 Thank you very much for inviting me and I will try to explore what is the city and the gravitational wave observer is. So let me start with the new window that was recently opened into the universe through gravitational waves. And in particular I want to say you that currently the detectors that observe the sky through gravitational wave are currently in a phase of upgrade. And they will start to observe again next year with the better sensitivity. And what was so far the gravitational wave astronomy so we had the three very important run that really start the gravitational wave astronomy. And in each of these run we increase the sensitivity that means that we increase the volume of the universe up to which we can observe gravitational resources. And in particular you can see in the box some number that correspond to the binary neutron star merger range. That means the distance up to which we can observe the system taking into account the sensitivity in the sky and also all the orientation. And you can see that we observe larger and larger volume and in the future we will observe also larger volume. And this enable us starting from the first event in which there was the first observation of gravitational wave with the three events to increase a lot the number of sources. And in particular, in the second round we arrived to 11 sources and the spectacular gv 17 17 which include the binary neutron star a binary neutron star merger. And now in the last round we arrived to 90 events the majority of them are binary neutron star binary black hole coalescence. And this means that at least for this type of system we start to make population studies so from nothing, we are now able to know the distribution of muscle. We have a black hole stellar mass black hole in binary system to have some indication from about their origin and evolution, and also some information about their spin. But the focus of the talk is I think in the case of city and gravitational wave we need to concentrate on the multi messenger and the symbol of multi messenger astrophysics is the gv 17 17 so I will give a brief overview of the results and what will be the future. So we received this gravitational signal from the gravitational signal was immediately evident that we were in front of something that was related to neutron star because one of the most important parameters that we are able to extract from the gravitational signal is the mass, and in particular in this plot you can see the component mass of the system, and these masses are completely consistent with the masses of the non neutron star in our galaxy. Another very important parameters that we can extract from the gravitational signal is the title the formability. So the title formability is important because it's directly connected to the amount of ejected mass, when the, the two neutrons that are close they are tidally disrupted so part of these masses the most that give rise to the electromagnetic emission, and in particular you can see here that with the gravitational wave we can start to constrain equation of state this line corresponded to a different equation of state. And in particular these are the other equation of state and these are the software equation of state so already with this signal, we were able to rule it out the most stiff equation of state. So this gravitational wave is a is a really promising way to see the interiors of neutron star. Then there was the fantastic detection of Fermi that was confirmed almost immediately by integral so this connection among binary neutron star merger and shorted GRB and from an observational point of view this object was exactly what we classified as shorted and then many many months of observation that show us something really very interesting and increase of the flux for many many months. And this increase of the flux for many many months in all the bands so radio optical index ray can be explained by two model. So by two scenario one, a mildly relativistic isotropic flow so a chock a jet in which we have a radial distribution of the velocity, but at the same time these increase of the flux can be explained also with a structure jet. So a jet faster in the faster in the center and slower in the border. So in which we were able to discriminate among these two scenario was using the radio observation and in particular the FBI because radio observation enable us to really look at the source with the right resolution. So we were able to constrain the size, less than two million second that means that these can rule it out the isotropic mildly relativistic outflow. So many many observations all the band plus radio enable us to say that which is 17 08 17 we were in front of a jet and the structure structure jet. So they are the thermal parts now, when you we have to neutral star they are titled is option we have an environment very rich of neutrons so a very high density of neutrons we have the right temperature for the nuclear synthesis of heavy elements, and in particular the same time we have also other component of the jet. For example, in the interface link to the creation is that power the jet in this part of the in this component of the ejected material, we have higher temperature so weak interaction, and we form elements but not so heavy, like the latencies or activities. And so what we expected was a blue component at the beginning for the component in which we have a higher weak interactions. And on the other side in the we expect we expected also a red component for the component in