 Thank you very much for the kind introduction and yes good morning good afternoon and good evening to people who might be listening so I'm going to speak today about the extreme universe which is of course you know the main theme of this series of CTA talks it is essentially the focus of these ground based Cherenkov telescope so I'm going to talk about the extreme universe as viewed from the viewpoint of someone who uses radio telescopes to study the same kind of objects which are the targets for the Cherenkov telescope array and other related arrays that is the most extreme astrophysics so exploding stars accretion events around black holes relativistic jets all the same kinds of objects but observed in the radio bands rather than in Cherenkov light from high energy gamma rays and particles. So the talks going to be in six parts so in the first part I'm just going to give an introduction to the transient radio universe. And you can essentially divide as you'll see in a moment you can divide radio transients into two different flavors I'll talk you through the briefly the physics behind those. And I'll say a little bit about what our observations of with radio telescope can tell us about the physics of these extreme events sometimes in unique ways which really can't be probed in other ways. Later on in the talk, I'm going to talk about a number of specific projects which I'm involved in some which are broader some which are a little bit more narrow, which I hope you'll find interesting and which you you know I hope you'll see are relevant to the kind of projects that the Cherenkov telescope array will be interested in. I'll wrap up the talk by talking about the prospects for for future radio telescope arrays as we move through a very exciting era from the current very powerful and still relatively new radio arrays to things like the square kilometer array which will be here on the time scale of five to 10 years. Okay, so the introduction part one of six the transient radio universe. There are two types of essentially of radio transients, and the first type and the one which I study primarily myself are synchrotron transient so these are. This is a synchrotron radio emission from relativistic electron spiraling round magnetic fields as I'm sure you know, so it's an incoherent process. It's associated with particle acceleration and kinetic feedback so essentially in every case where you have something that's very active or very fast moving flow in astrophysics that's transferring a lot of energy to the rent to the local environment. It's moving much much greater than the local sound speed, and so you get shocks and you get particle acceleration, and we've known this for a long time we've seen this for a long time. In most cases and a lot of cases this is really a unique way to actually trying to measure the kinetic energy which was associated with this extreme astrophysical event. There are all sorts of very exciting and interesting physics with observations other wavelengths, for example, x-ray wavelength will tell you about the temperature of the hottest material optical spectroscopy can tell you about the elemental abundances, but in many cases it's really only the radio observations from the shocked ejected material, which can tell you about the kinetic feedback. And I'll show you two very different astrophysical sources. So this is a range of scales from almost the smallest before we had EHT further and this is for, this is for the active galactic nucleus M87 stepping up in scales to the very largest scales, and all of the radio emission you see from the relativistic jet in this sequence of images this is synchrotron emission produced by shock accelerated electrons probably certainly producing synchrotron radiation from relativistic electrons spiraling magnetic fields. What you see in the figure on the top right here is something quite different. This is a supernova remnant produced by a massive star which exploded some thousands of years ago, and yet the radio emission in this image also this is radio synchrotron emission produced in exactly the same way, except that the detailed physics of how the kinetic energy from the event was transferred to the local environment can vary in the case of jets. It's more collimated, perhaps in the case of most supernovae it's more isotropic. So the originator physics if you like of the event is different, but the physics, which leads to the fact we see the radio emission is very similar. So using a unique path to estimating the kinetic energy associated with these events, radio telescopes, radio telescope arrays, I should say interferometric arrays. They offer a unique combination of things which you can't really do with any other single instrument, unless it is a interferometer array, which is that they can offer very wide fields of view. Particularly in the modern era this is because we're using relatively small radio dishes, the smaller the dish the wider the field of view or what we call the primary beam. But when combined together in an array with long baselines between individual elements, they can also also offer very high angular resolution and that's usually that's really unique characteristic of interferometric array. So it's worth making a point that in terms of general transient surveys for most classes of object they still effectively less sensitive than optical or x-ray telescopes okay so what that means in practice is that, while they are fantastic diagnostics of the kinetic feedback and these usually most astrophysical transients will be discovered first as a result of optical or x-ray surveys and of course we are also in an era of incredible optical survey such as this wiki transients the facility and very soon we will have the the LSS to LSS T Rubin observatory producing lots of optical transients. The other type of radio transient which I won't dwell on much in this talk are coherent transient so this is essentially transients which seem to operate by something like the pulsar emission mechanism or some highly tuned an extreme version of that. Fast radio bursts are the the obvious examples of this, these are very short durations and have very very high brightness temperatures, we can see fast radio bursts at significant red shifts, which is extraordinary really because we think that these fast radio