Effect of Changes in the ASCA Calibration on Spectral Parameters
(ASCA GOF Calibration Memo [ASCA-CAL-01-06-18, v1.0: T. Yaqoob, U. Padmanabhan, T. Dotani, Y. Tanaka, & the ASCATEAM])
The ASCA calibration has evolved considerably since launch, and indeed is still evolving, with a new (and final) release planned for the end of 2001. In this memo we summarize major changes in the ASCA calibration since launch and address how these changes affect spectral parameters derived from fitting models to real, inflight data. In particular, there have been concerns in the literature that changes in the ASCA calibration have resulted in the Fe-K lines in AGN now being narrower than was originally thought, based on older calibration. We show that this is not the case.
We have characterized the changes in deduced spectral parameters obtained from spectral fitting ASCA data with two sets of calibrations (OLD and CURRENT), for typical power-law and optically-thin thermal continnua, and for the iron K lines in AGN. The changes in the ASCA calibration over more than eight years since launch do not have a significant effect on continuum shape, absorbing column density, or the the iron K lines in AGN. This is notwithstanding degradation in the SIS low-energy efficiency, which has not yet been incoorporated into the ASCA calibration.
We find that the width and strength of the iron K lines in AGN has not been affected by changes in the ASCA calibration. That the calibration updates have not resulted in altering the width of the lines is not surprising since there have been no time-independent changes to the calibration which affect the energy resolution of any of the instruments.
This file was last modified on Wednesday, 01-May-2002 13:43:47 EDT
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