which we really can form heavy, a very heavy and what we observe was blue component in the first two days and the red component. And here you can see also the spectra the fantastic spectra that we took with the VLT shooter, and here in the there are the absorption feature that indicate exactly the presence of very heavy elements. So on the basis of what we know today about the major rate of neutron star and also the brightness of the source and also the evolution, we can say that binary just our merger can be is one of the major channel of formation of heavy elements in the universe. So gd 17708 17 was really crucial, because combining the gravitational wave and electromagnetic emission, we know better about the jet in, in jrb, and we know that there is this connection among gravitational wave and short jrb and so binary into a some major and short jrb. We know better about nuclear synthesis in the universe. At the same time, so we can also use the electromagnetic side to constrain the question of state so we can use both the messenger to constrain a question of state and no better about the radius of neutron star using the, when we identify the host galaxy, we can also use the rash shift of the galaxy, and the distance from the gravitational wave to estimate the constant now we have big error so we are not making cosmology with the precision of CMB, but with many of these observation, we can really start to make cosmology in a with a completely different way so we can also see what gravitational wave we see we say about the tension among CMB and supernova estimate of the constant. And we start also to know better what is the relation among the galaxy and the sources of gravitational waves so we start to understand better what is compact object formation and evolution. And now I go to another very interesting events that happened very recently, and I think this is very interesting because open a new scenario also for electromagnetic counter part of gravitational waves so before Christmas this year, there was a cheer B, and this is a journey from the point of view of the high energy is perfectly a long to be. So this is what observed with the Fermi, and this is the position of this to be in the harness ratio t 90 plot and you see that is exactly in the position of longer be is a minute duration to be as a long tail similar to the extended mission in the journey, but already if you look to the prompt and the bright spikes, they last more than 12 seconds. And this is the object that is close to is a 350 megaparsec and about 10 kiloparsec from the center of the galaxy. Why this object what is very interesting because if you look at the optical data in the position of the longer be there was a kilonova. Here you see the all the optical data collected, and in this paper, they, they, they show the, the best fit of the data with a kilonova emission. And in the dashed line you can see the kilonova observed for gv 17 08 17. And you can see that really these data reproduce well, so I really very similar to what was observed for gv 17 08 17 a bit more blue at the beginning and this is also consistent with the fact that this was observed on axis. And so the authors also examine it harder scenarios like supernovae but really kilonova seems to be a solid observational results. So these are putting challenge of the, the dichotomy that the, so the typical connection short long and different progenitors. So make more complex the classification scheme of Gervi, and in particular the authors were analyzing local Gervi and they say that about 10% of local long Gervi can be measure of binary on star, so that we have a contamination in the long Gervi of mergers so this is important because increase also the rate of joint detection that we can expect in the next years. So there is also another very interesting work about this object because they found a precursor and this precursor seems to show signature off for quasi periodic oscillation. And then results from a just a site group and also with colleague in enough. So what we discover was also a very interesting GV emission for these sources is a significant detection. And is a user can see here is a detection that start so we start to observe because in reality here is a perimeter is due to observational condition, but what we observe is this emission that lasts for about 10 to the second that start about six kilo second after the merger and last for a long time. So it's a late emission and here you can see all our best fit of all the data that we collected we have also radio data, and we also ask XMM data for which we have an upper limit and also for the radio. And here you can see the best fit of all our data in X ray and also the optical disease that taking into account the forward shock plus the in the optical band plus the key on our component. And what you see here is the Fermilat detection that we had, and you can see here that we have an excess. Here you can see the spectral distribution and while the the first point can be explained. Also with the forward shock so we can say that this is not the second point the red point is really very distant and so we can claim really a significant excess in the GV. And so we think that this is very interesting and to explain this excess with respect to the forward shock so that the synchrotron emission, the standard synchrotron emission that we use to explain the multi band observation for to be so to interpret these. This excess we can say that this excess can be explained by external inverse