Subject: Re: broad emission-like line feature in the JEM-X spectra (helpdesk#10467)


Dear Peter and Kate,

I've been talking to Soeren Brandt again about this strange feature that may
be an Fe line. He explained something that I'd misunderstood before, namely
that the problem around 5-7keV is not just the low energy cut off, but that
there is a transition region in the rejection criteria that occurs between
quite definite ADC (onboard energy channels) channel values, but that when
corrected/calibrated to KeV values, change with the gain of the instrument.
This means that the instrument sensitivity is calibrated at 6 months intervals
using the Crab, with gain at some particular value, so that the transition
bump occurs one place, and then as soon as the gain changes this bump moves
along a little, and the data is still processed with the bump found in the
calibration and so little dips and peaks will crop up in the processed spectrum.
This is a very insidiuous problem that will always make it difficult to analyse
Fe lines with JEM-X, except for the cases of a very strong Fe line.

It will be interesting to re-analyse the data with the OSA software, including
the differential gain drift, but this will not necessarily help us determine
whether this is Fe or just and instrumental artifact.

Best wishes,

Carol Anne




DANISH NATIONAL SPACE CENTER
Dr. Carol Anne Oxborrow
Email: oxborrow@dnsc.dk	Homepage: http://www.dsri.dk/~oxborrow
Telephone (direct): +45 35 32 57 33
Telephone (secretary): +45 35 32 57 01
Fax: +45 35 36 24 75

-------------------

The Danish National Space Center (DNSC) is a new research center under the
Ministry of Science, Technology and Innovation. The center is the result
of the Danish Space Research Institute merging with a part of the National
Survey and Cadastre.

Read more about the Danish National Space Center at: www.spacecenter.dk
E-mail: office@spacecenter.dk