Re: Exporting unabsorbed data points

On Mon, Apr 25, 2011 at 17:43 -0500, Fabien Grisé wrote:
> Hi all,
> 
> I have been using Isis and I have succeeded in doing most things I wanted to.
> 
> Doing some X-ray/UV/optical/IR fitting, I wanted to export unabsorbed
> fluxes of data and models. I have been able to export the fluxes from
> the models using eval_fun on a linear grid and then writing the values
> in a table with writecol.
> However, this may be obvious but I have not been able to export
> unabsorbed X-ray fluxes from the data (that I prefer to get in units
> of erg). I thought that fixing the nH to 0 would do the trick but
> apparently that does not work. Here is what I used:
> 
> load_par("fits/pldbb/pldbbsave");
> set_par("tbabs(1).nH",0,1,0,10000);
> set_par("tbabs(2).nH",0,1,0,10000);
> () = eval_counts;
> plot_unfold(1;dsym=-4,dcol=4,decol=4,mcol=2,power=0,res=2);
> write_plot("pldbb_total_dered";head=0);

For what it's worth, plot_unfold and write_plot are functions
contributed by Mike Nowak and are not part of the isis
distribution.

> 
> Is there another way to do this?
> Any help would be appreciated.
> 

To get the spectral model flux in units of photons/s/cm^2/bin
you can use get_model_flux like so:

  load_par("fits/pldbb/pldbbsave");
  set_par("tbabs(1).nH",0);
  set_par("tbabs(2).nH",0);
  () = eval_counts;

  f = _A(get_model_flux (1));

where the _A() function converts from a wavelength grid
(angstrom) an energy grid (keV).

To convert the model flux values from from photon flux to
energy flux, do:

  photon_energy = 0.5 * (f.bin_lo + f.bin_hi) * 1.e3 * Const_eV;
  f.value *= photon_energy;

At this point, the flux units of f.value are erg/sec/cm^2/bin
and the bin edges, f.bin_lo, f.bin_hi, are in keV.

To write these values with writecol:

  writecol ("filename.txt", f.bin_lo, f.bin_hi, f.value);
  
Thanks,
-John
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