Uh, thank you very much for the introduction and the invitation to come and speak here.
I always like to start off with a nice picture of one of the Veritas telescopes on something that wasn't our best observing night of the year,
obviously. But we did get a nice shot of the rainbow.
You can see at the top here, this is the MMT telescope.
It's the Whipple Observatory in Southern Arizona. And this is the facility I'll be speaking about mostly.
So I'm going to be talking about exploring the extreme universe with Veritas.
And we observe the extreme universe by studying in gamma rays.
This is a point in the talk where I always try to upset any astronomers in the audience by
telling you that gamma astronomy is by far the most important type of astronomy that there is,
and I can prove it. So the we typically gamma ray start at the rest mass of an electron.
So half an MLB and we can observe them now up to 100 TV.
So 10 to 100 TV gamma rays being produced in astrophysical objects.
And this we call all of this gamma ray astronomy. But you can see this covers an enormous range of the of the spectrum.
It's equivalent to shortwave radio, up to low energy X-rays.
And we tend to lump this all together into gamma ray astronomy that we have to use different techniques to cover different regions of this spectrum,
just as you do with with other parts of the electromagnetic spectrum.
I'm mostly going to be talking about Veritas, which operates from a few hundreds of well around 100 TV, up to about 30 TV.
We're looking for gamma rays. So you first have to think where they come from.
Gamma rays, of course, are only produced by non thermal processes.
There's no way you can get an object hot enough that it would emit gamma rays.
They're produced rather by processes such as inverse Compton scattering.
So this is where a high energy electron interacts with a lower energy photon and boost that photon up to two higher energies.
And this is a very efficient mechanism to produce high energy photons, gamma rays,
because the boosting factor is proportional to the Lorentz factor of the electrons squared.
So a 500 electron boost the energy of a photon by by ten to the 12, and an infrared photon can become a ten GeV gamma ray.
So this is a good mechanism to produce gamma rays.
If you have electrons, if you have hadrons protons, typically then you can produce gamma rays through the process of pion decay.
So what's happening here is a high energy proton hit some target material in stellar gas.
And what comes out is more protons and zeros.
At least that's one result of the interaction. And the PI zero decays immediately into two gamma rays.
And if you have high energy protons,
you'll produce high energy gamma rays for both of these processes to take place and to produce high energy gamma rays.
You need a population of relativistic particles.
You need a population of particles accelerated up very close to the speed of light.
So by looking at the universe in gamma rays, we're looking at the extreme universe,
places in the universe where there are acceleration processes taking place which are able to produce these very energetic particle populations.
We can produce the gamma rays through inverse Compton scattering or through pion decay.
Lower energy should have thermal emission from dust and from from stars,
or perhaps synchrotron radiation through accelerated electrons spiralling in magnetic fields.
But these are the high energy processes, the two that we're most interested in.
And one of the things we try to do with gamma ray astronomy is to distinguish between these two processes,
to discover whether the emission is due to electrons or due to hadrons being accelerated.
I'll talk more about that later. So how do we get these populations of accelerated particles on the earth?
You accelerate particles which shows Fermilab.
You accelerate particles by using electromagnets in tunnels and accelerating the particle particles around in that fashion,
in space, in the wider universe. There are lots of different.
Environments where particles can be accelerated. They can be accelerated in the jets produced by active galactic nuclei,
the supermassive black holes that lie at the heart of a good fraction of galaxies.
They can be accelerated in the shockwaves formed when a supernova takes place, when a star explodes.
Or they can be accelerated in regions of very intense electromagnetic fields, such as you'd find around pulsars.
So there's a variety of environments where you can accelerate particles and produce gamma rays.
And I'll talk more about some of those later. But I'd like to spend a little bit of time talking about how we detect the gamma rays.
And the most obvious thing you can do to detect a gamma ray is to send a gamma ray detector up into space,
which shows you the the large area telescope onboard the Fermi Gallery Space Telescope.
And this is basically just a big block of silicon with a particle tracker.
