4 PI SKY Studies Evolution of Tidal Disruption Event

The 4 PI SKY research group has been involved in the study of a rare transient phenomena, known as a tidal disruption event (TDE). A TDE is the result of a star straying too close to a supermassive black hole, and being ripped apart by its strong gravitational field. The remains of the star then fall down onto the black hole, and emit across the electromagnetic spectrum (see illustration).


Image credit: NASA/CXC/U. Michigan/J. Miller et al.; Illustration: NASA/CXC/M. Weiss

Members of the 4 PI SKY group have been continually observing radio emission from this source using the Arcminute Microkelvin Imager located in Cambridge, with observations spanning 3 years. Their research has indicated the possible presence of ultra-fast outflows emanating from the black hole, known as jets.

Further reading: https://arxiv.org/abs/1511.08803https://arxiv.org/abs/1801.03094


The MeerKAT core


This a photo of the MeerKAT core, taken on Oct 17 (2017) [credit Thomas Abbott, SKA South Africa]. All 64 MeerKAT primary antennas are now in place. In this picture 44 antennas are visible.

4 PI SKY co-leads the ThunderKAT Large Survey Programme (LSP) on MeerKAT, which has 1380 hours of guaranteed time during the MeerKAT survey phase (~2018-2023) as well as an agreement to search all other LSP data commensally to search for transients.


Exciting times ahead!

4 PI SKY involved in jets breakthrough

The 4 PI SKY research group was involved in a significant measurement of the size and associated timescales very close to the base of a black hole relativistic jet, in a project led by collaborators at The University of Southampton.

Picture of black hole jet

High time resolution X-ray and infrared observations during flares from the black hole V404 Cyg in 2015 revealed a ~0.1 sec time delay between the emission in the two bands. There are good arguments already that the infrared emission arises from the ‘base’ of the relativistic jet, and AMI-LA radio observations provided simultaneously by the 4 PI SKY group confirmed this. This allowed the team, led by Dr Poshak Gandhi from Southampton, to establish a size scale of ~0.1 light seconds between the X-ray emitting region (inner parts of the accretion flow) and the first synchrotron emitting zone (the jet base). The research is published in Nature Astronomy, and the article can be found on the arXiv as arXiv:1710.09838.

For the full Southampton press release (including movie!) go to:


4 PI SKY observe the radio counterpart to merging neutron stars

The recent detection of a neutron star-neutron star merger by aLIGO+VIRGO, combined with the associated electromagnetic counterpart have generated a huge amount of excitement in the astrophysical community.


The 4 PI SKY research group has been strongly involved in this, in particular in the radio regime. The JAGWAR project, which led to the discovery of the radio counterpart (arXiv:1710.05435), is led by Kunal Mooley, a member of 4 PI SKY. Kunal and Rob Fender were also involved in observations of the field with MeerKAT (still in commissioning) and Rob was also part of the effort to find a low frequency radio counterpart with LOFAR. Kunal and Rob are furthermore also involved in a project, GWAMI, to try and chase the radio counterparts to future GW events with AMI-LA.



4 Pi Sky VOEvent Broker becomes the standard for rapid-response triggering

Due to the success of the Arcminute Microkelvin Imager Large-Array Rapid-Response Mode (ALARRM) observing program, the 4 Pi Sky VOEvent Broker and the Comet VOEvent client are fast becoming the go-to software standard for receiving, parsing and filtering VOEvent transient alerts. These software allow for the full automation and timely follow-up of transient events using telescopes and facilities with rapid-response observing modes.

Recently the “Radio-Gamma-ray: Transient Alert Mechanisms” meeting was held in Amsterdam (26 – 28 September), in an effort to push for a standardisation of transient astronomy infrastructure and techniques, such as the generation, dissemination, distribution, and reaction to multi-messenger events.

At this meeting, several facilities including the Low Frequency Array (LOFAR), the Australia Telescope Compact Array (ATCA), and the High Energy Stereoscopic System (H.E.S.S) reported they were using Comet and the 4 Pi Sky VOEvent Broker to conduct rapid-response triggering on transient events. The International Virtual Observatory Alliance (IVOA), who manage and edit the VOEvent protocol, recognise both Comet and the 4 Pi Sky VOEvent tools as key software for implementing a VOEvent response network (see slide images below).


Experiments on the Australia Telescope Compact Array, led by Gemma Anderson, use the 4 Pi Sky VOEvent broker to trigger on Swift transient events


Stefan Ohm explains that H.E.S.S. triggers on ASASSN and GAIA transients using the 4 Pi Sky VOEvent broker


Dave Morris at the International Virtual Observatory Alliance (IVOA) mentions that Comet and the 4 Pi Sky VOEvent broker are key software for VOEvent triggering