The universe is teeming with objects that exhibit drastic variations in brightness over time scale from milliseconds to years. These are known as transients and include events such as Fast Radio Bursts (FRBs), X-ray binary systems (XRBs), soft gamma repeaters (SGRs), gamma ray bursts (GRBs), supernovae (SNe) and more. Most of these transients are associated with ejections of matter, in some cases at (ultra)relativistic speeds that can produce radiation at radio frequencies.
Fast Radio Bursts
Some theories suggest that a FRB originate in the collapse of a particularly massive star to a hyper-magnetised neutron star. Other theories propose that the radio bursts come from the jet formed by a massive black hole.
Most of the observed bursts do not repeat, but some do which has led astronomers to consider whether there are multiple types of FRBs. At ASTRON, we use the APERTIF system on the WSRT to search for new sources of repeating FRBs that can shed light on the mysterious origin(s) of these cosmic signals.
Imaging Searches for transients
Astronomers at ASTRON work in collaboration with teams conducting widefield surveys on LOFAR and MeerKAT to look for a wide range of variable radio sources and find new and previously unknown radio transient phenomena. The transient team at ASTRON has also developed the LOFAR Transient Pipeline as part of the AARTFAAC project. AARTFAAC uses LOFAR to scan the whole visible radio sky every second in search of extreme transients such as black holes and neutron stars.
Follow-up of multi-messenger transients
Many known transient and variable sources have detectable emission at radio frequencies. Using facilities such as LOFAR, we conduct dedicated follow-up observations of newly detected transient sources by other multi-messenger facilities (e.g. Advanced LIGO and the Swift Satellite). These sources have recently included Gravitational Wave Events (compact binary mergers) and GRBs. Follow-up is conducted on two key timescales: rapid response, where the telescope automatically observes a transient with no human interaction, and late time observations to monitor the source. To implement the LOFAR rapid response mode, we collaborated closely with the ASTERICS team at ASTRON.
Joeri van Leeuwen
Sander ter Veen