And it's been flying around the earth since 2008.
And what this does is it sits there. It's about one metre square, and it waits for a gamma ray to hit it.
The gamma ray pair produces produces an electron positron pair.
And by following the tracks of those two charged particles, you're able to reconstruct where the gamma ray came from.
And this is great. It works very well.
The problem is, if you want to go to high energies, so the LAT works very well up to ten, maybe up to a hundred TV.
But let's say you want to study gamma rays of one TV, which we know sources exist that can produce such high energy photons.
Then, for our strongest known gamma ray source in the TV region, you detect we have a flux of around six photons per square per year.
So if your detector is only one metre square large, you have to be very,
very patient or you have to come up with some mechanism to increase the effective area.
So you can either submit a grant proposal to NASA for $1,000,000,000,000 to build a bigger space telescope,
or you can try and do something a little cleverer. And what we do is to use the atmosphere itself as part of the detector.
And this allows us to increase the affected area at high energies.
So when when a gamma ray interacts in the atmosphere, it produces produce an electron positron pair.
And these can go on and through secondary power production and also brimstone processes.
You end up with what's called a particle cascade or an air shower coming down through the atmosphere.
This this shows you. So when you have an ash out in the atmosphere, the particle for one to be gamma ray,
the maximum number of particles occurs at an altitude of about ten kilometres.
You get some particles surviving below that altitude.
So the first obvious thing you can do is to try to detect those particles at ground level.
And that's what a number of experiments have done. The most recent one is called Hawk.
The High Altitude Water Cherenkov telescope. And this is it, I think four and a half thousand metres in Mexico at the peak of the recover.
And these are basically just large tanks of water, two metres tall.
And when a particle from a gamma ray cascade interacts inside the tank, it produces a flash of light.
And we're able to record gamma rays in that way.
So this is good. There are some downsides with this technique.
It's difficult to discriminate.
Gamma ray initiated showers from the background of showers initiated by cosmic ray particles hitting the top of the atmosphere,
which are much more numerous. You also have to build your detector up at four and a half thousand metres, which has some problems.
But this is quite effective. This works quite well. It doesn't work very well at relatively low energy.
So below. One TV for example. Simply because the particles don't make it all the way down to the ground.
So the alternative technique that we use is to use the cherenkov radiation.
So these charge particles are very high energy. They are moving faster than the speed of light in air.
You can't go faster than the speed of light in a vacuum, but you can go faster than the speed of light in air, which is see over the refractive index.
And all of these particles in the shower are moving faster than the speed of light in a when you do that,
if you have a particle moving rapidly through a transparent medium,
then the medium radiates and you end up with constructive interference and a wavefront of what's called cherenkov radiation.
And this is basically blue light. So the analogy here is with a sonic shockwave.
This is the the light equivalent of a sonic shock shockwave when an object moves faster than the speed of sound in a medium.
You can see cherenkov radiation around the core of a nuclear reactor, and you see a glowing blue light.
And this is also being produced by air showers in the night sky.
So this has been known for a very long time. Blackett in the late forties, early, early fifties,
did the calculation and realised that something like 1/10000 of all of the light from the night
sky is being caused by cherenkov radiation due to high energy particles in the atmosphere.
So he did the calculation and concluded There's no way you can observe this.
It's just too too small, in effect, to see Jelly.
And Galbraith took these numbers in one eye and thought about it and realised that the Cherenkov radiation would be there at such low levels,
but it would occur in very brief flashes associated with these particle cascades.
So in the early fifties, just 50 miles down the road in Harwell, they built the first Cherenkov telescope.
And it's very simple.
It's just a mirror and a photon multiply a tube, a light detector, and you plug that into an oscilloscope, and that's all you need.
You could go outside tonight and build one of these and it would work fine.
You'd see about one shower every every minute or so.
And this is essentially the same technique that we use today with our larger, more sophisticated telescopes.
The difficulty with just a single photon, multiple tube like this is that you can't record an image of the triangle of light.
