4 PI SKY ON THE OPTICAL COUNTERPARTS OF RADIO TRANSIENTS

4 Pi Sky has today published a study of the optical and radio flux density properties of a wide range of astrophysical transient phenomena – from Galactic flare stars to extragalactic gamma-ray bursts (GRBs). The aim of the investigation was to answer the question of whether a radio transient source could be classified from an optical flux density measurement obtained through swift follow-up. In fact, this scenario may suddenly become very frequent with the recent inauguration of MeerLICHT, a robotic optical telescope that will track the new radio telescope MeerKAT, providing optical photometric coverage of any night-time radio transients discovered by MeerKAT!

By analysing approximately 12,000 pairs of radio and optical flux density measurements, we found that there was a clear separation in the parameter space of Galactic and extragalactic objects, as seen in Figure 1 from the publication reproduced below. We also saw that objects from specific populations generally clustered together as evidenced by the distribution of supernovae (SNe) and GRBs.

fig01

Figure 1 from the publication that shows the optical and radio flux densities of different transient phenomena plotted against one another. It shows how the majority of Galactic and extragalactic sources, such as stars and quasars respectively, are well separated.

The measurements included in the plot above are recorded at a single time, but the flux density of transients change significantly as they evolve. We explored how this would appear in the radio and optical parameter space by including a dynamic data sample that followed the radio and optical evolution over months or even years. Below is a plot showing a result of that study, specifically for SNe. It shows that many events follow a similar anti-clockwise trajectory, a feature that could help in classifying an object if an initial classification is unclear. In the paper we also explore how GRBs, X-ray binaries, cataclysmic variable and quasars evolve over time.

fig06c

The evolution of a selection of supernova events in radio and optical flux density over time. The green and red circles signify the beginning and end of the measurements for the respective object, where as the numbers denote the time in days after the explosion date of the event.

The study is the first step in using the radio and optical flux density information of a transient as part of a classification pipeline – and will already provide a very useful reference for the MeerKAT/MeerLICHT project. As more simultaneous radio and optical data is collected thanks to projects such as that one, our understanding of the radio-optical transient sky will substantially improve and, importantly, allow us to ‘fill-in’ areas of the plot to see how populations appear beyond our current sensitivity limits.

The full paper can be found on arXiv here: https://arxiv.org/abs/1806.09815.

AMI-LA Transients: a new collaboration

On June 12, members of a new collaboration visited the AMI telescopes in Cambridge. A team led by Assaf Horesh, of the Hebrew University, Jerusalem, will work together with 4 PI SKY and Cambridge to perform a systematic study of radio supernovae with AMI-LA. We will also work together on the radio follow-up of Tidal Disruption Events.

AMIphotoHere are members of the teams from Cambridge, Oxford and Jerusalem in front of the telescopes of the AMI Large Array. Typical English weather, but the telescopes working fine, observing targets for the 4 PI SKY transients programme as we stood there. From left to right: Patrick Elwood, Assaf Horesh, Richard Saunders, Rob Fender, Joe Bright, Sara Motta, Itai Sfaradi, Paul Scott.

Small_arrayThe teams in the AMI Small Array enclosure. AMI-SA was performing an extensive AGN monitoring programme at the time.

MeerLICHT telescope inaugurated!

On May 25, Africa Day 2018, the MeerLICHT optical telescope was officially inaugurated at South Africa’s Sutherland observatory. Oxford, via the 4 pi sky project, is a key founding member of MeerLICHT.

The unique aspect of this telescope is that it will robotically track, all the time, where the MeerKAT radio telescope (expected to be itself inaugurated in the near future, and to commence full time survey operations by 2019) is pointing. The key science goals are astrophysical transients: if a radio transient is observed with MeerKAT, there will be simultaneous optical data (at night!) and vice versa. This is a very exciting and new exploration of parameter space.

ML_launch

Left to right: Patrick Woudt (UCT), Steven van Straten and Paul Groot (Radboud), Rudy Wijnands (Amsterdam), Dave Buckley (SAAO), Ben Stappers (Manchester), Rob Fender (Oxford and UCT)

Below is one of several first-light images released. This one is of Baade’s window, in the direction of the galactic centre, and this single image contains an estimated two millions stars.

mlicht-baade

There was a lot of press interest in the inauguration, and we even made the national tv:

Rob Fender MeerLICHT TV interview

The official Oxford press release is here:

Oxford press release

For more information see the MeerLICHT website at

MeerLICHT official web site

 

 

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).

14li_artist_impression

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

OLYMPUS DIGITAL CAMERA

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.

http://www.thunderkat.uct.ac.za/

Exciting times ahead!