Note: This is the literal proposal as sent on December 16, 2012 to the coordinators of the NWO/NRF collaboration, prof. Wijers and Kraan-Korteweg. Because of an unclear agreement on the actual submission to NWO/NRF this proposal is only now formally submitted to both agencies. The working group on Astrophysical transients, their hosts and their physics,established under the NWO/NRF bilateral agreement in Astronomy and enabling technologies for Astronomy, has a natural focus on the approved two large radio transient surveys defined on the SKA-precursor telescope MeerKAT (TRAPUM and ThunderKAT) and the closely associated LOFAR transient key science project (TKP) on LOFAR2. Preparatory work on these large surveys and their associated science programs are currently ongoing at a number of Dutch and South African research institutes and universities, in close collaboration with the Universities of Southampton and Manchester in the UK. These projects have already established close ties between a number of institutes in the Netherlands and South Africa, both in terms of research visits of senior staff and joint co-supervision of South African postgraduate students. The latter is best illustrated by the current Erasmus Mundus SAPIENT exchange between the University of Cape Town (UCT) and Radboud University Nijmegen (RU) of two South African PhD students. It is on this strong foundation that this working group seeks to strengthen existing research collaborations and identify growing areas of common research interest in astrophysical transients and their hosts by bringing together researchers in South Africa and the Netherlands through a research exchange program involving staff, postdocs and postgraduate students, and joint workshops. As transient astronomy is multi-wavelength and multi-messenger astronomy, this working group automatically includes efforts both at radio, optical, X-rays wavelengths as well as astroparticle physics. Within this context, the working group identifies the concept of a small optical telescope (MeerLICHT) with an instantaneous field-of-view identical to MeerKAT and permanently linked in real-time to MeerKAT, as a novel and innovative approach to transient science, maximising the scientific returns of the fully commensal observing mode of MeerKAT as employed by ThunderKAT and TRAPUM. We also identify a need for high-energy coverage, in particular from space. Given the membership of RU in Virgo, the North-West University (NWU) participation, and a University of Amsterdam (UvA)/RU-led proposal for participation in the Cerenkov Telescope Array (CTA), it is natural to include multi-messenger astronomy within this working group, as the source populations of transients are also the natural source populations of TeV photons and gravitational waves.

Following the Memorandum OF Understanding between the CHINA NATIONAL SPACE ADMINISTRATION (CNSA) and the NETHERLANDS SPACE OFFICE (NSO) concerning the cooperation on the Chang’E-4 mission, the Netherlands-China Low frequency Explorer (NCLE) payload is currently being developed by the joint Sino-Dutch teams. NCLE is regarded as a pathfinder mission for a future space-based low-frequency radio interferometer which aims at investigating the evolution and formation of the structures in the Dark Ages and Cosmic Dawn. Here we propose for two PhD positions to prepare for and to execute the science exploitation of the NCLE payload. The PhDs will become part of the NCLE team, collaborating with both scientist and engineers on the Dutch and Chinese side. We propose that in phase I of the project the PhDs take part in the commissioning of the NCLE instrument, while one PhD has the focus on the calibration of the instrument and the other focusses more on the design, implementation and calibration of the data pipeline. In phase II we identify constraining the 21-cm line emission global Dark Ages and Cosmic Dawn signal as the major science case, while the study of the emission from the Sun and the large planets is considered science that can easily be addressed by NCLE during the 4 year PhD tracks. In addition, a number of ancillary science cases are identified, ranging from the production of a low-frequency radio sky map to the study of the Lunar ionosphere. Finally, in collaboration with technical teams at the Chinese and Dutch side, we propose that an important outcome of the 2 PhD tracks will be a future concept for a space-based low-frequency radio facility. The work proposed here supports this unique Sino-Dutch project and helps preparing for the science exploitation of NCLE well in time for the launch in May 2018.

When observed at radio wavelengths, the sky looks very different from the familiar optical wavelength sky. It is full of extremely energetic phenomena such as: jets of radiation associated with black holes; particle acceleration during energetic collisions of the most massive objects in the Universe; and even interactions between nearby stars and the orbiting exoplanets. In this project we are mapping the radio wavelength sky and allowing us to view our energetic Universe in unprecedented detail.

The Low Frequency Array (LOFAR) is the world’s largest and most sensitive low frequency radio telescope with unprecedented spectral coverage (10-250 MHz) and resolution. After initial processing, the astronomical data are sent to the LOFAR long-term archive (LTA, currently hosting about 54 PB of data) for distribution to the Worldwide community. The LOFAR Data Valorization (LDV) project will apply innovative reduction routines to the data hosted at SURF, making LOFAR more accessible to users, increasing its science output, and reducing the data volume.

A unique feature of the LOFAR radio telescope, we developed, is the ability to catch ultra-short radio flashes with its new transient buffer boards. Ultra-short radio flashes represent a largely uncharted territory and can have widely different origins: from cosmic particles hitting our atmosphere to radio emission produced by neutron stars collapsing to a black hole. Here, we use this technique to investigate two of the most fascinating questions in high-energy astrophysics: the nature of cosmic rays and the origin of fast radio bursts. Cosmic rays are particles accelerated in cosmic sources to energies far exceeding anything achievable in particle accelerators, such as the LHC. Nature and origin of high-energy cosmic rays are still unknown. Using LOFAR we can now measure and decode radio flashes from cosmic rays, hitting the earth atmosphere in great detail, tentatively revealing a mix of Galactic iron and extragalactic hydrogen nuclei at 1017-1018 eV. Improving our measurements by an order of magnitude, we want to do the first high-precision composition measurement of cosmic rays in this energy range and clarify where cosmic rays are accelerated and what they are made of. Moreover, fast radio bursts have recently been discovered by high-frequency radio telescopes, which pose a complete mystery. The bursts might be due to cataclysmic explosions in the early universe, stars in our Milky Way, or something even closer to home. By adapting our cosmic-ray mode, fast radio bursts could be caught in the act, thereby allowing LOFAR to solve the riddle of their origin.