Okay. You can just you can observe a flash, a drink of light, but you can't record an image of the shower in the cherenkov light.
But it's pretty easy. For that, you need a camera. And this is what people have been doing since the late eighties, is observing these shadows,
using an array of O2 multiplier tubes which make up a crude camera.
And the advantage of doing this is that it allows you to look at the properties of.
The image to reconstruct where the gamma ray came from and to discriminate the
gamma ray showers from this background of showers produced by cosmic rays,
by high energy particles.
So just to show you how that works when a gamma ray and because the atmosphere produces a particle cascade all the way through this cascade,
cherenkov radiation is being emitted and you end up with a pool of light on the ground with a radius of about 150 metres.
If you have a telescope lying inside that pool of light and you build a camera the focus of the telescope,
then you record an image which looks something like this fairly uniform and elliptical.
A cosmic ray shower would tend to have much more structure.
The electromagnetic development of the shower makes it fairly compact.
The the long axis of the shower here corresponds to the long axis of the ellipse.
And the point of origin of the gamma ray in the sky is going to be somewhere along this this dashed line.
So if you know, somewhere along that line,
you can break the degeneracy by building a couple more telescopes now such that they all sit within the same light pool.
And by intercepting these lines, you're able to say exactly where the gamma ray came from on the sky.
So in this way, you can start to do astronomy if you're having trouble picturing how that works.
Astronomers sometimes like to think of it in this way.
It's similar to the radiance formed by a meteor shower, and in this case, they all point back to the same position on the sky.
And this position is the direction of motion of the earth through to the tail of the comet or whatever.
That's what's causing the meteor shower. If you're not an astronomer, you can imagine yourself as Han Solo or Chewbacca.
And it's just exactly the same thing. The radiance of the things that are zooming past.
You point back to the air, the direction that you're travelling in or the direction the gamma ray came from in our case.
So the technique really came to life in the late eighties, early nineties, and that pushed the construction of a few new facilities.
Veritas is one I work on here in southern Arizona. There's also magic on La Palma in the Canary Islands, and Magic has two large 17 metre telescopes.
And then there's Hess down here in Namibia, which has four telescopes, about the same size as Veritas.
And then more recently, they added the largest string telescope in the world, which is a 28 metre diameter.
It's one of the largest optical telescopes in the world because remember,
while we use these for gamma ray astronomy, they're essentially optical telescopes collecting blue of light.
So the reason we were able to build 28 metre diameter dishes is that the mirrors don't need to be very good.
They don't need to be astronomical quality, so they're relatively cheap.
So Veritas is the instrument I work with. We constructed it in 2007.
We completed it. This is a nice picture taken from the hill behind the array.
It looks a little bit like it's been built in a parking lot,
and that's because we built it in a parking lot, and that was the only place we could find enough space.
You want the telescopes to be fairly well separated so that you can get a nice kind of stereoscopic view of the shower,
but they have to be within this local of a few hundred metres, so they have to be spread out by a hundred metres or so.
And this was the only place we had room to do that. This is the base camp to an astronomical observatory, the Whipple Observatory.
So the telescopes are actually relatively low altitude.
We put them down in the base camp a thousand metres because you don't need to be terribly high altitude for the type of cherenkov work that we do.
But this does mean we're the only astronomers in the world that sleep up at night,
up at the telescopes, and then drive down the mountain to observe every evening.
This is what the array looked like when we when we built it. We subsequently moved this telescope over here in 2009.
This was the original prototype telescope. And that was the only place we could put the.
Time we moved it over here to improve the array layout.
And this has turned out to be useful as well. I'll show you later on.
This just shows you the the spacing and the telescopes. And this has been built and operated by a collaboration mainly in the US,
but with come from contributions from Ireland, Canada and Germany and originally the UK.
There was a large group at Leeds which is where I came from, which doesn't exist anymore.
Just to tell you a little more about the telescopes. We have four of them.
Each telescope has a 12 metre diameter dish, so about 100 square metres of mirror area.
They're exposed to the to the environment.
