 So, good morning, everyone. Thank you for the invitation to talk about this very timely, I would say, subject. And I hope I'll convince you that small telescopes will play a very important role in the coming years, not only because of the city a, but generally speaking, in this new era of large scale surveys. Like CBS4 in the radio and very soon LSD in the optical. And of course, size does matter. So there is science cases that you can only do with big telescopes. But I will argue that there is a lot of very interesting science that you can only do with with small telescopes. And there is also a lot of science that you can doesn't really make sense to do with with the big telescopes. So, especially, you know, in connection with CTA, I think it's never too early to start thinking about the interesting synergies and ways that, you know, we can build up the community and our instruments and capabilities in support of of the large scale surveys. And this is particularly important for polyametry because they're not a lot of telescopes in the world with polyametric capabilities and the reason for that is that polyametry is hard, and people try to avoid it as much as they can, but also the universe is not very polarized. And this is because it's dominated mostly by thermal processes and thermal processes don't really have a reason to make polarized light. But there is also a lot of symmetry in the universe. So for example, if you take a look at the sun, and you look at different regions on the sun, then you will find that this is very polarized source. But if you look at any other star in the sky, which is far away and you get a mission from from the entire sphere basically cancel out all the polarization. And you see some unpolarized source. So we need sort of ways to break that symmetry and the best is using magnetic fields. And magnetic fields are responsible for what we call non-thermal processes. The most famous of one is obviously singleton radiation, which is very, very polarized. But magnetic fields are also very important for many physical processes that are happening in a lot of different sources that are, I think, very relevant to CTA as well. And I will tell you a little bit about those sources starting from the small black holes and I'll make my way up to the bigger black holes. But before I do that, let me tell you a little bit about how we measure polarization in the optical. And there are of course different ways you can do it, but the basic principle is the same. You have light coming in from your telescope on the left here. And then you have some halfway plate, some birefringent crystal. Nowadays, the most common one is what we call the Wallaston prism. And then you have your detector, which for optical telescopes, that's just a CCD camera. So the main idea is that you will rotate the plane of polarization using the halfway plate and you will measure the intensity of the light coming from your source in different angles. And you need at least four, which you can see up there at least for linear polarization. And if you measure the intensity of those four different angles, you can combine the measurements, estimate what we call the Stokes parameters, and then from that calculate the polarization degree and angle of your source. As you can imagine, this is a very inefficient process, and it takes much longer to do a single measurement that you would normally do with just doing photometry. And of course, while you do your measurements, you assume that the sky and your source have changed, and in many cases this is not really true. So that introduces systematics that then cause you problems and really limit how faint or how low polarization you can measure. So people have been trying to be sort of creative with their designs and try to overcome some of these difficulties. And one that's been been developed at the University of Turku and one version of that is at the Nordic optical telescope is the typo two polarimeter, which is basically has the same design you have a halfway plate by a fringe and crystal this case a calcite block. And then you have your detectors but instead of having one CCD camera you have three, and you send light in all three so basically send a different optical band in CCD. So it still takes you about the same amount of time to do the measurement but you get a lot more color information out of that. The end of the art at the moment is what we call one shot polarimeters, and one of the earliest design are the one you see here which is robable, which I'll tell you a lot more, more about where you have two halfway plates, and two wall of some prisms side by side. There are no moving parts, and as light comes in from your telescope, get split simultaneously to four different polarization orientations. But then you just do photometry on that and measure the stocks parameters and all the polarization information we need in just a single exposure, which makes a very efficient instrument for for monitoring. I'm just wondering what that looks like. This is an actual image from robable where every cluster of four spots that you see like this one here corresponds to one source on the plane of the sky, which is projected in four different orientations on your CCD and of course we the source that is of interest to us we put it in the center where we have this mask, and that allows us to block any unwanted light and reduce the background which allows