bursts originate from things you know, essentially neutron star magnetosphere so things perhaps you know very very small compared to for example a super massive black hole. The details of the underlying physics is very unclear, it's very exciting and very interesting to study, but the intrinsic pulse narrowness means that we can actually use these fast radio bursts to study the intervening intergalactic and interstellar medium. So here's an example here this was the first ever discovered fast radio burst the so called Lorimer burst. This was a very narrow burst of just a few milliseconds, but what you could see is that is you went to lower frequencies. So that's going downwards on the y axis, we see the pulse which are the the dark bits here arrived at later and later times in this kind of quadratic delay tells us that we're measuring dispersion in the cold interstellar medium. Radio telescopes are currently the only way to discover the sources of this is different to the synchrotron sounds that I just talked about these are really essentially being discovered in large numbers now by facilities such as chime just at radio wavelengths. Now if I tried to put this all into into a sort of a plane or context for all of radio transients one of the best ways of doing that is is using a version of this figure. So essentially what you're looking at here is on an x axis you're looking at timescale timescale of variability and on the y axis you're looking at radio luminosity. Okay, now there's an approximate dividing line here at 10 to the zero gigahertz second so which you can think of as a timescale of about one second on timescales longer than this we typically find and study our radio sources in sequences of images and that's the same with most of my studies and a much shorter timescales going down in fact sometimes as short as nanoseconds, a different operating mode is used, which is essentially called a beam formed model for those of you are not an expert you can think of this as the mode which is used to study pulsars. In the high time resolution regime there are all the standard pulsars there are some very short pulses observed from some, but importantly on the same timescales but a much higher luminosities are the mysterious fast radio bursts and of course there are, there are many there are hundreds more fast radio bursts which could be added to the plot now since China. So here in synchrotron sources live in this space over here this blue shaded region, and the reason for that is that synchrotron emission is limited to a certain brightness temperature of 10 to 12 Kelvin. And we find a whole range of objects from flares stars and brown dwarfs to supernovae to to know v containing white dwarfs x-ray binaries containing black holes and neutron stars, all the way up to to blaze ours associated with supermassive black holes. These are the most luminous objects and they also appear, often to have slightly higher brightness temperatures, that is their surface brightness appears to be a little bit higher than it should be able to be excuse me for synchrotron emission, and that's because they're relativistically beam towards us in many cases, as are some of the GRBs. So I'm going to mainly be focusing on the image plane synchrotron transient so that was an overview of the kind of the field of background of radio transients. So the first of the sub projects that I want to tell you about is Thundercat. Thundercat is a large survey program which myself and Patrick Vaught at the University of Cape Town we co-lead, and this is an image plane transient survey using the Meerkat radio telescope. So Meerkat is a radio telescope which was inaugurated in the northern Cape of South Africa, just over three years ago, and is extraordinarily sensitive and will become over a timescale of about five years will segue will morph into the first stage of the mid frequency component of the square kilometer array. So one of the main one of the main and most successful components of the Thundercat survey is to study X-ray binary systems. So X-ray binary systems are binary systems in which there is a relativistic accreting object, which is a creating matter from a companion star. So if I zoom in on this artist's impression here of an X-ray binary sort of as viewed from the viewpoint of the companion star then you have matter which is overflowing through the inner Lagrangian point. It flows down and it produces an accretion disk around the central object neutron star or black hole. Because the size scales of the inner accretion disk are very small and there's a lot of energy released there the temperatures are X-rays, hence these objects are called X-ray binaries. But the black holes and neutron stars in these objects we now know they produce very powerful relativistic jets, just like the supermassive black holes. And these are sites of some of the most extreme astrophysical processes within our own galaxy, and these we can study in the radio band. It's estimated there are around 10 to the 8 so it's 100 million stellar mass black holes in our own galaxy and maybe 0.01% of these are in binary systems they're really the tip of the iceberg. So what you're seeing here this is a this is a projection of our galaxy as observed with neocat as part of our Thundercat monitoring program. And first you'll note that there is the date which is changing in the lower left hand panel here so this is about two and a half years of radio monitoring of the sky. And actually what we do is whenever we get an indication from other surveys that something is perhaps X-ray bright, and we start monitoring it in the radio band and we do regular monitoring for a long time. So those of you who've worked in the past on x-rays would have seen movies like this for monitoring the x-ray sky, but this is the first time that we've been able to produce such a movie for the radio sky. All of these sources are within our own galaxy and every time you see one of these sources appear or brighten, this means that a stellar mass black hole or perhaps a neutron star within our own galaxy has undergone an accretion event has produced a very powerful relativistic jet, which is causing shocks and synchrotron radiation and is happening within our own galaxy. And there's all kinds of knock on effects for that there's a lot of injection into