So other than build a huge shed to cover the telescopes, we have a programme of continually retouching the mirrors.
It's like painting the fourth bridge. You just continually re coat the mirrors.
We have 100 spares that we take off and cycle back on, so each reflector gets completely refloated roughly once every two years.
And at the focus of each telescope we have a 500 pixel very, very crude camera, but it's very sensitive and it's very fast.
And so this is made up of focal multiplier tubes, which are very high gain, very rapid photo sensors.
And we spend our time this is this shows you to a series of images from each of the four cameras of the telescopes.
So these are maybe not the fastest movies in the world, but they're among the fastest.
Each frame in these in this movie is about two nanoseconds.
So you're watching basically a billion events per second frame right here.
And what you're seeing here are cosmic ray showers. So if you were able to resolve such short time scale phenomena with your eye,
you'd be able to go out on any evening, look up and you'd see these large showers.
This gives you the size of the full moon for comparison.
So these are degrees across and they'd be zipping around in the night sky.
These be recorded at a rate of about 500 per second, something like that.
And basically all of these events I'm showing you here a cosmic ray background events.
So while these are pretty to look at, these are the things we want to get rid of.
This is our background, the events we like to try and keep look more like this.
So this shows you a gamma ray event,
a nice uniform ellipse in each of the four telescopes and the long axis of the ellipse always points back to the same position in the camera.
So that tells you where the gamma ray came from on the sky. And it works very well.
We're able to pick out a gamma ray rate of just a few per minute from a background of hundreds per second thousandths per second.
In fact, we've even been able to by integrating over observations of hundreds of hours,
we're able to pick out gamma ray signals of less than a photon per hour, something like that.
So the technique works very well. We're able to reconstruct the position to within about a 10th of a degree, the size of the full moon.
And we can measure the energy of the shower's sorry, the energy of the incident gamma ray for anything above about 100 g.
And we observe every night of the year that we can for about 1400 hours in total.
It's maybe more instructive to show you what an observation looks like.
So if if you're running the telescopes at Veritas,
this is what you'd see if you observing the strongest steady gamma ray source in the sky, which is the Crab Nebula.
After one minute, we have a solid detection of the Crab Nebula.
These are background fluctuations. This is where the source is on the sky.
And this is already about five standard deviations above the background.
After a couple of minutes, it's even clearer and so on.
And once you get up to 5 minutes, you have ten standard deviations.
And that's the point on which you are able to measure the gamma ray spectrum of the source fairly accurately.
And with a very strong source like this, after a 30 minute observation,
you really start to see this horse come out very clearly against the background.
So the technique works. The crab was detected in 89 when we turned Veritas on.
The sky was still pretty much unexplored.
After we'd been running for a full 26, we detected only three objects the crab and two active galaxies Markarian 41 and Markarian 501.
After running for ten years now, we've managed to map out the sky a little better.
So this shows you a projection where the disk of our galaxy is along the equator here.
The shaded area shows you the region of the sky that we can see at high elevation.
And we've detected 56, I think now 56 sources.
But probably more interesting than the the number of sources that we've seen is the fact that they're not they're not all the same type of object.
So we've detected supernova remnants, pulsars, pulsars and nebulae, binary systems, radio galaxies, starburst galaxies and Blazars.
I'll tell you a little more about each of these.
But what this is really telling us is that particle acceleration can occur in lots of different environments in the universe.
There's a whole astronomy out there waiting for us to to look at and there's plenty of things to see.
So in 56 sources, I can't I can't cover everything.
So I like to try and pick out a few that I found find most interesting.
And to start with, the Crab Nebula itself and the the pulsar at the centre of the Crab Nebula is has historically
been very interesting and continues to be so we see steady emission from the crab,
as in the images I showed you earlier.
And this is believed to be caused by a relativistic wind from the pulsar wind
of electrons and positrons interacting with the environment around the pulsar.
These electrons and positrons get accelerated up to much higher energy, and then they inverse Compton,
boost photons up to gamma ray energies, and we can observe them in that way.