Compton, and in particular the seat photon can be the key of a photon and the electron cannot be the one of the relativistic jet that gives rise to the afterglow, because this is too much expanded to explain. A kilono a GB emission at 10 to the four seconds, so we need electrons that are more close to the kilonova photosphere. And so we need to invoke the presence of a low power jet that is emitted at late times that is not something that is not usually in GB so many features of GB are explained using the presence of these low power jet. Exactly that late times, I think that this is a very interesting. New detection, because it was not detected for GB 17 to 17 because this object was of axis, but it's very interesting because he's a new GB counterpart that I think is really interesting for family that but also for the future. I think it's a new concept like astro gamma or amigo because they will have also better sensitivity with respect to formula. So future gravitational with a strong now I go directly to the hero of Einstein telescope. And what I want to say okay Einstein telescope will be these these observatory triangular shape underground cryogenic was insert in in the history roadmap so he's in the priority of Europe and what means Einstein telescope with respect to today. What is important so first of all Einstein telescope will be a factor 10 better sensitivity at all frequency with respect to. So in the plot you can see here the sensitivity of like the Kagura and the ego that we expect 405 and is the most optimistic one. So a factor 10 at all frequency but also very important we will explore low frequency. So, going increasing the frequency and also going to lower frequency means that we can explore the early universe. So we can explore binary call up to the dark ages and why we need the low frequency because that when we observe gravitational wave the masses are shifted and so also what we observe now so 30 solar masses. When we go to the early universe their masses at low frequency so the signal is at low frequency so we really need the low frequency to explore the early universe. And what we will do with Einstein telescope is really population studies along the cosmic history so we can connect binary neutron star system of compact object with the star formation history the metallicity evolution of the universe. I give you the number to give you an idea. So here you can see the blue is the population of binary neutron star and the arrow of binary black hole coming out from population synthesis code that are able to reproduce what we observe today of binary neutron star and binary black hole. And we use a fish hermetic approach for the detection of of detection of gravitational signal we use a jewel fish that is a code that we developed and is publicly available. And what you can see here is that the number of detection will be huge so we will have 10 to the five binary neutron star detection prayer. And 10 to the five binary black hole detection prayer so the black hole that we observe today. And we will have the same amount or less up with the neutron star black hole so we really will have a huge number of events and a huge number of alerts for the astronomical community. And other important things so for the more close universe this fact that we will have a better sensitivity means that we will be able really to make an extra an extremely precise parameter estimation. So we can really start to talk about precise gravitational wave astronomy. And this is very, very important for example to study title deformability to study the interiors of neutron star. We will be able also to detect the post merger for gv 17 0x 17 we don't know from the gravitational wave if they are there was a remnant a black hole or a neutron star. We will be able to detect the post merger signal, and for sure up to 100 megaparsec we will be able to understand well what is the remnant. Another important thing is flooring low frequency means also that we can explore really intermediate massive let call and the merger of intermediate massive let call you can see here in this flow. And so in connection also with Lisa we can try to understand what is if really stellar muscle call are the seeds of massive let call and how these are connected with supermassive let call at the center of the galaxy. So going to the early university with the low frequency we will be able also to see the population of primordial the calls that we expect that increase that I have frequent at higher ratio. And so this is a very another very interesting astrophysical field that he can explore. So only few cases of the it is science cases but I think the most interesting one from the point of view of astrophysics. So for the cosmology what we love and is that we will have a lot of events like gv 17 0x 17 and so we can really start to talk about cosmology with gravitational wave and then we'll give you some numbers about this. And also we can really test the modified gravity at cosmological scale for example, testing the gravitational wave propagation and see if the distance coming from the electromagnetic signal is different from the distance that we can estimate from the gravitational multi messenger so all what we need for gv 17 0x 17 can be done with a larger sample of events and along the cosmic history and we can benefit a lot of the better parameter estimation. So really what show us gv 17 0x 17 is only only the beginning and in the ET here we will have a lot of science to be done with many, many events. And also