the surrounding interstellar medium. So this is really a first this program of monitoring all of these sources regularly all the time and really giving us an insight into particle acceleration in our galaxy as a function of time. Let's get forward to the end of the movie then let me highlight some sources here. So everything which has a box around it. We have discovered it with our myriad observations a large scale structure around it. And some cases these are large scale structures which look rather static so this is the long term action of a relativistic jet on the nearby interstellar medium. But in some of these cases we've actually observed jets launched for the first time, and we've seen them propagate through the interstellar medium and decelerate on time scales about a year. Now to put this in context and I'll come back to this in a moment in the entire history of radio studies of these kinds of objects. We had one example where we've managed to track a large scale jet for more than one year. We now have already five new examples from me a cat and it's really revolutionizing this field. And I think this is important for the chair and cough telescopes because we're really seeing in situ particle acceleration over a period of a year from relativistic jets within our own galaxy and we can monitor them. We can see when they re bright and when they might be most active. So let me just focus in on one of these particular objects this is from bright et al 2020 which was published in nature astronomy. This is a sequence of images we made with me a cat of this source and at later times with the VLA. The thing was we did not expect given the relatively poor angular resolution of me a cat so I should say me a cat is an extraordinary sensitive radio telescope but at the moment, until it becomes the SKA it's relatively poor angular resolution. So we did not expect to resolve jets from this source but we did expect to be able to monitor the core black hole for a long time. And in fact we monitored in the end for over a year. So you are surprised by around day 90 we were actually seeing a separated component, and we managed to carry on tracking this component. So this is the approaching side of a relativistic ejection. The central line is location of the black hole, and the receiving line is the appearance and propagation of the the ejected material going away from us on the other side. So to detect and track the motion of these jets for over a year, as they propagated away from the central black hole, and this really was a unique and really exciting data set. I'll just show you a few aspects of those data but I won't be able to summarize everything about those data right now. First off let me show you the light curve of the binary so what we see here is over a period of about half a year detailed radio flux monitoring of the emission from this black hole when it's associated jets. And I can identify a few phases I can say that probably what happened around here was an initial very rapid phase of particle acceleration, followed by a phase of adiabatic expansion from a relatively small size initially, which meant the electrons cooled very rapidly and we lost a electron emission. But then there was a long phase for over 100 days or nearly 100 days where we see the jets propagating through space, but they are not fading away very rapidly and this means that there must have been in situ particle acceleration. And ultimately we see that this deceleration is happening we actually see the components decelerate. And then later on, well I should say sorry, there is a particularly important epoch which I'll just focus on for a moment, which is here, where we observed the one of the ejected components from this black hole, at the same time with the one in radio telescope which is an interferometer in the UK, and with the meerkat telescope in South Africa. We observed them at the same frequency but at very different angular resolutions. Okay, so let me explain why that is important. What it does ultimately is it gives you the energy contained within that component or a lower limit on it. So, here are the observations which we made on that date. So, what you see first of all in this image here the central black hole is over here where you have the pointer. So if you look at these contours you can see that they are extended, and this is the meerkat image and we know therefore that there must have been a new component, which appeared over here. That's the kind of angular resolution that we get with meerkat. It's enough to say there's a new component, but not really enough to see it in detail. But with our Merlin observations, we managed to find we managed to see in a great detail the black hole over here but also exactly where this component was here. But what we also found, I should say, is that we measured more synchrotron emission, more flux with the lower angular resolution telescope, and therefore we were able to associate this missing flux with the range of angular scales between Merlin, Emerlin and meerkat. So meerkat has an angular resolution of a few arc seconds and measured two milli Janskis, Emerlin has an angular resolution of about 0.1 arc second and measured 0.4 milli Janskis. We can put these numbers together measuring the size is really the most important measurement when you want to do the energetics of the ejector. So we can put them together. And essentially what that tells us is that at 90 days after launch from the black hole, there was still over 10 to the 42 ergs. That's a huge amount of energy contained in the ejector. Furthermore, this ejected component was still moving superluminally, which is an effect you get from when things are moving intrinsically, not quite at the speed of light but highly relativistically, which meant that there was still more kinetic energy to lose. So this is a very strong lower limit and this is a huge amount of energy much, much lower than than has been often estimated for these kinds of sources previously. The jets, remarkably the jets from this, this source were also observed in the x-ray band with the orbiting Chandra observatory. So let me just focus on one of the epochs here this is from Espinacetel, but this is clearly this is where the black hole is and this is where the resolved jet component is. We can look at the