Re: using fakeit

Hi,

>> 1.) when i use fakeit (with a  function and parameters that I already used to 
>> fit data) nothing comes out. I just get a straight line. I'll put the code 
>> below:
>> 
>> load_arf("/export/lecanard/6601/combined/6601_HEG_1.arf");
>> load_rmf("/export/lecanard/6601/rmf/acis_1.0_HEG_-1_rmf.fits");
>> assign_rmf(1,1);
>> assign_arf(1,1);
>> 
>> require("xspec");
>> fit_fun("phabs(1)*pcfabs(2)*diskbb(3)");
>> 
>> set_par("phabs(1)", [2.683428 ]);
>> set_par("pcfabs(2)",[2.711441 ,0.6840924]);
>> set_par("diskbb(3)",[52.20151 ,1.897251]);
>> 
>> fakeit;

I assume the exposure defined by the ARF is long enough that you would 
get at least one count (with a reasonable Poissonian probability)?
You can set this exposure with
    set_arf_exposure(1, exposure);


>> 2.) Eventually what I would like to do is just take the model that I had
>> before and extend it to cover wavelengths that my data can't see...(up to
>> about 25 keV).  However, if I put in an arf I'll just be cutting the effective
>> area away to match what I already have. Can fakeit do this or should I look
>> for other avenues?
> 
> If you just want to evaluate the model, you can use eval_fun
> and provide an arbitrary grid:
>    (lo, hi) = linear_grid (ylo, yhi, num_bins);
>    f = eval_fun (lo, hi);

I.e., you have to distinguish between counts and flux space.

Extending the grid in counts space doesn't make sense to me, as the 
counts are measured by the detector, which usually cannot be extended, 
unfortunately. In order to describe the detector, you need ARF and RMF.

The code John describes gives you the source flux in photons/s/cm^2/bin 
defined by your model and independent of any detector.

Cheers,

Manfred
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