But this signal is steady and constant. What wasn't expected in the gamma ray region was to be able to observe a pulse signal.
So for those of you that aren't astronomers, a pulsar is a neutron star.
The half of a star that's exploded in non supernova, but they're typically rotating very rapidly.
So you can think of something the mass of the sun, the size of Oxford, spinning around like a kitchen blender.
And if there are emission regions on something that's spinning,
you get this lighthouse effect whereby if you're observing the emission region and that smaller than the rest of the object,
you'll see the beam of emission past your pass, your line of sight.
So the emission excuse me, so the emission that you observe in this case is going to be pulsed.
This has been seen across the spectrum for the crab, but prior to Veritas observations, it will always believed that the emission would cut off.
When you moved into the higher energy regime above about ten GeV, we decided to observe it nevertheless.
And what we saw is that this doesn't happen. The emission from the pulsar extends out to much higher energies.
With Veritas, we're able to detect emission above 120 gbps and there's a spectral point here all the way at 400 GMT,
where prior to this cut off was expected to occur around a few TV.
And this tells us initially that the the models for high energy emission from the crab pulsar were not were not quite correct.
Prior to these observations, most of the models suggested that the high energy emission was caused by curvature radiation,
which is where charged particles move along magnetic field lines close to the surface of the pulsar and produce gamma rays.
In that way, if this were true, then the high energy gamma rays that we do observe around a few hundred GeV would not be able to escape.
That's why you. Get this, the sharp cut off may be absorbed before they were able to escape the emission region.
The fact that we see higher energy gamma rays tells us there must be other processes taking place.
All the emission must be occurring very far out in the pulsar magnetosphere.
So this is not totally resolved. There are two or three different competing models which try to explain the higher energy emission from the pulsar.
So that was an interesting object to look at something I worked quite closely on myself with a gamma ray binary system.
What we now know to be a gamma ray binary system.
And this this story started back in 2007 with the discovery of a point like gamma ray source in the plane of the galaxy.
This was detected by my hats, and all I can really say about it was that it was a point source in the plane of the galaxy.
They didn't have any more information than that. We went and looked at it with Veritas over the next few years and we didn't detect it.
So we could either conclude that he was inventing results.
Veritas was broken or the source was variable.
We fairly confident that Veritas wasn't broken, so we we assumed that the source is variable.
We then went to look at it in X-rays and we saw a counterpart in X-rays to this gamma ray source.
And in X-rays it's also very variable. And by observing in X-rays over four or five years, we were able to observe a repeating period.
This shows you various different 315 days period overlaid on each other.
So the final piece in the puzzle, if you like, is to tie this repeating X-ray source to the camera emission.
And that's what we were able to do in 2012. We made observations very more intensively around the time of the X-ray peak,
and we see the gamma ray emission peaking at the the same phase of the period.
So we're fairly confident with this one now that it's a gamma ray binary system,
a situation something like this where you have a massive star in this case,
what's known as a B star, a star with ten or 15 times the mass of the sun with a Circumstellar disk around it.
And orbiting around this, you have a compact object.
So either a neutron star or possibly a black hole.
And as the compact object interacts with the material and with the photon fields around, the massive star gamma ray emission is produced in.
This gamma ray mission is modulated due to the geometry of the orbit and the changing environmental conditions.
So this is an object that we continue to study and the results get nicer and
there are various different models to describe this modulation and emission.
And these are these are nice objects to continue to study.
And we're hoping to get another one this year because there's a binary pulsar or a pulsar in a binary system like this just been identified,
which is believed to be on a 40 year orbit. Luckily, the very astronomers in November 2017,
so the time when the neutron star and the massive star are closest together, should hopefully occur later this year.
And we'll have a chance to observe this and see if we can see gamma radiation associated with it.
Another topic I've worked on quite a lot,
and one of the original motivations for for doing gamma astronomy is to discover the source of the cosmic rays.
So cosmic rays are a population of relativistic particles that fill our galaxy and their site of origin.