spectrum from the radio emission all the way through to the x-ray band and we see that both regimes are consistent with a single spectrum of syncron emission from this component. And our best estimates of the magnetic fields mean that this means the electrons were observing in the x-ray band are TEV energy electrons that is that they have Lorentz factors of greater than a million. So we're seeing leptons, electrons accelerated to extraordinarily high energies in near real time in these ejector. Well we saw these ejected decelerate with time I'm showing you three panels here first of all these are actually now for three different ejections. And what you see is the distance from the black hole as a function of time. And if something continues to move at the same apparent speed you get a straight line. And what we're now seeing in every case is that we see these things move in a parent straight line or apparently ballistically for about half a year, and then we see abrupt decelerations. So in a nutshell what the ThunderCat program is showing us is that we're actually able to track relativistic ejections from black holes in our own galaxy. We were able to measure the internal energy of them were able to track them throughout an entire period of typically about one year until they deposit all of their initial launch energy into the surrounding interstellar medium. And by following up on these studies we're probably going to be able to place some of the strut the tightest constraints on the real intrinsic energy of black hole jets that's ever been possible. Of course those those objects are very good candidates to be high energy sources of the kind of thing that Cherenkov telescopes are interested in. But let me change tack now slightly and talk about exploitation of these meerkat data in another direction. So this is a project which is led by Alex Anderson who's a PhD student here in Oxford jointly supervised by myself and Professor Chris Lindtog. And what Alex has been doing is he's been using citizen scientists to look at the wide field images which we get from meerkat, which of course contain hundreds of radio sources. And to see if we can, if we can use sequences of those images to actually find transients and variables for the first time in the radio band. So you'll recall that I said earlier in the talk that you know it's easier to find new astrophysical transients or new extreme phenomena for the first time in optical or x-ray bands but there may be some phenomena, which are actually brightest and easiest to find in wide field radio data. And the way that we did this is we did it by employing citizen scientists, that is general members of the public who accessed our data by the Zooniverse platform. So just to explain what I mean this is, this is a single meerkat image, which is centered on a very interesting binary system called Sursonus X1. So right down here in the center of this, this little nebula in the center is a binary system containing a probably a massive star and a neutron star and we study this source intensively, and we look at how it varies. We're interested in this nebula, this little thing around it, but this whole field here within the enclosed circle is about one, it's about one degree diameter. All of this is image to high quality and there's lots of radio sources in here. And we make multiple sets of images of the same field, and we can compare those images to see if we find variables. So Alex together with our colleagues in the Zooniverse project launched on December the 7th last year a project called burst from space meerkat. And what he did is he presented to enthusiastic volunteer members of the public sequences of images from our meerkat data where our software had identified sources which might be variable. The members of public eyeballed looked at themselves with their own eyes and brains at these data and classified them as to whether or not they really thought they were transients or not. And the human brain and the human eyes as I'm sure you know appreciate are often much much better than any simple automated software you might be able to write finding these kinds of sources. So this is a project that's within the the the overall Zooniverse project, which is most famous for the galaxy zoo project but has done an enormous amount of stuff beyond astronomy beyond physics. And it's the largest citizen science project in the world. So what did we get. Well, here's an example of what the, the citizen scientists saw when they logged on to the program. So they were shown the light curve of one of many hundreds of objects within the field and they were, you don't really see it very well on this particular plot but these points have our bars this is a high significant source. And they were asked to say, based upon some training they'd be given whether or not that really looked like a genuine variable, and they were also shown images snapshot images of the source to say you know, so they could identify artifacts. They were asked a number of relatively straightforward questions which culminated in them saying you know, no I don't think this is variable it's an extended blob which makes it unreliable. It looks like some kind of radio imaging artifact or maybe it's a real bona fide transient or variable. So we set this going on December the seventh we closed it a couple of weeks ago because essentially all our classifications from our initial small data launch were complete. There was something like 10% of all the thundercap data. So a relatively small subset of our data. So in that data release which we released to the public there were nearly 9,000 unique sources across 11 different thundercap fields so about 11 different one square degree fields. So 89,000 individual classifications by 1038 different volunteers so essentially most sources were classified about 10 times which was our goal. And therefore, you know at that point we, we, we announced that the project was closed. This corresponds given the time of which this took to about one new classification every one to two minutes for a period of about 90 days. So there's some interesting sociology associated with these projects so for example the top 20, you know volunteer classifiers each classified over 1000 light curves and objects each. So we needed some way of identifying you know