Hi Sandy,
Almost, but not quite. BACKSCAL is 2.99679E-06.
Dave.
> Hi Dave,
>
> It looks like the total detector area is defined* to be 8192 x 8192
> pix^2 (2^13=8192). If you look at the *evt2.fits in ds9 and block by 64
> and then zoom as needed you can convince yourself this is the case.
>
> So now we have ...
>
> calc '8*8*pi/(8192 * 8192) '
> = 2.99606e-06
>
> calc '2.99606e-06*10.66'
> 3.1938e-05
>
> Is 2.99606e-06 the value you are getting for BACKSCAL?
> I checked another case and it looks like this is how BASCSCAL is defined
> if you extract from the raw events list.
>
> *I have no idea why, other than to fit the entire I and S
> array into these dimensions with either I or S aimpoint on center
>
> Hope this helps-
> Sandy Patel.
>
>
>
> -----------------------------
> Sandeep K. Patel
> UAH/NASA-MSFC SD50
> X-ray Astrophysics Branch
> W: (256) 544-3965
> patels@dante.msfc.nasa.gov
>
> On Thu, 31 Aug 2000, Dave Smith wrote:
>
> > Hi,
> >
> > I have extracted spectra using dmextract and a source region file, and
> > wish to know how the BACKSCAL parameter is derived in the resulting
> > spectral file. My understanding is that the BACKSCAL parameter is the
> > area of the region divided by the total area of the detector. So, for a
> > circle of radius 8 pixels,
> >
> > BACKSCAL = 8^2 * pi / ( 6 * 1024^2 ) = 3.19E-5 (ACIS-S configuration).
> >
> > This is a factor 10.66 larger than the actual BACKSCAL keyword value. Is
> > there something I have misuderstood?
> >
> > Dave.
> >
> >
>
>
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