Hello All,
I thought I'd mention that the next release of CIAO (v2.2, planned for the
fall), will likely include a new tool designed to deal with these events. The
tool will use a statistical method to identify 'out-of-time' events, and flag
them.
However, I'm wondering if this actually due to out-of-time events. Typically
one sees this effect for bright sources, but Vicky has said that the source is
rather faint. Another possibility is streaking, although this is more a
problem with the S4 chip. Vicky, you may want to look at the ahelp file for
'destreak', the tool for removing this instrumental effect.
There are also a number of caveats on the CIAO web page. Take a look at the
following, in case we've missed anything:
http://asc.harvard.edu/ciao/documents_datacaveats.html
casey
> >
> > Hello,
> >
> > I am wondering about the properties of possible trails along the readout
> > axis in ACIS images.
> >
> > The issue is that in an image we have found what appears to be a real
> > trail behind a point source, however it is along a column of S3, which is
> > the readout axis. We're wondering what the expected properties of
> > instrumental trails are so that we can compare with the data.
> >
> > The trail is behind a faint but very significant point source and we have
> > verified that it is not an aspect problem ie the events from the trail are
> > distributed evenly in time during our 20 ks observation.
> >
> > Vicky
> >
> > *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-
> > Victoria M. Kaspi
> > Associate Professor
> > McGill University
> > Physics Department
> > Rutherford Physics Building
> > 3600 University Street
> > Montreal, Quebec
> > Canada H3A 2T8
> >
> > Phone: 514-398-6412
> > Fax: 514-398-3733
> > URL: http://www.physics.mcgill.ca/~vkaspi
> > *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-
> >
> >
> >
>
> Vicky,
>
> Thanks for the question about the ACIS transfer streak. There's
> a description of the phenomenon in section 6.12.4 of the POG,
> which gives the crucial number: ACIS is read out at 40 microsec
> per pixel. The ratio of this number to the frame time for your
> observation (often 3.2 sec, but user-selectable) gives the ratio
> of the number of photons in the main image to those *per pixel*
> in the transfer streak. The streak should also, within errors,
> have a constant brightness vs. chipy.
>
>
> cheers,
> Dick Edgar
>
>
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