which were really likely to be the real bona fide transits now when we do this ourselves as astrophysicists with with you know much less manpower than 1000 volunteers. There's a couple of diagnostics so we produce a plot like this you see on the right, and we try to use this to identify where interesting sources might be which of course might be new exciting extreme astrophysical transients. So the the y axis here is a is a measure of the fractional variability so this is the amplitude of variability divided by the mean, and the x axis is simply the statistics of a chi squared the chi squared statistic of a fit to a flat line. I you know once you once you consider error bars is something significant variable. All of the sources which are circled our sources which we as astrophysicists, because of course we looked at this data beforehand to it to a relatively shallow degree had identified as certain or probable variables or transients. All of the objects which are not gray all of the objects which are colored. So the purple and blue things down here are objects which the citizen scientists identified as likely to be real transients and variables. Okay, so there's obviously for the things which we classified as variables they got, they classified as variables as well. But there's a whole bunch of objects, particularly in this part of parameter space, where things the variabilities perhaps a little bit less dramatic where the citizen scientists said yes this looks like a variable but we wouldn't have necessarily looked into that cloud of points because we'd have needed to look at well, you know, at 9000 different sources which is a lot of work. And we wanted to figure out some way of identifying one of the most likely ones so Alex has been looking at this, and at the moment he has eyeballed all of the sources for which more than 40% of the volunteers thought it was a real variable, and he's found that about half of those look like they're bona fide variables. So this means that we have about 160 new radio variables and transients just in this small subset of our data. And we don't know what they are yet this is this is a very small fraction of our initial sample we don't know what these objects are yet I'll show you two examples in the following slide but honestly there's a lot of potential discovery space here and this is only going to get better with time. And as I've already mentioned it's important to focus on or note the fact that he sits and scientists identified variables and transients that we as scientists based upon our preconceptions and limited resource would have missed. So let me just give you two examples of objects. Let me focus first on this this one here in the mid right. So this is an object which varies over time with a fractional amplitude of variability of about 50%. The y-axis here is the flux density or the flux that we measure of the synchrotron emission from this source varying between about 0.9 and 1.6 milli janskis over a period of about a year. These are our best estimates of error bars to the sources clearly vary dropped dramatically and then has risen again towards the end. We find a lot of sources which look like this, more than 50% perhaps more than 80%. So what we're seeing on that looks something like this. And these are likely to be low level activity from AGN it may be intrinsic variability or may actually be scintillation that is the propagation of the radio waves through the intergalactic medium makes them appear to twinkle. And it's very important this kind of work is very important because it tells us about the low levels of supermassive black hole activity throughout the universe in a way which perhaps isn't accessible via perhaps studies optical or X-ray wavelengths. More excitingly of course are you know bonafide in new transients which you know we really don't know what they are. So here's an example of an object which had a single bright detection early on and was never detected again in another image. And what we show here is a sequence of three snapshots of the radio image around where this source is. So this is obviously the detection image and this looks like a radio source. This doesn't look like some kind of weird interferometric artifact this looks like a real radio source. And in other images that you know you see all the structured noise that we're used to, but there's just no evidence of a source there at all. And we really don't know what this is there's no obvious counterpart in online catalogs and we're still, we're still moving forward. The next steps will be to relaunch this program with a lot more data, and also to use our classifications remember we now have 10,000 independent classifications of objects of radio transients or not, and we'll be using those in collaboration with colleagues in South Africa to train machine learning algorithms for the first time to to identify and possibly classify radio transients and who knows some of those might turn out to be objects which are very interesting for studies of the extreme universe in the context of things like the Cherenkov telescope array. I want to change tack again now moving back to a more specific class of object which has very very direct relevance for the CTA and the other Cherenkov telescope arrays. What I'm representing here is work which is led by my, my PhD student Lauren Rhodes and this is studies of the radio mission from VHE GRBs. Gamma Ray bursts are phenomena which I'm sure most if not all of you are aware, which has been known a long time since the 1960s they're short duration flashes of gamma rays from space, which probably have two different origins, one associated with the deaths of massive stars, and another one associated with the mergers of neutron stars which are probably also associated with gravitational wave events. In the last two or three years it's been become apparent that some of these gamma ray bursts and, you know, in fact, all from the longer class of gamma ray burst are detectable with ground based Cherenkov arrays such as Hess and magic. And this allows us to probe the very high energy emission from this phenomenon in ways which was just not possible previously. So, of course, one very interesting question is, you know, do the raid does the radio mission from these very high energy gamma ray burst does it look like