Dawn of Radio Astronomy with Very Long Baseline Interferometry in Thailand

First Detection of VLBI Signals across 8500 km Baseline between TNRT and Effelsberg Radio Telescopes

The National Astronomical Research Institute of Thailand (NARIT: Public Organization), in collaboration with Max Planck Institute for Radio astronomy (MPIfR), has achieved the historic first detection of astronomical radio signals using Very Long Baseline Interferometry (VLBI)¹ with the 40-m Thai National Radio Telescope (TNRT). The experiment, which was supported by the Effelsberg 100-m radio telescope in Germany, marks the first ever VLBI signal detection made in Thailand.

pr20240531 1 01 Figure 1. The two radio telescopes used in this VLBI experiment: Right, the 40-m TNRT (photo credit: TNRT/NARIT) and left, the Effelsberg 100-m (photo credit: Norbert Tacken, MPIfR). The two radio telescopes are separated by a distance of 8,500 km and when combined they have the resolution of single 8,500 km-wide dish.

Very Long Baseline Interferometry is an extremely challenging observing mode in which the signals recorded by each telescope must be precisely aligned and added together. Doing this successfully combines the two telescopes into one giant virtual telescope with a resolving power (ability to see extremely small things far away) that is many thousands of times better than that of the individual telescopes.

The successful VLBI observations with the TNRT and the Effelsberg radio telescopes were conducted in the 1.658-1.674 GHz frequency range on May 16, 2024, UTC 14:00-17:00. The distance between these telescopes is approximately 8,500 km, resulting in a 4.4 milliarcsecond resolution, more than 13,000 times better than the human eye. If the human eye was capable of such a resolution, you would be able to see the centre circle of a football pitch on the moon.

During the experiment, the team observed four extra-galactic radio galaxies and quasars: OJ287, 3C273, M87 (Virgo A) and J2005+7752, which are bright continuum astronomical objects in radio wavelengths. The observation data were recorded in a cutting edge digital processing and recording system: the Effelsberg Direct Digitization (EDD) system, which is part of the Universal Software Backend (USB)² developed by MPIfR. All the members of the team that made this achievement possible are listed at the end of this release.

Through electronic data transfer from Thai National Radio Astronomy Observatory (TNRO)³ to MPIfR and signal processing to achieve an aperture synthesis with a VLBI data correlator at MPIfR, the team finally achieved detections of VLBI radio correlated signals (so-called “fringes”) in all the observed objects. The detected signals presented correlated amplitudes with signal-to-noise ratios that are equivalent to our expectations.

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Figure 2. VLBI fringe for the first time in Thailand detected together with the Effelsberg 100-m towards: (upper) fringe signal detected in OJ287, which is the brightest source in this experiment, as 3-dimensional plot with delay⁴, delay rate, and amplitude axes. (mid and lower) fringe signals as 2-dimensional plots detected in, (mid-left) J2005+7752, (mid-right) OJ287, (lower-left) M87, and (lower-right) 3C273.

Dr. Gundolf Wieching, Division Head of Electronic Department in MPIfR, states “It has been an honour to follow the journey of the excellent NARIT team to the first VLBI observations in Thailand. This is a significant milestone, only possible with the great NARIT team, and shows the potential of the superb TNRT telescope for future science.”.

Dr. Koichiro Sugiyama, Chief Scientist of TNRO in NARIT, states “We are really honoured to welcome this historical moment of the 1^st VLBI signal detection of the 40-m TNRT together with excellent team of MPIfR. This is the dawn of radio astronomy with VLBI technique in Thailand. Based on this great successful, we look forward to accelerate and strengthen research collaboration with the world-wide radio astronomy community through VLBI observations.”.

This successful experiment is the essential first step towards expanding research fields and opportunities with the 40-m TNRT through world-wide collaboration with VLBI networks, such as the European VLBI Network, Very Long Baseline Array, East Asia VLBI Network, Australian Long Baseline Array, Asia Pacific Telescope, Global VLBI Array, and many more. This also provides a solid foundation to establish a national VLBI array in Thailand, the so-called TVA, and a next regional VLBI network in South-East Asia, so-celled SEAVN in collaboration with Indonesia, Malaysia, Vietnam, etc. in the near future.

These achievements are the result of a long-term collaboration between NARIT and MPIfR since 2012, leading to an agreement in 2018 for the development of state-of-the-art L- and K-band receivers with direct digitisation and the development of a generic astronomical software backend for TNRT.

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Figure 3. GP photo took during the operation at each site through contacting online, and (lower)

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Figure 4. All the members of this task force. Left 2 lines show MPIfR team (from upper to lower, Gundolf Wieching, Ewan Barr, Niclas Esser, Uwe Bach, Jan Wagner, Jason Wu, and Jompoj Wongphechauxsorn) and right 3 lines show NARIT team (Koichiro Sugiyama, Spiro Sarris, Teep Chairin Nobuyuki Sakai, Naphat Yawilerng, Nikom Prasert, Prachayapan Jiraya, Pathit Chatuphot, and Haseng Sani), respectively.

Members of a task force achieving this VLBI first signal detection are below:

MPIfR: Gundolf Wieching, Ewan Barr, Niclas Esser, Uwe Bach, Jan Wagner, Jason Wu, Jompoj Wongphechauxsorn, et al.

NARIT: Koichiro Sugiyama, Spiro Sarris, Teep Chairin Nobuyuki Sakai, Naphat Yawilerng, Nikom Prasert, Prachayapan Jiraya, Pathit Chatuphot, Haseng Sani, et al.

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Figure 5. Upper - The signing of the MoU between NARIT and MPIfR in 2012, (from left to right) Assoc. Prof. Boonrucksar Soonthornthum, Founding Director of NARIT; Prof. Karl Menten, Managing Director of MPIfR and Director of the Research Department Millimeter and Submillimeter Astronomy; Prof. Michael Kramer, Director of the Research Department Fundamental Physics in Radio Astronomy. Lower - The 2018 Annex Signing Ceremony, (from left to right) Dr. Ewan Barr, Group Leader Electronics, Software Development; Dr. Gundolf Wieching, Division Head of Electronic Department; Prof. Michael Kramer; Prof. Anton Zensus, Managing Director and Director of the Research Department Radio Astronomy/VLBI; Dr. Saran Poshyachinda, Executive Director of NARIT; Dr. Suvit Maesincee, Minister of Science and Technology of Thailand; Dr. Manop Sittidech, Minister Counsellor (Science and Technology).