Subject: Re: Sco X-1 with Jem-X



Dear Georg Weidenspointner

thank you for your very interesting email. I well remember your SCO X-1 data
because it so thoroughly confused our gain calibration software by contaminating
the calibration spectra. This only happened because the calibration sources
have become so weak after several years in space that source events overflowing
onto the calibration area were more numerous than calibration events
for our weakest calibration source. Improved software has been developed to
ease this problem. 

However, prior to the installation of this new software
several revolutions (all yours I'm afraid) were affected by poor automatic gain
calibration. This problem was resolved by using Instrument Characteristics
tables to provide the necessary gain history instead of the automatically
determined table. These tables were delivered to ISDC in September 2006, and
should be part of the characteristics tables delivered to you. The OSA scripts
that run the offline analysis are set up to look for these tables first before
using the archived versions of the automatically generated tables. So assuming
you have the correct IC package and the lastest OSA software, you should be
unaware of the difference.

Just for your information, the revolutions that need an IC table are: 410,
418, 419, 465 and 467.

However, the final test of gain correction performance is to look at the
position of the Xe line produced by the detector gas fluorescence. I try to
analyse all the publicly available data for this line, Science window by
science window and the results can be found at

http://spacecenter.dk/~oxborrow/sdast/GAINresults.html

Unfortunately, there was little or no public data to do this when I last looked
at these revolutions, so I will set this analysis running on your revolutions
tonight, and let you know the results as soon as possible. You can also look
for this line at 29.6 keV in the full detector, or background, spectra for each
of your science windows, however these are best seen in the context of a whole
revolution, for which 100 or more SCWs may be available, which is why I made
the website (above) as a service to observers.

Finally, I should add that the first 3 or 4 science windows of any
revolution are generally pretty dreadful where gain calibration is concerned.
The dreadfulness being directly proportional to the time elapsed since the unit
was last activated. Unfortunately this effect is getting worse and worse as the
instruments age. So I would advise you to steer clear of these early science
windows. Happily, most of your observations seem to be at the end of their
revolutions.

You are welcome to contact me about any aspect of the JEM-X calibration and
correction procedures.

Best wishes,

Carol Anne

DANISH NATIONAL SPACE CENTER
Dr. Carol Anne Oxborrow
Email: oxborrow@spacecenter.dk	Homepage: http://www.spacecenter.dk/~oxborrow
Telephone (direct): +45 35 32 57 33

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