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Examine Plot Closer

When you answered the questions on the previous page, did you find that the model looked pretty good? Overall, it looks like the model fits the data fairly closely. However, when you look closer at the plot, you might find areas where the model is not quite as good as it seemed at first. To see if there are any "problem" areas, you should change the x-axis of the plot to zoom in on the plot.

Recall that the command easydata allows you to change the endpoints of the x-axis. So, start by looking at an x-axis of 0.5 to 2.0 keV:

easydata 0.5 2.0

Plot showing the powerlaw + blackbody model (black line) and the data
	(red line) between 0.5 and 2 keV

Plot showing the powerlaw + blackbody model (black line) and the data (red line) between 0.5 and 2.0 keV.

Answer the following questions for the 0.5-2.0 keV detail plot (it might be helpful to print the plot, if you can; click here if you need instructions on printing the graph.)

  • How well does the data and model match for the 0.5-2.0 keV region?
  • Are there any places where the data (in red) seems to diverge from the model (in black)? If you have printed the plot, indicate on the plot where this region is.
  • Does the model diverge very much here? Does it seem to diverge in a pattern? Or does it seem to be a "random" divergence?

Let's look at the answers to those questions for 0.5-2 keV. Also refer to the image below the answers.

  • How well does the data and model match for the 0.5-2 keV region?
    Overall the model and data seem to match pretty well for this region. There are a couple places where there might be some divergence between them.
  • Are there any places where the data (in red) seems to diverge from the model (in black)? If you have printed the plot, indicate on the plot where this region is.
    The lower energy part of the plot looks pretty good; however, there's a bit of divergence just before the "bump" around 1.6 keV, and there are a couple of data points well off the plot on the other side of the "bump". (See plot below)
  • Does the model diverge very much here? Does it seem to diverge in a pattern? Or does it seem to be a "random" divergence?
    The lower energy parts of the data seem to have some random scatter around the model. The part just before the bump at 1.6 keV seems to all fall below the plot in a smooth curve. The two data points on the higher-energy side of the bump seem random.
Plot showing the powerlaw + blackbody model (black line) and the data
	(red line) between 0.5 and 2 keV with some explanation of how
	well the model fits.

Plot showing the powerlaw + blackbody model (black line) and the data (red line) between 0.5 and 2 keV with some explanation of how well the model fits.

Repeat "slicing" the plot, and answer questions about each slice

Re-plot the data and model using easyplot to look at the following slices of the plot:

  • 2.0-4.0 keV
  • 4.0-6.0 keV
  • 6.0-8.0 keV
  • 8.0-10.0 keV

For each "slice", answer the following questions:

  • How well does the data and model match for this region?
  • Are there any places where the data (in red) seems to diverge from the model (in black)? If you have printed the plot, indicate on the plot where this region is.
  • Does the model diverge very much here? Does it seem to diverge in a pattern? Or does it seem to be a "random" divergence?

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Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Project Leader: Dr. Barbara Mattson
Curator: Meredith Gibb
Responsible NASA Official: Phil Newman
All material on this site has been created and updated between 1997-2014.
This page last updated: Thursday, 25-Mar-2010 09:08:34 EDT