for much more precise measurements of the polarization. I will be, of course, talking a lot about robable but I cannot not acknowledge all the many different small telescopes around the world from Japan to Hawaii and everything in between that over the years have really produced a lot of very interesting science. And I'll mention some of those those results. Of course, I cannot mention everything. So, I apologize in advance if I don't do your telescope or your, your results justice. And towards the end, I'll tell you a little bit about current efforts to coordinate many of this small telescopes for for very exciting science projects. So for robable, we are a small collaboration of about six institutes in three different continents, but our base is the University of Crete and the skinnecus observatory that you see here, and we're using for all our observations the 1.3 meter telescope. And that's here and that tiny instrument you see down there that is robable is actually very compact and easy to move around. Our primary objective was to study blazers, and in particular wanted to study a unique phenomenon that happens in blazers which called the rotation of the polarization angle, and I'll tell you more about that. But of course, if you have a good polarimeter in your hands, you want to do other other science as well and we try to do as much as you know, we could. And I'll tell you a little bit about about that as well but if you see something that of interest to you and I have not mentioned it please feel free to to ask me about it. Starting off with the small black holes, and the ones that make very, very energetic events that I'm sure are very, very much of interest of cta are jrb's and jrb's can be highly polarized, and you can see here the really beautiful results from the Liverpool where they found that very early times, a high degree of polarization up to 30, 30%, which seems to go down a little bit but sort of, sorry, stabilizes around to 20% and at the same time the polarization angle was roughly constant. Of course, this is not all jrb's are polarized and of course they show very different behavior. So just a year later, we observed our very first jrb with the robo pole at similar times case was very, fairly close to to the burst and we saw a very different behavior. So we now see very low degree of polarization, about 2%, which is constant. And as it turns out, this is most likely coming from the dust in our galaxy. This is what we call interstellar polarization. So basically the jrb was less than 2% polarized in this case. We had another jrb observed very recently, and we're now looking at time scales which are much larger. So, and we see do see very different behavior well so in the beginning, there was, you know, very low degree of polarization although in this case we think it's very intrinsic. And then suddenly towards the end of observations we see sort of a jump in in the polarization degree and change in the polarization angle. So this is the very first time that the polarization evolution of a jrb was was actually followed that that late. And this is the first time we've seen that sort of jump and it's not exactly clear why that would happen, although there are just a couple of models that that could could explain that but that just tells you, you know, how how important is to do polarization of the jrb and there's still a lot, a lot to learn from that, what probably will be much more of interest for for cta folks is the very recent very bright jrb which I'm sure you've, you've heard about that happened just two months ago. And that would really have been a very prime target for cta because it's very bright in gamma rays and stayed bright for a very, very long time. Unfortunately, there was bad weather at the skinnecus observatory at the time, but we did manage to get observations with the Nordic optical telescope which is in La Palma so just next door from when we're cta would be. We got some measurements with that and and what's very interesting is that in this case we also managed to get measurements using the imaging x-ray polyametric explorer. So this is the first and maybe the only jrb that we were able to get both x-ray and optical polarization measurements at the same time they were to GCN associated with those measurements. So that the polarization in both x-rays and optical is low, but that's all I'm allowed to say at this at this point, but you know if you're really interested in that don't on disparages yet. There is a paper coming out very soon that that has all the, all the information. Moving on to another class of objects that I think are very interesting to to cta and that is binaries and especially the class of they call gamma ray binaries and now there are a few that have been detected by Fermi and there's a couple that have been detected also in in very high energy gamma rays but of course cta will will detect a lot more of the sources. And what I'm showing you here is the results from the canada telescope at the University of Hiroshima, looking at the bright outburst that happened in v 404 Sydney in 2015, where there was quite a bit of polarization they found about 8% polarization that that turned out to be interstellar and you can see that here where basically the the line show you the orientation of the polarization. Blue is for the source the red is for the nearby stars. And as you can see that there's sort of line and this