Dear eROSITA helpdesk：
When I tried to use the tool srctool to extract the spectrum of some galaxy clusters, such as A3158 and A3266. The extracted ARF file sometimes has all zero values, I want to know what is the reason?
I hope you may help me. Thank you.
Best regards,
Peng
Some questions about ARF files
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JeremySanders
- Posts: 28
- Joined: Mon Jun 28, 2021 7:24 am
Re: Some questions about ARF files
Dear Peng
This could occur for a number of reasons. I suggest starting with a simple circular region and testing whether that works. Then you can move to a more complex extraction by adding more options.
Some problems might be due to
* Source model is zero over the extraction region - the default point source model is likely inappropriate for clusters. Try a large top hat model and disable PSF correction for testing. For more realistic extraction you likely need to provide an image file.
* xgrid parameter is not small enough (for small regions).
If you have a specific example, you could post it here.
Cheers
Jeremy
This could occur for a number of reasons. I suggest starting with a simple circular region and testing whether that works. Then you can move to a more complex extraction by adding more options.
Some problems might be due to
* Source model is zero over the extraction region - the default point source model is likely inappropriate for clusters. Try a large top hat model and disable PSF correction for testing. For more realistic extraction you likely need to provide an image file.
* xgrid parameter is not small enough (for small regions).
If you have a specific example, you could post it here.
Cheers
Jeremy
Re: Some questions about ARF files
Dear Jeremy
After I modify the parameters of srctool, I find that the default source type "POINT" is selected. After I change it to "GAUSSIAN", the correct ARF file is obtained. Beyond that, I think the "MAP" mode is probably better for working with extended sources, but I'm not sure how to generate mask.fits files in eSASS.
Thank you for your help!
Best regards,
Peng
After I modify the parameters of srctool, I find that the default source type "POINT" is selected. After I change it to "GAUSSIAN", the correct ARF file is obtained. Beyond that, I think the "MAP" mode is probably better for working with extended sources, but I'm not sure how to generate mask.fits files in eSASS.
Thank you for your help!
Best regards,
Peng
-
JeremySanders
- Posts: 28
- Joined: Mon Jun 28, 2021 7:24 am
Re: Some questions about ARF files
Dear Peng
You could create an image from evtool to use as the map. However, such an image is noisy and probably has background (perhaps smoothing could help). Alternatively, you can make your own model image. It's just a standard FITS image with WCS coordinates. It depends on your use case.
Note that the image is normalised automatically to 1 after loading. It should not contain negative values. If using a MAP, the PSF correction needs to be disabled.
Hope that helps
Jeremy
You could create an image from evtool to use as the map. However, such an image is noisy and probably has background (perhaps smoothing could help). Alternatively, you can make your own model image. It's just a standard FITS image with WCS coordinates. It depends on your use case.
Note that the image is normalised automatically to 1 after loading. It should not contain negative values. If using a MAP, the PSF correction needs to be disabled.
Hope that helps
Jeremy
Re: Some questions about ARF files
Thank you for your help, I have solved my problem.