the radio mission from other gamma ray bursts for which there's a large body of theoretical literature, and the somewhat smaller body of observational results but it you know there's a well developed theory of relativistic jets behind the radio mission from these GRBs. So here's the position in the first half of a PhD to jump straight onto this topic using a couple of the telescopes to which we have access and studied all of these VHG GRBs at the rate in the radio banter in quite some detail. So here's a result from one of the earliest VHG GRBs GRB 1908 29 a and this is from Rhodes et al 2020. This is one of the best radio data sets ever on any GRB not just a VHG GRB. And it combines observations which we made with the Amy radio telescope here in the UK, and to which I'll return shortly, and also with with the me at radio telescope which I've mentioned down in South Africa. So here's an extraordinarily nice data set and what it shows the combination of the data at the two very different frequencies 1.3 gigahertz, relatively low frequency and 15 gigahertz relatively high frequency, showed that there was both a forward and a reverse shock in this camera burst. So this means that as the relativistic ejector as the jet left the camera burst it propagated into the installer medium. So with the installer medium the jets hit it and a shock is propagating through the installer medium in the frame of the jet, the installer medium is hit it, and a shock is propagating backwards. Through the camera through the jet material, both of these accelerate electrons and produce shocks with similar physics, but different micro physical properties. The mission suggested that there was an early time reverse shock which later on became a forward shock, and then at later times we saw a plateauing or a flattening of the radio mission, which suggested that at late times we were detecting the host galaxy. And there's some interesting detailed physics which came out of this, such as the suggestion that this one exploded into a low density medium, and had a relatively low kinetic energy. This is a recent paper which is just about to be accepted and in press. So those of you are interested in this area may see this on the archive in the next week or so. It's on this GRB 2012 16 C. Now in this GRB. And then a very high energy GRB but the ratio of gamma rays and x rays to optical emission means that it can be classified as what we call a dark GRB so this means it has much lower or significantly lower optical emission than we would expect given typical particles and the obvious interpretation of the typical interpretation of that is that some of this optical emission is being absorbed by dust, perhaps in the galaxy or perhaps even in the immediate environment of the GRB. The study of this GRB led to some very interesting results or as I say this from Lauren's paper which you'll which will shortly appear so she combined some early time optical data with some very detailed radio observations, both with Berlin with me a cat and with the VLA in the United States, and it's impossible to fit a single forward shock model to these to these ejector to these data. And a single forward shock model is often fitable to radio data from gamma ray burst but in this case it was not and maybe that's just because these data were very good or maybe it's because there's something unusual about this event. The easiest interpretation of what's going on actually is if you look at this schematic over here so here's the observer he's there the cataclysmic event which produced the gamma ray burst. And as with all gamma ray burst a highly relativistic jet came straight towards us, there's a forward shock and that produces bright early time radio emission, but it also seems or it's also easiest to model some of the radio emission with a more mildly relativistic wider angle emission or ejector, perhaps, you know as low Lorentz factor is one or two, which you actually still carrying a significant amount of the kinetic energy, and it's producing late time radio emission. Well this is very interesting because this kind of model is actually similar to the models that people have put forward for the for the gravitational wave gamma ray burst event GW 170870. So when Lauren looked at all the gamma ray but the VHG gamma ray burst together and put them in the context of normal or non VHG detected gamma rays gamma ray burst it's not clear that there is any difference in the population. So what you see here is redshift corrected days since the burst. So what you see here is the the the monochromatic luminosity or the radio luminosity from each of these grbs as a function of time. So the gray points you see in the background or a selection of non VHG grbs and the blue points are the VHG grbs which Lauren has been involved in observing at radio wavelengths. The first thing to notice that if you look at the overall distribution of luminosities of these objects then you know and applied, for example something like a column or golf spurnoff test, you wouldn't be able to see that these populations are different. I mean they're probably given the, the low sample size we can't say these populations are different, but it is very interesting that note to note that two of the VHG grbs are particularly low luminosity. And again that's probably a selection event effect because it's easier to detect the very high energy gamma rays went for relatively nearby grbs. So at the moment we we don't know but of course you know it might be that with a bigger sample we do begin to see some differences and of course this is an extremely exciting and interesting area of research potential for the CTA. So let's talk about one more science area which I think would be interesting to the CTA which I'm certain would be interesting to the CTA, and it's observed in the radio band before I just discussed briefly a little bit about where radio astronomy and radio rays are going to go in the next five to 10 years. So excitingly, there is a possible association between a relativistic jet from a tidal disruption event and the detection of an astrophysical neutrino. So in a nutshell the story is that we see a supermassive black hole or a relatively low mass supermassive black hole, perhaps only a million times the mass of our own son so something like the black hole