MLI Correction page for NuSTAR SOC

What Is The MLI correction?

The MLI correction is provided as a tool to see if pathological observations not already corrected by the NuSTAR 20200429 CALDB release (and the subsequent CALDB and NuSTARDAS releases) .

There may be a subset of observations, in particular with bright sources, which may not entirely be corrected by the available CALDB. We have provided this mtable to be used in analysis for those observations. Care must be taken in applying this mtable as it may potentially skew the results if not used properly.

Extensive documentation of this issue may be found in Madsen, K.K., et al. (2020)   arXiv:2005.00569

This mtable model should not be used to force a model into agreement, but only if significant differences are observed between FPMA and FPMB.

The table below lists the observation sequenceID's where there MLI fraction is below 0.9 and where we recommend the use of the mtable model.

How Is It Used?

The MLI mtable correction is made available for pathological cases when there is a substantial difference between FPMA and FPMB. If these steps are not followed, and the mtable parameters and the constants between A and B are allowed to fit freely, incorrect estimates of the continuum and line shapes may occur.

1. First ignore FPMA between 3 and 7 keV, when doing your original fits. Make sure the model includes a constant offset between FPMA and FPMB. Find the value of the constant and freeze it.

2. Notice FPMA between 3 and 7 keV and add the mtable to the model. Set the fraction value of the MLI to 1.0 for FPMB and freeze it. Allow only the MLI fraction of FPMA to fit.

3. Please note: The range of MLI fraction should now lie between 0.9 and 1.0, and if the range is outside that, something else may be wrong.

Note: In some instances, the MLI correction may be too aggressive. This may be seen as the flux of FPMA being lower than FPMB between 3-5 keV, and the reason for this is that the change in MLI is gradual whereas the corrections are a step function.
In these cases one can revert to the old FPMA ARF. This can be done by running the keyword   inarffile=   in nuproducts and point it to   caldb/data/nustar/fpm/bcf/arf/nuA20100101v006.arf

Available MLI models:

The mtable model correction is recommended in analysis of the following observation sequenceID's

SequenceIDTarget NameDateMLI fraction

If you have any questions or comments about the NuSTAR clock correction file please use the HEASARC Help Desk, where you should select NuSTAR as the mailing list.

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