The place where they're being accelerated is still not completely clearly determined.
So cosmic rays were detected by Victor Hess back in 1912 when he took a gold leaf electric scope up in a balloon.
And he saw that this flux of ionising, what he called ionising radiation at the time, actually increased as you went up in altitude.
This tells you it's not terrestrial. It must be coming from space. Gamma rays can help to to understand where the cosmic rays are coming from.
Because they're neutral particles. They're produced in the same environment that the cosmic rays are being accelerated,
but they're neutral particles, and that means they travel straight from the site of origin to the earth.
Whereas the cosmic rays themselves are deflected by magnetic field.
So by the time they get to the earth, we've lost all of the information about where they came from.
So we look for the the sites of cosmic ray acceleration by studying the universe and gamma
rays in one place that's been proposed as the acceleration site is supernova remnants.
So this is the expanding blast waves of stars that have gone supernova.
And one object we've been looking at quite intensively is shown here.
This is ice four, four, three, which is also known as the jellyfish nebula, because apparently it's supposed to look like a jellyfish.
And this is the remains of a star that exploded somewhere between three and 30,000 years ago.
And it's quite a complex environment.
If you keep this picture in your head, you can see the star that caused the explosion would be somewhere in the centre here.
And you can see an expanding shell out to this side, a larger shell out to this side, and then a dark band cutting across the rim here.
And the way this is usually explained is that the smaller shell is expanding into a denser environment.
So it's expanding more more slowly. The larger shell is expanding into a more diffuse environment.
So it expands more rapidly.
And cutting across all of this and even through the remnant is a cloud of cold molecular gas which blocks the optical emission.
So we can't see it. But this dark cloud of molecular gas, much more dense than the ambient interstellar medium,
actually forms a really good target for accelerated cosmic rays to interact with and to produce gamma rays.
So while in the optical, the remnant looks like this nice and bright over here and over here with the dark band,
you might expect the gamma ray image to look almost like a negative of this.
So it would be brighter. But you have lots of target material for the cosmic rays to to interact with.
So we observed with their attacks that one and our latest images do indeed look pretty much like that.
We're now able to resolve all of the remnants if we place it on top of the optical picture here we see the brightest
parts of the emission here seems to be coming from the region where you have the densest amount of material.
And just to put this in context, this is the size of the full moon.
And if you were able to go out tonight for today and observe the sky with gamma rays,
this will be one of the brightest objects you'd be able to see sitting there resolved the remains of the star that exploded 10,000 years ago.
We see objects outside of our galaxy as well. And luckily, NASA's getting excited about these.
So they make nice movies for us.
And what's happening here is you have a supermassive black hole at the centre of an active galaxy which produces a jet of material.
And if that jet is directed the long line of sight, then we are able to see gamma ray emission associated with this.
And the gamma ray emission in this case can be very rapidly variable.
You can have something associated with the core of a galaxy that's varying on timescales of minutes or seconds.
These are most common source classes that we observe.
They can be very bright, much brighter than the crab, for example, which is the brightest steady source on the sky.
These can reach fluxes of five or ten times the crab.
We see active galaxies if they're close and they have a jet.
But the jet is misaligned with our line of sight. So the jet doesn't necessarily have to be pointing towards us.
If the if the galaxy is very close, then we can see gamma ray emission also associated with these objects.
These are interesting because if you're able to resolve because the galaxies are close,
you're able to resolve the jet in X-rays and radio and possibly try to correlate changes in structure of the jet with the flux of gamma ray emission.
So we can't actually resolve a galaxy and its jets and gamma rays or angular resolution is not good enough.
But we are able to correlate the integrated flux of galaxies with the structure seen in other wavelengths,
and we can observe starburst galaxies as well outside of our own galaxy.
These are galaxies like our own. But with maybe 30 times the rate of supernova explosions producing many more cosmic rays in a denser environment,
so they just glow generally in gamma rays.
I think I'll skip that because I'm getting a little slow, a little short on time, and I'd like to leave a few minutes to talk about the future.