at the centre of our own galaxy, appears to have torn apart a nearby passing star so that about half the mass of that star becomes tightly bound or becomes gravitationally bound to the black hole and accreted. So first of accretion onto this supermassive black hole, this produced amongst other things a powerful relativistic jet. Now the radio data on this object as I show in a moment is so good that we can see that for up to at least half a year after this event began a powerful jet is being produced and about, and at about half a year. The neutrino was detected by ice cube, which has a fairly strong probability of being astrophysical so it's a very exciting possible association. So, let me just put these time disruption events in context so this is a, this is one way of representing the whole range of black holes and accretion across the universe. So what I'm plotting here is the mass of black holes and what I'm plotting here is the relative or fractional rates of accretion onto these black holes in units of Eddington which means that they should be about as high as they can go. So the extra binaries I was talking about earlier in the context of the Thundercat project there at the lower end and that's actually handy because we can we think we understand how those can be created. They're in the same mass range as the the LIGO black holes and neutron stars which we see at the highest mass end are the most massive AGN at higher accretion rates and at the highest mass but low accretion rates around 87, which has been so spectacularly imaged by the event horizon telescope. The tidalist disruption events are super massive black holes but as I say perhaps only a million or 10 million solar masses, and because they experienced very rapid changes in the accretion rate we actually think that we can, we can understand a lot of what they're doing in the context of patterns that we've learned about x-ray binaries so that makes them of particular interest to me, but of course the you know the possible detection of very high energy emission I think makes them very interesting to all of you. So this is these results are from a paper published by Stein et al last year they made the cover of Nature Astronomy a new source of neutrinos and in a nutshell then for those of you who haven't seen these kind of schematics before. The idea is that a star passes too close to the gravitational influence of a supermassive black hole, it becomes distorted, something like half of the star ends up spiralling towards the black hole producing an accretion disk and ultimately a jet, the other half is unbound and basically splayed out across the environment of that black hole. The ice cube neutrino detector detected detection of a probable astrophysical neutrino prompted a search with Zwicky, which is an optical transient facility. Zwicky found in looking at their data that there'd been an optical variable in the direction of this neutrino for actually half a year already, and the combination of the optical monitoring with the neutrino detection and subsequently radio monitoring put together a really nice story. This is time since discovery of the TDE but what you should start off by looking at is that this vertical dotted line here this is the time when the astrophysical neutrino was probably detected. Now ice cube independently estimates this has something like a 60% probability to be astrophysical so that's tempting but it's not super convincing. However, a jet bright tidal disruption event in the same patch of sky combined with this brings the probability down to significantly less than 1% so actually makes us moderately confident they're associated. So what we've seen then looking at the the optical data was that they've been an optical variable identified now as a type of disruption event for half a year before the neutrino was discovered. Excuse me. In radio monitoring observations we now can see or we could see then that there was something unusual going on in the radio. So here is a sequence of radio spectra from one gigahertz to about 15 or 16 gigahertz taken at four different epochs so between 40 days and 180 days after this initial event so I recall the neutrino was detected around the time of this last epoch of radio observations. So the key point to take away here is that there is a peak at all times in the radio spectrum, and that very strongly implies not only that there is ongoing energy injection into whatever that's producing this radio mission a relativistic jet, but also that we can calculate the size of the ejector from from measuring that peak. We're able to do that and we're able to see that this is since a function of time we can make measurements associated with these four peaks, we get the size of the ejector as a function of time, which tells us that it's expanding mildly relativistically, and we get the internal energy, which tells us that energy was still being pumped into this jet, at least up to the point where the neutrino was detected. So there's a very nice circumstantial background picture here, which suggests that a very powerful jet from this black hole was being produced at the time the neutrino was detected and I think this is, you know, this is a very exciting probability. The reason that this is exciting or one of the reasons this is exciting is that if you see the neutrinos it tells you that hadronic processes I processes associated with a with a proton are involved. So if you just see gamma rays alone and this could also always just come from leptonic processes, such as direct synchron or inverse content emission. So this is a summary of what we saw, and I recommend those of you are interested and haven't read it already to read Stein et al 2021. So those were there the astrophysical things or radio sources that I wanted to highlight a subset of all the things that's going on in the radio band. So here's your little feel for what's going on then with the development of radio telescopes and over the next five or 10 years we're really looking at a development from the current new generation, which are fantastic towards the square kilometer array, and the next generation VLA, but I think it does raise a question of where will we get our high cadence monitoring data from, which has been really essential for these transient studies. Here's a picture of me