In Sherpa ARF and RMF energy grids do not have to be the same. The models are
specified on the energy grid supplied by ARF. During the convolution the model
predicted values are multiplied by ARF and integration is done over the RMF
energy grid. It is required that the ARF grid is always created at the
energy resolution of the RMF matrix or higher than the RMF energy resolution.
- Aneta Siemiginowska
> I can tell you what is happening in the XSPEC case and it looks as though
> Sherpa copied XSPEC here. The assumption I made is that you create an arf
> on energies supplied from an appropriate rmf file. The keyword in the arf
> then tracks which rmf file was used for the energies. If this keyword differs
> from the rmf read into XSPEC then there is a chance the user has made a
> mistake hence the warning message.
> What happens in psextract is that mkarf is run with the energies specified
> by the input string 0.1:11.0:0.01 (ie start at 0.1 keV go up to 11.0 keV in
> 0.01 keV steps) hence this gets written into the keyword in the arf. Now,
> psextract uses exactly the same energies to make the rmf so you are fine here.
> While we are on the subject here is my latest pet peeve. If you do run mkarf
> with the option to take the energies from the rmf you have to specify the
> following string 'grid(source.rmf[matrix][cols energ_lo,energ_hi])'. When
> I last checked this was wrong in the documentation. It also seems to be giant
> leap backwards in user-friendliness. mkarf ought to know enough to look in
> the correct columns in an rmf file.
> Keith Arnaud
> On Fri, Jan 12, 2001 at 09:39:14AM -0500, Casey Law wrote:
> > I've seen the second bug, regarding the arf file having 'RSPFILE' misset, in
> > my own work. The header RSPFILE is equal to '0.1:11.0:0.01', just as in your
> > data. In my case, I used Sherpa to work with the spectrum. After loading the
> > data 'data source.pi', Sherpa automatically looks for associated files with the
> > same base, 'source.rmf' and 'source.arf'. Although Sherpa give an error
> > message similar to XSPEC (since it can't fine '0.1:11.0:0.01') it loads the
> > 'source.rmf' file, and seems to use it properly.
> > I don't know the source of these numbers, but I'll be sure the psextract
> > developer gets this. Hopefully, we'll have another fix soon.
> > cheers,
> > casey
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