kind of a smoking gun for the interstellar polarization you can really see that when you do the in this plot where the position angle versus polarization degree you can see all the stars are in that direction. And of course at the bottom here you see some messy the modeling of the source and it is obvious that all of the gamma ray information is missing. So that would be really great to have cta cover all that range and then with the constraints also from the low energies. I think it would be very important in understanding the underlying emission processes and the sources. Moving on to the sort of bigger black holes, and there is a type of sources that I think are not being, you know, gamma ray community has not paid too much attention to them and I think they really should and especially think cta should start putting them in in your radar, and in order to tell the disruption events. This is basically when a star comes very close to a black hole, close enough for the gravity of the black hole to overpower the self gravity of the star, and at which point it will sort of rip it apart and consume its gas by forming and a Christian disc. Now we had sort of models of how that star capture what happened since you know back in the 70s but basically the way we observe the sources. Today matches closer to what's risk predicted in 1988 and very soon after the rosa, which was an extra satellite detected the first events. Now we think that those happen at the rate of 10 to the minus five per year per galaxy, our actual classification rate at the moment is 10 to 15 events per year. So basically talking about spectroscopic classification. And in just a couple of years from now the expected rate of discovery from LST would be 10 to 20 events per night. Of course, this is the discovery rate so that a lot of the events will be too faint to do anything about. At least in the beginning a lot of them will go unclassified because they're simply limited amount of time for for spectroscopy and follow up observations. But you can imagine that slowly will build a big enough sample of spectroscopically confirmed TVs that you can feed your to your machine learning network and train it so that it will be able to identify the TVs from the raw data stream of LST. So at that point you will have a much a very big population of transients that you could be looking at. And I think those should be of high interest of course it a because there is a lot of discussion that this might be multi messenger events and there is some some discussion that they could be accelerating ultra high energy cosmic rays. There are a couple of papers now suggesting that this could be neutrino emitters. And this is from one of such paper from from Nelson et al where you see the outburst in optical is this red and green points, and then the blue and purple ones are the dusty echo that comes later. There is sort of a neutrino that's coming at the peak of the infrared flair. There's of course already some theoretical motivation and work where the neutrinos and the gamma rays will be made in this sources. The expectations now are not optimistic, but there's a lot of uncertainty and and the models and the reason for that is that we don't fully understand. How exactly does this disruption happens, how the accretion disk is formed, and why do we, you know, some CDs seem to be very bright in x rays, which is what you would expect from a super edit on event. While the majority that we see in the majority that LST will be refining very soon. And there are two scenarios for that one is that the accretion disk forms very rapidly. So as soon as you disrupt the star, the gas quickly forms the accretion disk starts ready radiating x rays, but there is a lot of gas from the start that hasn't made it to the accretion disk. And that gas will form sort of a screen and they will absorb the x rays and then reemits them to optical and UV. And in that case we expect to have a sort of a low degree of polarization. The alternative is that you have a slow formation scenario where the gas doesn't circularize quickly enough. And instead, as it goes around the black hole, form shocks at the Paris center and the apple center of the orbit orbit, and then the shocks make optical and UV and the process circularize the flow into an accretion disk. And in this case we expect to see high and viable degree of polarization. So these are our first attempt into understanding the polarization properties of of DDE is using Robel and an optical telescope and you see here, sort of the results this is one event called at 2020 MOT and you can see the ZTF light curve, which shows a very evolution. And at the bottom here this is the very first polarized light curve of of a total disruption event, which only consists of four points but there's a lot of information in this for observations. And first of all, we found that these can be highly polarized up to 25%. And this is without a jet. There's no no jet in this, this particular T what is really important was we're actually able to map the kind of evolution of the to the evolution of the title shocks that we know from the slow formation simulations. So we are fairly confident that least in this case, this early accretion disk formation happens through title shocks. And of course, this is, you know, just one statistics of one. We don't really know whether this is the standard picture for all CDs, or this is some some