Re: Rebinning to grid specified by psextract

Hi,

> When I extracted the pi spectrum using the psextract tool from CIAO,
> I specified a minimum number of counts per bin (following the
> example, 15). However, when I load the data into ISIS, it reverts
> back to the raw grid.
I have to admit that I don't know psextract, but on the ISIS side, it
might be that you have to set
    Isis_Use_PHA_Grouping = 1;
see
    help("load_data");
which contains the paragraph:
>> By default, isis ignores the GROUPING column of the input PHA file.
>> To automatically apply the grouping on input, set the intrinsic
>> variable Isis_Use_PHA_Grouping to a non-zero value.

[One may indeed wonder why it is set to zero by default... Is that some 
relic from former times?]

> How can I rebin the data so that it has at least 15 counts per bin
You can use
    rebin_data(id, 15);
for this task. If you want to do more sophisticated rebinning (i.e. to a 
certain S/N ratio, taking the background spectrum into account, too, or 
only rebin in a certain energy range), the mighty group function (that 
was only added with ISIS 1.5., iirc) can do the job, e.g.
    group(id; min_sn=4);

> and then rebin the ARF and RMF to match these grids,
I believe that using ISIS, you will not have to (worry about) 
rebin(ning) ARFs or RMFs, as this is done internally in memory.

Cheers,

Manfred
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