Date: Wed, 6 Jul 2005 18:29:57 +0200 (MEST) Subject: Interesting calibration results Dear All, I've been running the new version of j_calib_gain_fitting on all the available FRSS data, just to make sure it can handle every conceivable dodgy revolution (and it's taking an age!). However, I have discovered a very interesting effect. The figures below show the calibration source intensities for revolutions 16 to 25 for JEM-X1, and the Fe source peak channels for the same time interval. This is a good interval because there's so little grey-filtering, except in revolutions 17 and 18. The colour key for the points is: black, Anode 1 (Fe); red Anode 2 (Cd); blue Anode 3 (Fe); green Anode 4 (Cd). Channel values are given in raw PHA (onboard) channels. As you can see, the two Cd sources show a very slight but steady decrease in intensity as we expect from the decay of the calibration sources. But the Fe peaks show a strong gain dependancy in their intensities, both during the initial switch on decay and just after revolution 19 where the HV was stepped down. Here, a decrease in gain of just over 20% leads to a 25% drop in the strength of anode 1 peak and over 50% in anode 3. Clearly then, these peaks are strongly affected by the low level rejection criteria, and we can expect astrophysical Fe lines to be similarly affected. As we have pointed out to several enthusiastic users, using JEM-X for analysis of Fe lines (especially weak, oddly shaped lines) is a dangerous business. I will put these results on the Forum, and anyone doubting the truth of this statement can be directed there. Best wishes for a relaxing summer to all of you, 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 Date: Thu, 7 Jul 2005 17:30:19 +0200 (MEST) From: Carol Anne Oxborrow Subject: More on peak intensities To: pkretsch@rssd.esa.int, stefan@astro.su.se, silvia.martinez@uv.es., jerome, nl, sb, cbj, Stephane.Paltani@obs.unige.ch, njw Mime-Version: 1.0 Dear All, with a little more data now processed with the new version of j_calib_gain-fitting I can show you how the calibration source intensities look later in the mission. Carl has suggested that the strong affect seen in the earliest revolutions ( 16 -25, yesterday's email) was caused by the very restrictive rejection criteria that were originally used. Results from revolutions 170 to 216 (see attached figure) show that this is indeed the case. The black and blue data show fitted peak intensities for the Fe calibration spectra (6 keV, sources 1 and 3) and the red/green data points are for the Cd spectra (22 keV, source 2 and 4). Source 3 (blue) is most strongly affected, having a peak position at about PHA channels 80-85. The effect is seen both in the way the natural decay of the source is almost offset by the increasing gain of the detector, and intensity decreases where the HV setting is reduced. These effects however are tiny compared to those seen in the earliest revolutions. Source 1 at about PHA channel 110 shows a much smaller effect and the two Cd sources seem to show no effect of gain on their intensities at all. 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