we will have a higher chance to detect core collapse supernovae newborn neutron star so we can really have also many other sources of gravitational wave and electromagnetic counterpart. So for the multi messenger astronomy the first important information is sky localization. And so we did simulation and in particular ET is extremely interesting because as the frequency game with the low frequency. We can use the, the earth movement so we did a hard rotation so we long signal like the one for binary on star, we can localize only with ET also if it is observing alone. And we can detect about hundreds, we can have hundreds of detection per year with the sky localization, better than 100 square degree. And for this event we can have also the early warning I will come back later on this point of early warning. Okay, so if we have ET plus cosmic explorer the number of detection will be thousands with sky localization less than 110 square degree. And the situation is also better if we have ET plus two cosmic explorer because we can have 1000 of detection per year with sky localization less than one square degree. So you see how ET in a network of detector will be able to improve the sky localization. So for ET, it will be different with respect to today because we will have exactly to universe because for example Kilonova mission, taking into account also the sky localization of gravitational wave, we will not be able to detect a redshift larger than 0.3. And so to detect a counter part of it, larger reshift we really need the high energy. So close we will have Kilonova will benefit of a better parameter estimation. And if you want to go to the larger if you want if you want to have a counter part that larger reshift we need the high energy and so the gamma. So, now I will give you some number. And in particular, we did some simulation with the very moving observatory. If we use very moving in so in survey mode that we cannot do a lot for for Kilonova detection. But if we think about observation so asking the target of opportunity. If we look to all the objects that are detected with the sky localization less than 40 square degree. What we can have is that we can have a few tens of for join detection here using 10% of the data in telescope time. Now it's a huge number this 10% but I think that years from now is not so crazy idea to use 10% of the better moving observatory to follow up gravitation away because almost all the science goal of better will be rich. And so cosmology we can have really cosmology with a very good precision. High energy. So here I show you a work that was driven by one of my PhD students or some water on kidney is a comprehensive study in which we use prompt and after the mission, and we try to understand the perspectives of joint detection. And what we did was to take a binary neutron star population to normalize this population. And then we started to make a joint to estimate the joint detection. So if we take a gamma ray monitor and. We use them in survey mode what we can say is that almost all sure to be we live a gravitational wave. And so I think this is really very important. And in particular, we don't need to have about 70% of the data. We have a lot of data to make a joint to estimate the joint detection. So if we take gamma ray monitor and we use them in survey mode what we can say is that almost all sure to be we live a gravitational wave. And that's interesting because in future we will have really a multi messenger astronomy with a lot of senior. And in particular, we don't need to we have about 70% of joint detection with it plus cosmic exoplanet almost 100%. Then, depending on the satellite we will have 10 to 100 of detection per year and they show you for different detector what are our vision. And in particular here you see that there are some instrument that will give tens of detection and data that will give hundreds of detection. But I want to underline that will be extremely important to have the sky localization so the ones that have a small number but can give us the sky localization are crucial because are the these satellite that will give this sky localization then to drive the ground based follow up. Now I go on the afterglow on the X ray afterglow. Here we use the modeling that use the forward shot and they highlighted the mission. And we analyze the what happened in survey mode for different instruments so I send pro gamma TCU setup. And you can see that in survey mode already we can have tens of detection. And if we use a pointing mode so we select all the sources with the sky localization less than 100 scale degree, we point our, our telescope, we can have also in the case of 50 plus cosmic explorer also 100 of detection, but with some caveat. So first of all, we need to be in the source immediately because the afterglow is decreasing rapidly. And so we can lose a lot of detection, for example, if we are one hour later. And for our later is the number reduce a lot. And another important caveat is that what are the trigger to follow. So if we take all the object that have a good sky localization, the number is huge look at this. So if the number of sources with the sky localization less than 100 square degree are really a huge number. So this means what are the one that we needed to follow. So if we make a selection based on viewing angle and distance, this is also not enough to reduce so much the number of events. So one of the most important things will be on the basis of the sense case on the basis of the instrument, try