0:27

Okay, so we restart DS9, go to Analysis>Virtual

Â observatory. Look at the primary MOOK.

Â Here's our set of possible observations. And let's

Â scroll down to obs ID

Â 1943, the wind and accretion disk in Cen X-3.

Â And now you can see what Cen X-3 looks like in Chandra.

Â It looks very, very peculiar, almost like a solar eclipse here.

Â That's because Cen X-3 is so bright, and we're using kind of a different

Â detector for this observation than for a lot of the other Chandra observations.

Â But our green regions are already set down here in order

Â to capture most of the photons that are present

Â or are coming from Cen X-3 into our

Â satellite. So let's now look at our light

Â curve. Let's first get our analysis programs

Â set up in the way we usually do.

Â 1:52

And we will look at our light curve just like we

Â did for the EXOSAT data. When

Â we click on Light Curve, our computer chugs

Â along and after a little bit of

Â time, here we go. Here's our

Â light curve. Also wildly varying up and down,

Â very similar to what it looked like in the EXOSAT observation.

Â Notice though, this is not as long an observation.

Â Okay, this is about 50,000 seconds.

Â 3:01

Now we're getting a little bit closer to seeing what's going on.

Â We'll zoom in again.

Â We left-click and

Â then release. And, oh, look at that!

Â Boom, boom, boom, boom, boom.

Â You can count the peaks here and count the amount of time.

Â And sure enough, it looks like it's about 4.8 seconds again.

Â But is it exactly? Let's go to our Power Spectrum and

Â find out. We click on the Power Spectrum

Â 3:42

and here it is: 0.2 seconds per, se-

Â se, 0.2 cycles per second. Let's zoom

Â in on it, left click, make our box here.

Â Here we go.

Â Do it again.

Â Left click and drag our box and there we have it.

Â Look at this! Our frequency for

Â our EXOSAT data was at about 0.207.

Â There's absolutely nothing in the Chandra observation at point 207.

Â It's moved! It's moved to 0.208 cycles per second.

Â 4:34

Look! The frequency is slightly different.

Â We get a doppler shift range just like we did before,but

Â now with Chandra, it is centered on 0.2080

Â seconds, instead of, 0.2071 seconds. So

Â f for Chandra, it is centered

Â on a frequency equal 0.2080

Â cycles per second, or a period

Â of about 4.81 seconds

Â instead of our frequency

Â with EXOSAT, which was about

Â 0.2071 cycles per

Â second, for a period with EXOSAT

Â of about 4.83 seconds.

Â There's a clear difference here. It's a small

Â amount, but look at the power spectra of

Â these two satellite observations side by side.

Â 6:48

What this means is Cen X-3 has spun up in 15 years; it's going faster.

Â And in fact, when you look at it over even longer time spans, it seems relentlessly

Â and predictably gaining speed in a more or less linear fashion.

Â What could be causing that? Well, it appears

Â that the companion star feeds the x-ray source some material, and as that

Â gas gets closer and closer to the neutron star, it gives the star a bit of a kick.

Â It's quite similar to what happens when an ice skater

Â does a spin and draws in his or her arms.

Â They spin faster and faster and faster

Â to conserve angular momentum. Pretty neat.

Â 7:45

One more interesting thing we can do is to

Â find out the luminosity of this object in the x-rays.

Â From the optical brightness and spectrum of Krzeminski's star, we have deduced that

Â the distance to Cen X-3 is about 20,000 light years.

Â Now, from the x-ray observations, we can find the average flux,

Â or the amount of energy that passes through each square

Â centimeter of our satellite's detector each second.

Â To do this, we return one last time to DS9

Â and examine Cen X-3's energy spectrum.

Â 8:32

We go to Analysis, and now we're going to do our Chau

Â Sherpa spectral fit. This is going to take all the photons

Â in the observation and fit it to a particular model of radiation.

Â There are lots of different models that you can try

Â to fit your data to, and in this situation, it's not

Â really all that important, because we just want to see the overall number,

Â an amount of radiation that's passing through our satellite

Â detectors independent of the actual way that it's actually radiating.

Â So we're going to choose the McAll data fit, or the McAll spectral fit.

Â But what we do want is to display the log, because we are going to be interested

Â in the flux, the amount of energy passing

Â through each square centimeter of our detector each second.

Â So we click on Display Sherpa logs.

Â And now we wait for our computer to do this analysis.

Â It's fitting hundreds and hundreds of thousands of photons

Â and it's going to take a little bit of time.

Â But here we are, and now you can see this is the plot of the energy output of

Â Cen X-3 superimposed with a little white line that's almost impossible to see.

Â We don't have to worry about that.

Â That's the actual model fit. What we're interested in is this

Â number near the top of our log. If our model choice

Â is more or less valid, we can use this flux to

Â predict the intrinsic luminosity of the object.

Â This is the flux that we would get from Cen X-3

Â if there was no absorbing gas and dust

Â between Cen X-3 and the Earth. This

Â is the number we want, it's about 2.4 times ten

Â to the minus nine ergs per centimeter squared per

Â second. The flux is 2.4 times 10 to

Â the minus 9 ergs per square centimetre per second.

Â This means that every square centimetre area at the distance

Â of the Earth from Cen X-3 receives about 2.4 times

Â 10 to the minus 9 ergs of x-rays

Â each second. If Cen X-3 radiates isotropically,

Â which is a highfalutin word for uniformly in all directions,

Â that means we can take this number and multiply it by 4

Â pi r squared to find out the luminosity of Cen

Â X-3, where r in this case is 20,000

Â light years, right? So, basically, what's happening

Â is here we are near the Earth. Here's Cen

Â X-3, and Cen X-3 is putting out light

Â 12:29

You can see that each second the light from Cen

Â X-3 will fill up a ball whose surface area

Â is 4 pi d squared. So all we

Â have to do is take the flux, which represents one

Â square centimeter of area and

Â multiply it by all of these other square centimeters

Â of which there are 4 pi r squared of them, where our satellite isn't.

Â But which if we did have something to detect Cen X-3, we

Â would see the same thing as we do here near the Earth.

Â 13:31

And if we do that, d is 20,000

Â light years. We multiply our flux

Â by the centimeter

Â equivalent of 20,000 light years, and if you do that, converting

Â light years to centimeters, you get the luminosity

Â of Cen X-3 is about 1.3

Â times 10 to the 37 ergs per second.

Â This is about 3000 times the entire

Â energy output of the Sun. And, all this from an object

Â whose radius is no bigger than half the length of Manhattan Island.

Â 14:29

So we've come full circle.

Â It appears that the precisely varying x rays we see in Cen x-3,

Â GK Per and other compact x-ray binaries

Â are rotation hotspots associated with the star's

Â magnetic field. Over the years we have discovered many

Â such sources, each with a unique set of orbital circumstances, and each with its

Â own characteristic idiosyncrasies. Indeed, we have just scratched the surface

Â of the wonderful world of x-ray binaries. And many

Â surprises were in store for astronomers over the past 40

Â years, and many more undoubtedly will come in the future.

Â But now it is time to move on, and explore an entirely different class

Â of objects. So stay tuned as we examine our

Â cosmic recycling centers, Supernova

Â remnants, which are the products of the

Â most dramatic and energetic explosions

Â that our universe has to offer.

Â