exceptional event but we're doing the best we can to observe more of this CDs in polarization. And then very soon, we're going to know if this happens all the time, or in very exceptional cases, but you can imagine if we sort of succeeding understanding what's going on will set framework where we can build all our models. And then with the constraints that come from from CTA we can understand the whether the sources are indeed neutrino emitters or not. Now, moving on to blazers have a single star but you have a continuous stream of gas flowing to the black hole and it powers very highly relativistic jet that's pointed towards your line of sight. And then we're seeing blazers will turn out to be really the bread and butter science for CTA. And there are a lot of different questions that we want to address. Some of them are very basic ones, like for example, you know, what is the jet made up of, and what is the origin of the gamma rays that we see in blazers. You know, understand a little bit more about how particle acceleration happens in the jets, and maybe finally differentiate between shocks and magnetic reconnection as dominant mechanism. So for the origin of the gamma rays, there are basically two scenarios with either looking at electrons in the jet and electrons make high energies, high energy radiation through inverse Compton scattering. So basically, they propagate in the jet, they see some target photon field and they upscatter it to higher energies if this is an external photon field of the jet we call that external Compton efforts from the jet itself. So the lecturers make the photons and upscatter them. We call that single terms of Compton. The alternative is that you have protons in your jet, and the protons make synchrotron, or they will interact with other protons other photons make pions, and then pions decay to secondary particles and gamma rays. So this, you know, the distinction between the processes and the question of the jet composition is is also very timely because of the, again, possible neutrino association with with blazar, and at least in the initial results from that show that neither a purely elliptonic or a purely hydronic model can explain both the multi wavling and the neutrino emission we saw from from that source. So with all we'll take it sort of a different look on that problem in a jet composition through circular polarization. And basically if you have an electron positron jet, then you will cancel out the circular polarization signal. If instead you add protons in your mix, then you break the symmetry, and you get a small amount of circular polarization with depends on on a couple of things but also depends on the level of the linear polarization. So we were able very recently to observe two sources. There are famous blazers with the 1.9 meter telescope at the South African astronomical observatory. And we didn't get a detection, but we were able to place a pretty good upper limit of about 1%, which really allows us to constrain the parameter space both in terms of the magnetic field that you have in your emission region, but also the positive fraction. So this is basically the fraction of of positrons to electrons and everything else is protons to preserve your charge neutrality. So for, and this is basically the results you see here. And for proton models to be doing efficient you need high levels by values of the magnetic field, and you need to low levels of the positive fraction. So you have a lot of protons high magnetic field and all that region as you can see is excluded by the observations. You can have any jet composition but then you need to be at very low magnetic field value, which then proton models are not very efficient, or you can have any magnetic field value but then you're in a regime where most of your jet is made out of electron pairs and you have only a few protons. And that also is not very helpful. So at least for the, you know, from the point of view of the circular polarization in the optical, if, if your chinos are indeed associated with lasers, then that needs to come from either some extrinsic event, or this hybrid or what is called leptochadronic models or subdominant hadronic populations. And this is where really CTA comes in handy. And because if you have all these leptochadronic models and the subdominant proton populations, then you should see something stick out in your gamma ray spectrum. And this is basically what you see here. If you're only looking at electrons, there's no reason for inverse complex gathering to do anything else about a smooth curve as as you see here. So you can imagine kind of the constraints from both the circular polarization and the composition of the jets and also the spectrum from CTA will be very, very important in our understanding the underlying high energy emission processes and the sources. So thinking about particle acceleration, you heard from George, your math in the previous seminar about a very exciting results on my current 501 and the very first detection of extra polarization from from a blazer and that really points us to shocks being the the main particle emission mechanism and the jet. Since then we've actually measured a couple of other sources and we're basically getting the same, the same behavior. But all our observations so far happened on when the sources were in an average state. They were not not really in quiescent but they were not really