Education Activities To Accompany Chandra Data Analysis Software 3C273
Tiger, Tiger Burning Bright…
Now that we have a distance to this puzzling object, let's find out its true luminosity.
Loading 3C273
Start ds9, connect to the Chandra-Ed Archive by using the Virtual Observatory under the "Analysis" menu, connect to the Rutgers X-ray Analysis Server, and select the 3C273 image. (If you have forgotten how to do this, go to: http://chandra-ed.cfa.harvard.edu/learning_ds9.html for the instructions).
Note how different this source
appears from Cas-A! It appears to be much smaller, and there is a
little jet-like protrusion coming out from the lower right hand side of
the object. Also, the image shows a ring of emission that seems to be
black in the center. This is not really the way 3C273 is in the sky. It
is an artifact of the satellite and occurs because the object is so
bright in x-rays that Chandra's counters get saturated. We call this
phenomenon "pileup", and it is similar to overexposure in a
photographic image. But some x-rays are still there; they are just
spread out along a column of the detector. See if you can adjust the
contrast and brightness in DS9 to see the line of radiation. (If you
can't get a good look at this, select the "bb" color scheme, go to the
color menu, click on contrast/bias, and set the contrast to 1.5 and the
bias to 0.10).
Activity 3: Find the luminosity of 3C273
Enclose the image of 3C273 and
its jet within a circular region. We will be excluding some of the
"pile-up" photons, but we are just interested in an "order of
magnitude" estimate of the energy output from the object. Make a light
curve, using 1000 second bin widths, normalized by time. (I.e. in the
drop-down menu for light curve plots, enter 1000 in the box, and check
both the bin width and normalize by time options). When you get the
results, you should see a plot that has a y-axis value of about 1
count/sec.
What this means is that Chandra has received about one x-ray
each second from the region of the sky around 3C273.Since this is the
only strong source in the field of view of the satellite, we can say
that this represents roughly the x-ray energy received from 3C273 in
the energy band that Chandra is sensitive to. But think for a moment;
3C273 is pouring out these photons everywhere in the sky. Chandra only
picks up a very tiny percentage of them. The rest keep streaming out
into space, where no x-ray satellite is there to see them. In fact, we
can imagine a huge ball, centered at 3C273, whose radius is equal to
the distance from the source to the Earth. The tiny satellite's area
must be multiplied by the area of the ball (4πd2, where d= distance from 3C273 to the Earth) to get the amount of x-radiation that 3C273 is giving off into space.
It turns out that each count per second for the ACIS detector on board Chandra corresponds to about 10-11 erg/sec of energy crossing each cm2
of surface at the distance of the Earth. (Later on, we shall see a
simple way to determine this more accurately.) So what is the x-ray
output of 3C273?
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This is almost one trillion times the entire energy output of our Sun,
and 100 times the luminosity of our entire galaxy. Finding a mechanism
to produce this much energy would be difficult under any circumstances.
But the quasars present an even more difficult puzzle. These objects
fluctuate in brightness, and because of this, they must be rather
small.
To see why this is so, let us move onward [next] [back]
