On the Importance of On the Importance of Uncertainties in Response Uncertainties in Response

FunctionsFunctions

Martin C. WeisskopfStephen L. O’Dell & Allyn F. TennantNASA Marshall Space Flight Center

2010 April 142010 April 14 1

We consider two responses for We consider two responses for the Chandra HRMA/LETG/HRC-the Chandra HRMA/LETG/HRC-S.S.

• “Old” response is from 2003.• “New” response is from 2009

December. It includes a correction for higher orders.

• Changes are due to updates in the calibration of this spectrometer.

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Changes result in differences Changes result in differences less than (<5%) BUT …. less than (<5%) BUT ….

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The impact of these changes depends upon the spectrum.

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So you might think that nothing So you might think that nothing much happens.much happens.

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These parameters characterize These parameters characterize the first model.the first model.

• xsect = vern• abund = wilm• tbvarabs (NH and O free)• dust scattering (2004, ApJ 601,

1050) frozen @ 0.15 • powerlaw

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• Allowing for scattering by the interstellar dust is important• Impacts other parameters @10%

level

Note --- an important aside.Note --- an important aside.

Note --- an important aside.Note --- an important aside.

• I told you most of the relevant details of the model.

• This information is woefully missing in a substantial fraction of published papers.

• Verifying someone else’s results requires knowledge of these details. 8

We fit the pulsar’s spectrum to a We fit the pulsar’s spectrum to a powerlaw with the old response.powerlaw with the old response.

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We fit the pulsar’s spectrum to a We fit the pulsar’s spectrum to a powerlaw with the new responsepowerlaw with the new response

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Each response gives an Each response gives an acceptable fit to the data.acceptable fit to the data.

Parameter Old NewNH [1022 cm-2] 0.44 0.17 0.40 0.15O 0.67 0.08 0.78 0.09 1.63 0.02 1.64 0.02Norm [NE @ 1 keV]

0.51 0.09 0.49 0.09

2 () 1460 (1474)

1439 (1474)Errors are for 1 interesting parameter: 1 at

(2min +1).

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Note --- an important aside.Note --- an important aside.

• I told you all the relevant details of the fit.

• This information is missing in a substantial fraction of published papers.

• Believing the results requires knowledge of these details. Quoted errors for bad fits are generally underestimates.

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What happens when we add the What happens when we add the thermal component? thermal component?

Case Old New

Low-T limit 0.17 0.20

High-T limit 0.16 0.21

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Temperatures are 3- upper limits, in keV.

The seeming innocuous refinements The seeming innocuous refinements raised the 3raised the 3 upper limit by upper limit by 24%

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