account, as it was as it is today and as it was at its inauguration two years ago. On a timescale of about five years, me cat will become SKA one mid. So that means the mid frequency component of the square kilometer array. For all of the science that I have talked about today, all of the syncron science, this is going to be the most exciting and important component of the SKA and it's going to be the most important radio telescope in southern hemisphere. It's going to increase the sensitivity of me cat which is already extremely sensitive by an order of magnitude and increase the angular resolution by more than the order of magnitude. There is another component, a low frequency component, which is under construction in Australia, but my sense is that for most of our physics, it's going to be a little bit less important. The next generation VLA, it's hoped to start construction on around the same timescale, and it's hoped that it will be at a stage by the end of this decade that'll be more sensitive than the existing VLA and maybe has full operations if it gets fully funded by about 2035 and that will in turn be the most powerful radio telescope in the northern hemisphere. So this is already a shiny new radio telescope producing fantastic results in the future is looking very, very bright that this has become more powerful and more exciting and it's a very exciting time for radio studies of transient. However, let me just raise one point for you to think about. So the SKA or the next generation VLA if you're using something in the northern hemisphere will be the main facility for radio science in the 2030s. And it may well be that in the era of the SKA the other radio facilities become off board because it can. It's the nature of the beast with radio telescopes and it can do essentially everything. However, as you will have seen a lot of the science that we've done over recent years, some of which I've highlighted has been with sources which are much brighter than you need the SKA sensitivity for. And if we only use the SKA to its fullest capabilities observing very faint objects will miss a lot of these nearby objects we don't need this sub micro jancy sensitivity to monitor a lot of these bright transients. Now optical astronomy also face this issue and up to astronomy responded by building large numbers of small telescopes to do optical transient surveys. However, the radio astronomy world might not do this and the reason the radio astronomy world might not do this is because the SKA can in principle do this as well. So remember, even though it's a large array, it also has a wide field of view. It's actually sub array which means you could you could branch off small numbers of antennas to do monitoring of bright sources. But my concern is that you know will this really happen this will make scheduling extremely complex. And I can imagine and I could imagine being in their shoes people proposing to observe extraordinarily deep with the SKA will not want some transient scientists using 10 or 20 of their antennas to monitor some title disruption and gamma ray burst gravitational word gravitational wave merger event. So another possibilities which I'd like to see into your mind is that maybe it you know now is the time to consider actually building a small dedicated array in the southern hemisphere for rapid radio follow up and monitoring of transients and radio mission associated with with extreme astrophysical sources and you know and I just I'll highlight the case of Amy which is a radio telescope we use all the time. This is two antennas of the Amy larger a this is me with some of my team when we visited a few years ago. There's actually six antennas used in Amy. It has short baselines the dishes are more than 50 years old it's extraordinary this is very old. It's a very good condition you can use them up to high frequencies, and we use them all the time. And they are monitoring transients more than 30% of their program it's an extraordinary program high cadence. We are associated with many, many publications lots of nature and science papers. These figures here are just a number of figures where Amy has made a vital contribution to extreme transients astrophysics just in the last. So this is for example this is the light curve I was showing you earlier of a stellar mass black hole this is the neutrino TDE, Amy contributed to that study. This is a long term study the jet from a different type of TDE. This is radio flaring from a cataclysmic variable that is a white dwarf. This is radio monitoring of the extraordinary radio history of a transformative supernovae. This is radio monitoring of the very high energy gamma ray burst, all of which, you know, Amy made a very important contribution to. So you don't need to escape to do all any of this and my concern is that perhaps this stuff won't get done if we only have SKA. So perhaps you know I just see the idea in your minds perhaps we do need our own dedicated radio transient array or arrays to do this kind of work in the future and really support the work of things like the chair and cost telescope array. So I will wrap up there radio transients studies I hope I've convinced you is an extremely exciting field it's a growing field. And we're getting to play with a lot of really exciting new radio telescopes and discovering lots of things. Nearly everything we're studying has a counterpart at higher energies and there's real synergies between studies and x rays gamma rays and the radio band. Here cats are favorite toy at the moment my group and others around the world are getting extraordinary science out of this covering black holes of all masses gamma ray bursts. And also you know really opening up this field of commensal transients just doing transient surveys where you find the transients for the first time in the radio band and I love the fact that we're doing this with citizen scientists it's really it's really been a fantastic story. So I think the future is very bright for synergy between radio observations and chair and cove and and other high energy telescopes but I do as I say you know just think let's think about whether or not the SK a low will deliver everything we need to monitor the sources. And I will stop there thank you very much for your attention, and I'm very happy to take any questions.