flaring either. So at least for the sort of steady state emission, we are fairly confident that shocks are the main particle accelerators here. But we don't really know what happens during outburst and we've seen some very extreme behavior when blazers are are flaring, although we are trying with high speed to get sources in flaring states at the moment but still we don't have any we're not very lucky with that. So in Europe, we try to understand a little bit more the role of magnetic fields and in that particle acceleration process. And as I've said, we wanted to understand more of this unique phenomenon of the rotation of polarization angle. So basically the polarization angle in blazers varies stochastically until it suddenly doesn't. And suddenly we'll start going through this monotonic rotation towards one direction that you see in red here. And then was it stopped doing what it's doing, it's just going to continue on randomly fluctuating. So we managed to detect a large number of this rotations, we basically triple the number of non rotations in just a couple of years. And then we started exploring their properties. And one very interesting connection we wanted to explore is the connection with the gamma ray activity. And this is what you see here. So basically what I'm showing you is the time difference between the middle point of rotation and the peak of the nearest gamma ray flare as seen by Fermi. And as you can see this time difference is certain very much about zero. So every time we would detect the rotation, there was always a gamma ray flare coming with it. And statistically speaking, this is very, very unlikely to happen just by chance. So we know that the rotations are very much connected to gamma ray activity, but it turns out they're also connected to very high energy gamma ray activity. And you see here some really good results from the magic collaboration on 0716, where there is no flaring at that very high energy gamma rays. There is then X-rays optical all the way down to 15 gigahertz radio. And you see also this very fast rotation of the polarization angle, which I may have the blow up here, where it was captured by a few different, a few meter class telescopes. So this was interpreted as shock-shock interaction. And that is because when looking at WBI maps, they saw that there was a moving feature that crossed a standing component in the jet of 0716. So basically you have a shock that's moving in the jet and it hits the stationary shock and you have all the flaring up to high energy gamma rays and you see the rotation of the polarization angle. We saw a very similar behavior in different sources a couple of years later. That's from what you see here from 3C454.3, where again we see a lot of flaring across the different bands from gamma rays all the way to infrared. And we see this drop in the polarization degree, which is very sharp. And at the same time we see this rotation of the polarization angle. Again, if you look at the VLBI observations, we do see something moving in the jet and as soon as it breaks out from the core of the blazar, then we get all the flaring and the rotation of the polarization angle. So we're very confident that we're again looking at shock-shock interactions. But then just last week when I was showing a part of those results to the IU Symposium that happened in Kathmandu, after my talk Houching Zhang came to me and showed me this figure and told me I have simulations from magnetic reconnection that do exactly the same thing. And this is basically what he was talking about, where you again see there is flaring and optical and gamma rays here, there is a drop, the polarization, and there is also the rotation of the polarization angle. So we're really back to scratch. We have two models and both can give you exactly the same results. So the way out of this is to push our limits basically and get more of these events, go to higher energies, and CTA will be very helpful with that. And of course go also to short timescale, the shortest timescale variability, which starts to become important to differentiate between shocks and magnetic reconnection. And you see here some very nice light curves, again from magic and different energy ranges from a current 4 to 1, which had an outburst very recently. And on the left side I'm showing you the work from Yeni Jermanainen, which will be available soon, where Yeni made a heroic effort to do a framework for the proper comparison between simulations and light curves. And I think that will be very, very important for CTA because now we can only do the very short timescale variability, light curves for just a couple of sources in very bright states, CTA of course will be able to do it for much more sources. And I think it will be very, very important. So at the same time, we have to also build our, you know, polarization capabilities and be able to follow this short timescale and support also the CTA observations. And we've since a year ago, we've been trying to coordinate different telescopes across the world to manage to do continuous more than 24 hour observations in the same way that like Fermi does, right? So we can have a, you know, an apples, apples comparison between the different light curves. And of course the problem we're facing is the sun. You know, unless you're at the polar cycle, at some point the sun will come up and you will have to stop observing. But you can use