Cube slicing and and further analysis methods

[HealthyPear]

Data Analysis Question

Apologies if this has been already asked/answered I could not find a definitive answer.

Normally for extended sources one makes a "baseline" analysis down to even 100 MeV,
a "spectral"analysis which might start from higher energy and a "morphological" analysis, even higher in energy threshold.
Also, between spectral and morphological analysis there might be difference in the numbers of PSD components that one might want to use e.g. 0-3 for spectral, 1-3 for morpho.

What is the correct way (if possible) to make a single cube (the "baseline" cube), and then just "slice"this cube for the sub-cases?

Also, some methods like gta.tsmap accept keywords to restrict the energy range: is that possible also with gta.fit?

Right now I would think to:

1. create the baseline cube and run the baseline analysis
2. start the spectral analysis with the same config, but overriding keywords in GTAnalysis like selection/emin and selection/evt_type
3. now any roi created in this process will e.g. start from that emin so I do not need to overrid ts_map kwargs for that and any fit will be done considering only events from that emin

Am I right?

[HealthyPear]

and what about zmax? can I make a "big cube"with e.g. 105 and later use that cube with an analysis requiring 90 or in that case I need to make a dedicated new cube?

[omodei]

Hi @HealthyPear. I am not sure I understand your question. What "cube" are you talking about? If you are referring to the livetime cube (ltcube), that is the time that the LAT observed a given position on the sky at a given inclination angle, depends only on the history of the LAT's orientation during the observation and it does not depend on the energy. Nevertheless, if you change zmax, you'll have to recompute the ltcube as the field of view changes, hence the time each pixel in the sky is viewed. ltcubes can be summed, so you can combine ltcubes computed for sublime interval using the tool gtltsum

[omodei]

If you referring to gtexpcube (exposure cubes) I suppose that you could slice the exposure cubes, changing the keywords, but everything must be consistent. I would also recommend testing it and check that all the files are the same as the one obtaining specifying different emin/emax in the configuration file. Regarding gta.fit() it is called only after all the required products are calculated, so you cannot modify the energy range.