Russians, Americans and Europeans work together to set records for celestial detail.
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May 08, 2012

Records were made this January when the RadioAstron satellite was joined by ground-based telescopes, forming a radio telescope 220,000 km across òÀÓ roughly 20 times larger than the Earth.

RadioAstron, a Russian orbital telescope of 10 meter diameter, joined with ground-based observatories to resolve objects 50 times smaller than is possible with the Hubble Space Telescope. As RadioAstron is only ten meters across, the participation of the worldòÀÙs largest radio telescope, Arecibo ObservatoryòÀÙs William E. Gordon Telescope, is particularly important.

Dr. Tapasi Ghosh, an astronomer at Arecibo Observatory, explained, òÀÜArecibo is critical in making this international endeavor succeed.ˆà With our 305-meter telescope we contribute the collecting area needed to compensate for the small size of RadioAstron, ensuring that sufficient radio waves are captured to make the experiment work.òÀÝ

On January 25th, 2012, the Arecibo telescope, together with those at Westerbork in the Netherlands and Effelsberg in Germany, helped RadioAstron to detect its first signals at 92-cm wavelength. Astronomers combined the signals from the individual antennas to form the equivalent of a huge single telescope, using a technique called Very Long Baseline Interferometry (VLBI). At the time, the spacecraft was at its furthest possible distance from the Earth, providing a baseline of 20 Earth diameters in length.

Dr. Chris Salter, also of Arecibo Observatory, said, òÀÜThis represents a major step forward for radio astronomy.ˆà It is the first time weòÀÙve been able to form a telescope with baselines this long òÀÓ with the power this gives us, we could stand in Miami and see a quarter in Seattle.òÀÝ

The target for the record-breaking observation was the pulsar B0950+08, a rotating neutron star 900 light years from the Earth.ˆà The all-important òÀÜinterference fringesòÀÝ òÀÓ the sign that the telescopes have been successfully joined òÀÓ were seen between the RadioAstron satellite and all three of the ground-based telescopes.ˆà

Pulse-to-pulse variations are seen in the pulsar signal due to irregularities in the interstellar plasma, similar to the twinkling of stars caused by the EarthòÀÙs atmosphere.ˆà These are only seen when looking at very compact objects such as pulsars. Consequently, these observations provide astronomers with a tool to study both the interstellar medium and the pulsar itself.ˆà With the amazing resolution of RadioAstron, it is even possible to see where on the neutron star the signal is coming from, telling us more about how these enigmatic objects work.

This experiment both confirms RadioAstron's capabilities and provides the dish's first important scientific data at 92-cm wavelength. The ten brightest radio pulsars seen from the Earth will be studied in the RadioAstron early science program.ˆà RadioAstorn will also be studying other compact objects, such as quasars and molecular maser emissions from regions of star formation.

Images:

The RadioAstron spaceantenna observes a celestial radio source simultaneously with ground-based dishes. The signals are subsequently combined interferometrically to recover the image that would be obtained by a telescope having a diameter of the spacecraft's orbit.
(Image from http://www.federalspace.ru/img/site/d148_3.jpg)

The RadioAstron orbital antenna (10-meter diameter); the Arecibo William E. Gordon Telescope (305-m diameter); the Westerbork Synthesis Radio Telescope (14 †× 25-m diameter antennas), and the Effelsberg dish (100-m diameter). (Images fromˆà http://asc-lebedev.ru, www.naic.edu, www.nentjes.info/Kijkers/telescopes-a.htm,ˆà and credit: N. Tacken, MPIfR)

Profiles of a single pulse from the pulsar B0950+08 detected individually(in red) by the three ground telescopes and RadioAstron. The inset presents the interferometer signal between RadioAstron and Arecibo for this single pulse.ˆà (Image credit:Yuri Kovalev, Lebedev Physical Inst.)

Fig: The interferometer signals between RadioAstron and Arecibo for the pulsar B0950+08 for the full one hour long session. On the axes: time (sec), interferometric delay (sec), and the interferometer signal in color.ˆà The signal variations in time are due to interstellar scintillations of the pulsar emission. (Image credit: Yuri Kovalev,ˆà Lebedev Physical Inst.)

The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968), and in alliance with Ana G. M†éndez-Universidad Metropolitana, and the Universities Space Research Association.

The opinions expressed in this article are those of the author, and they do not necessarily reflect those of the Arecibo Observatory, SRI International, or the National Science Foundation.

For more information please contact authors
Dr. Tapasi Ghosh [tghosh@naic,edu, (787) 878-2612 ext. 289] or Dr. Chris Salter [csalter@naic.edu, (787) 878-2612 ext. 281].