the Earth's rotation to your advantage. And you can imagine the scenario where you start observing in Japan and by the time the sun comes up, it's night in Europe, by the time is morning in Europe, it's night in the United States. So if you place your telescope in strategic locations, you will be able to do an uninterrupted, you know, continuous monitoring of your source. And that came, we came to call that non-stop polarization experiment, which consists from a lot of adventurous people and 15 telescopes across the world. You can see here that both the list of the adventurous people and the different telescopes, the bigger telescope we have is 2.4 meters. Everything is much below that. So we had our first one in November with a combine of 685 telescope hours. Of course, we lost a lot of that due to weather, but we were able to get pretty good coverage for the two targets that we had at the time. The time one was be a lack, which was going in, was at the prolonged outburst and also to 11, which is a historically highly polarized source, but at the time was in a very low state. You will see the historical quiescent state. So just to give you an example of how you can sort of fill up the time. This is the results we have from from be a lack and the top is the polarization degree in the bottom the polarization angle. Of course, you know, we start with Japan and the canada telescope and then soon after Aries in India starts observing and then we had a bunch of different telescopes in Europe. And finally, you have the US and Mexico. And just to give you a sort of how the full data set looks like now the top panel to show you the brightness of the source in magnitude. And as you can see, there is a lot of micro variability there there's a lot of clear, you know, flares that could only properly capture, because we have this discontinues more than 24 hour monitoring. This is still a work in progress or we're still working on on the data and the interpretation, but you can think of it at this point as just as a proof of concept that you know we were able to do this more than 24 hour observations. And I think when CTA comes online, there's be very interesting for us to have join join run together and I think there's be plenty of very exciting science there. So let me just finish by telling you another I think very interesting synergy between polarization and CTA, which has to do with unidentified CTA objects. And of course there's going to be an extra galactic survey from CTA and I can bet that you will find gamma ray sources that you were not expecting. And maybe polarization can can help us figure out what what those sources are and this is a work we basically started doing because of the Fermi unidentified sources and you see here one example where Fermi tells us that somewhere in this red circle this is a 95% error of Fermi. There is a gamma ray source, and you can see, you know, there's plenty of optical sources in that. The idea is that, you know, if you look at the statistics of the gamma ray population. If you're making gamma rays, chances are that you have some sort of a jet and jets make synchrotrons, synchrotrons polarized. So then, could be that if you look at for polarized sources and that maybe that is also the gamma ray emitter so we did some simulations where we placed basically blazars in different locations in the sky. And we tried to estimate the fraction of time that blazer would be much more polarized on the stars around it. And if you're looking at, you know, above the galactic plane, where the interstellar polarization is, you know, about 1% or below then, you know, more than 70% of the time. Blazer is far more polarized than the stars. And then of course we try to demonstrate this idea by observing all the sources you see here with the cyan circles and this is what the distribution of that field looks like in polarization degree. These sort of all the stars are sort of low polarization degree and then there is one source that is sort of far from the distribution in which we call the unidentified gamma ray source candidate. And what is very interesting is the fact that we were looking when we started this work, we're basically working with a three FGL, and our candidate source was just outside the 95% confident region, just inside there was a radio galaxy, and at the, you know, within one sigma, there was a radio source which we don't really know that much about. Now when the fourth Fermi catalogue was released, and they had, you know, twice as much data, much better visualization, both in terms of the uncertainty but also, you know, the exact location of the source, the position of that that identifies or shifted and now our candidate is within one sigma. The visualization knew which one was the source making gamma rays, even before Fermi could get could get a good position of it so I think there's there's a lot of sort of interesting synergies with with CTA as well on that front. So I will stop here. And I hope I convinced you how small telescopes can be can be very important for for CTA and how polarization can be can provide exciting synergies. And, you know, of course, as I said, it's not really not too early to start thinking about what we can, you know, do together and how we can build that community and I think it's in CTA is best interest to also get its own dedicated polarimeter. But I'm happy to hear your thoughts on that. Thank you very much.