Minutes of the ASCA Calibration Workshop 6: Misc
Time assignment
Dr. Nagase (ISAS)We have found that, in GIS PH mode, there is a possibility to recover finer time resolution than previously thought. The ultimate resolution using standard bit assignment may be 3.90625 ms in High bit rate, rather than 62.5 ms as advertized (31.25 ms rather than 500 ms in M). We studied the time delay in on-board processing (to use this higher time resolution), and it is 10.7 ms on average with a +/-2 ms jitter, 8.5 ms of which is in the CPU, but there are some photons with a much greater delay.
- Dr. Ebisawa
- However, we should point out that when the telemetry is full, this cannot be achieved.
- Dr. Hirayama
- We will check on this using Crab data.
- Dr. Inoue
- What is the accuracy of previous missions using radio/X-ray comparison?
- Dr. Kawai
- Ginga also achieved 2 ms accuracy.
- Dr. White
- XTE will achieve a much higher accuracy, cross-calibration is possible.
Positional accuracy and the SIS source catalog
Dr. Gotthelf (GSFC)We have determined the positions of well-known X-ray sources from the SIS data, and found a systematic scatter with 0 offset and a 0.4 arcmin (Poissonian) mean. In fields with multiple SIS sources, we achieve 5 arcsec relative position, and attitude reconstruction is accurate to about 10 arcsec.
- Dr. Takahashi
- We see ROSAT vs ASCA shifts and SIS-0 to SIS-1 offsets.
- Dr. Gotthelf
- But ROSAT positions are typically only accurate to 20 arcsec.
- Dr. Gendreau
- Is radiation damage impacting on the star tracker CCDs?
- Dr. Fujimoto
- The duty scientist check, I don't think it's important.
- Dr. White
- Our plan for rev 2 reprocessing of the data is to apply the source detection algorithm developed by Dr. Gotthelf, and extract spectrum etc. This rev 2 will be our final archive.
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