a high-resolution map of an Active Galactic Nucleus (AGN) belonging to an unknown class of gamma-ray sources. The unusual source and the groundbreaking technique used to produce the image are detailed in a letter published today in Astronomy & Astrophysics.
The paper, "Global e-VLBI observations of the gamma-ray narrow line Seyfert 1 PMN J0948+0022" (abstract, full html, PDF), presents very high resolution radio observations of the active nucleus of a peculiar Seyfert galaxy. In 2009, observations made with the Fermi satellite of PMN J0948+0022 revealed the emission of high energy gamma rays, presumably from the active nucleus of this galaxy. No other galaxy of this kind had ever been revealed at such high energy, and it could be the first member of a new class of gamma-ray extragalactic sources. Gamma-ray emission is typically associated with relativistic jets of plasma that also emit radio waves. Therefore, the best way to image such structure is in the radio spectrum using VLBI, Very Long Baseline Interferometry. "We immediately realized this was an extremely interesting object, so we decided to look at it using the best resolution we could attain. And we knew it was important to do it as soon as possible, since this was a variable source," says Marcello Giroletti, astronomer at INAF-IRA in Bologna, Italy, who led the observations.
VLBI observations are performed by simultaneously pointing at a source with telescopes distributed across several countries, and the more distant their locations, the better the achieved angular resolution. With traditional VLBI, each station records data on hard disks which are shipped to a central supercomputer called a correlator, which processes the data. Recently, it has become possible to directly connect the telescopes to the correlator using optical fibres and to process the data in real-time, in the so-called electronic VLBI (e-VLBI) technique, providing astronomers with data in a matter of hours rather than weeks. Although e-VLBI is done routinely at the European scale, it had only been done at a global scale for testing and demonstration purposes. Scientific observations using a world-scale, real-time connected array had never been done before.
Giroletti and his team conducted observations in three sessions from May to July 2009 using radio telescopes in Europe, East Asia, and Australia, connecting observatories as far apart as 12,458 km. With such a long baseline, the central region of the galaxy was mapped at an astonishing resolution of a few tens of microarcseconds - about the same as identifying a football on the moon!
All aspects of the technical experiment were successful, with each telescope streaming its data to the correlator at the Joint Institute for VLBI in Europe (JIVE) in the Netherlands. This type of observation is testing new frontiers, since it permits real-time network performance monitoring and the possibility of delivering prompt results, which is essential for coordination with other observatories at other wavelengths. Several of them, including space satellites Fermi and Swift, joined the same observing campaign. More radio telescopes are expected to become connected through real-time high-speed networks, such as the upcoming 64m INAF Sardinia Radio Telescope, and technology developments are being made through the NEXPReS project to remove the distinction between traditional VLBI and e-VLBI techniques.
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The Joint Institute for VLBI in Europe (JIVE, www.jive.nl) is a scientific foundation with a mandate to support the operations of the European VLBI Network (EVN). For this purpose it maintains, operates and develops the MKIV EVN Data Processor, a powerful supercomputer that combines the signals from radio telescopes located across the planet. Through this technique, called Very Long Baseline Interferometry (VLBI), astronomers can make detailed images of cosmic radio sources, providing astronomers with the clearest, highest resolution view of some of the most distant and energetic objects in the Universe.
INAF (www.inaf.it) is the Italian National Astrophysics Institute, which operates all Astronomy and Astrophysics Research Institutes in the country. Founded in 1999, it is a relatively young institute with deep historic roots in Italian astronomy, of which Galileo Galilei is the best example. Italian astronomy flourished in the second half of the 20th century, and INAF has a strong representation on the international astronomical stage. INAF collaborates with many international facilities, such as the European Southern Observatory telescopes, the Large Binocular Telescope and the European VLBI Network.
Novel Explorations Pushing Robust e VLBI Services (NEXPReS, www.nexpres.eu) is a three-year project with the goal of implementing real-time, electronic VLBI (e-VLBI) into all observations conducted by the European VLBI Network. This will be achieved through development of a variety of technologies including: cloud correlation; high-bandwidth on demand; distributed correlation; and high-bandwidth, high-capacity networked storage on demand. NEXPReS is comprised of 15 partner institutes in eleven countries and is coordinated by JIVE. NEXPReS in an e‑Infrastructure project funded by the European Union's Seventh Framework Programme under Grant Agreement RI‑261525.
Marcello Giroletti, Researcher
INAF, Institute of Radioastronomy
+39 051 639 9394
giroletti [at] ira [dot] inaf [dot] it
Zsolt Paragi, Senior Support Scientist
Joint Institute for VLBI in Europe
+31 (0)521 596536
paragi [at] jive [dot] nl
Click on a thumbnail below to view full-sized image.
Map of telescopes that participated in observations of PMN J0948+0022
Data throughput from 23 May 2009 e-VLBI observation to correlator at JIVE
Data throughput from 10 June 2009 e-VLBI observation to correlator at JIVE
Data throughput from 4 July 2009 e-VLBI observation to correlator at JIVE
Click here to view an interview (Italian) with lead author Marcello Giroletti.