So what Veritas and Hess and Magic of have all shown us is that there's plenty of things to look at.
There's lots of environments where particle acceleration takes place and there's a whole astronomy out there waiting to be done.
The Veritas catalogue has about 56 sources.
The entire catalogue for the gamma ray sky at these energies is only about 150 sources.
So there's very likely much a lot of stuff there that we just haven't had the sensitivity to observe yet.
So what we need is a better telescope. And this is where the Cherenkov telescope array comes in, which Garrett and myself are both working on.
And CTI is planned to be a large telescope array using exactly the same technique and methodologies, Veritas and the others.
But on a much larger scale. You can see a mock up of the array here.
And the idea is one difference you'll see with Veritas is that we have telescopes of different sizes.
So here we have four large telescopes.
These are planned to be about 23 metres in diameter, surrounded by a cluster of 20 to 25 medium sized telescopes about the size of Veritas,
12 metres in diameter, and then a wider, more spread out array of smaller telescopes, each with about four metres diameter.
And the idea here is to expand the dynamic range of your observations.
As I mentioned at the start, gamma rays cover an enormous range of the electromagnetic spectrum.
And with a design like this, you're able to use the large telescopes to target lower energies below 100 GeV.
The medium sized telescopes target energies around one TV, and then the larger telescopes spread out over a much larger area.
Because the flux of gamma rays is so low at the highest energies, they're able to give you sensitivity up in the 10 to 100 TV regime.
So Ccta, with a much larger number of telescopes and three different sizes of telescopes,
should be able to give you a much larger range and a factor of ten sensitivity improvement on the on the current detectors.
It's planned to be two observatories, one in the south.
The site's been set to be in Chile of the European Southern Observatory and one in the north, which is going to be in La Palma.
So this is all under development at the moment.
The telescope designs are being put together.
You have the large telescopes, the medium sized telescopes and the small telescopes, and there are different ideas about the best way to build these.
And one particular new idea that's being implemented is the idea of using a dual mirror system.
And there are a few different advantages to this.
One of the main ones is that you're able to reduce the size of your camera package and that allows you to fit.
I'll show you a picture at the end that shows you what that allows to do.
So coming back to Veritas, if you remember, we moved one telescope from here over here.
So this gives us a nice empty pad there to build a new prototype on for the the CTI experiment.
And that's what we're doing. This is a mock-up of it, but this is a photograph taken yesterday.
And you can see we have the structure built of one of these medium sized dual mirror telescopes.
So the mirrors on yet when they're on, this is going to be nine metres diameter.
They'll be a secondary mirror here and the camera will be hidden behind the mirror with the light reflecting back onto it.
So we're quite excited about this, unfortunately. Garrett and Andrea, his student,
and the rest of the group beat us to it a little bit because they managed to build a dual mirror telescope before we did.
And this shows you the Gamma Ray Cherenkov telescope, which they constructed, which is a design for one of the small size telescopes of CTI.
So this is four metre diameter in total, but with a dual mirror system.
And here you see the camera, the the focus of the secondary mirror.
So this was inaugurated in Paris earlier this year, I guess, and operating in Paris,
which is not the best observing place in the world on the full moon.
They were able to record first light and this shows you the cherenkov image of a cosmic ray shower detected using a dual mirror telescope system.
And here you can see the Veritas field of view on this camera would be about this big something like this.
So the advantage of this dual mirror system is that it gives you a much larger field of view with much finer pixelation.
So you get much, much better images, much more information in the images, and you're able to cover more of the sky less expensively as well.
So I'll finish there. High energy gamma rays providing us a new view to the extreme universe.
We know the technique works from the current generation of instruments,
and the very first results already allow us to do lots of interesting astrophysics.
But CTA is coming and is going to improve things.
And just as a taster, this is a simulation of the plane of our galaxy with a zoom on the inner 20 degrees or so,
showing you the kind of angular resolution you can expect to get and the sheer number and variety of sources that you might expect to be able to see.
Scott Then you got any questions?