to prior priority, okay, to make a prioritization of the trigger. So this will be crucial. And I think require a lot of work of the astronomical community together with the gravitational website from the gravitational website will be necessary to send more information with respect to today, and try to make a parameter estimation as fast as possible with very, very rapid update. So why are important wide field monitors first of all, because they increase the number of detections that we can have in the gamma ray. But if you look to this plot you can see that we can have a large increase of his gray object that are the one that are of axis so x ray will allow us a wide field monitoring x ray will allow us to really see objects that are more of axis so to understand better the jet in JV and also these are very important because I have a good sky localization so they can drive the ground based follow up and also send alert to more sensitive instrument like a Tina that is the only one that can then monitor the emission at a little time. So now I go in the last part of my talk on the synergies with the city. So we are we are starting some work on this. And I think all of these was, we are really more enthusiastic about the synergy after the magic and this detection of JV in very energy, in particular the detection of the of the very energy emission from the afterglow. And in particular I show you that with the Einstein telescope, we can try also to detect the prompt emission, not only the afterglow emission, because we can have as I told before pre alert so alert before the merger. And so we can use really early warning alerts from it. So it can give alerts and then we show you with what is this sky localization pre merger. And so what is some sense of CTA can follow off the gravitational wave signal. These are these work is driven by this a bit boundary that is one of my postdoc at the just aside. So, okay, if we take the binary intro star event up to a rash it equal to 1.5 that is more or less so what the CTA can see. We can see here, what is the sky localization pre merger. And in particular, the sky localization is here, here I show only 110 square degree we have all the sky localization our simulation the population is the same that we use for the work on high energy so x ray and gamma. And here what you see is the number of events per year that we can observe with sky localization less than 100 square degree and less than 10 square degree 15 minutes before the merger five minutes before the merger one and at the merger. And this is considering orientation but for the very high energy, we have the mission when the jet is pointing to us. So, here you can see the same table with the viewing angle less than 10 square degrees so on axis observation. Here you can see the number in this plot you can see the evolution of the, the number of detection per year as a function of the sky localization. So it's similar to the table but explore more sky localization in our simulation for ET plus cosmic explorer and ET alone. So, here the number that you see here for example one minute before the merger we have number that are not bad. But again there are some caveats so this number we don't know it priori what are the, the signal that are pointing to us. And so you look at the top of the plot and for example in this case in which we have 300 sources, we have 1000 of detection to follow up. And then there is another caveat that is also the city cycle. This is the gravitational wave will consider a cycle for the gravitational way but it's around 85%. But so this number reduce also because we, we need to use the cycle of CTA. But I think it's already very interesting because you can follow a lot, a lot of object because CTA will be very fast as a wide field of view. So it's really very, the perfect instrument to follow many, many of these, of these systems but another strategy can be, okay, we have a lot of detection. We make a, only one shot, we look at the probability of detecting sources. And if we take this type of strategy following all the sources with the sky localization let less than one square degree, one minutes before the merger with the only one single observation. We have the possibility to detect 20 very energy counterpart per year using 10% of the CTA time. So this is the number we have the plot and everything for different sky localization for many, many configuration of instrument, for example, ET also plus the current detector ET plus to cosmic explorers is also more the number also better with respect to this one. So then there is a detection or not depend really on the emitted energy of our source. But I think it's very promising in any case because we have from an observational point to view the capability to follow up many trigger and to detect sources. And again, if you look at these energies, and you compare with the energies of detection for that of the jury already detected by magic and death. I think that you can understand immediately that CTA will be really extremely interesting working with gravitational wave observatories. And so this is my last slide I hope to be in time. So I think that the future will be a revolution in our knowledge of early universe for mental physics but also astrophysics of transient instruments that CTA and ET can play really a crucial role in this scenario. So I want to thanks everyone and also I writing this in this slide the name of all the young people PhD and postdoc that are working on many of the results that I show you today.