The Effect of Changes in theASCACalibration on the Fe K Lines in Active Galaxies
Author(s) -
T. Yaqoob,
U. Padmanabhan,
Tadayasu Dotani,
K. Nandra
Publication year - 2002
Publication title -
the astrophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.376
H-Index - 489
eISSN - 1538-4357
pISSN - 0004-637X
DOI - 10.1086/339166
Subject(s) - calibration , physics , line (geometry) , astrophysics , gaussian , galaxy , equivalent width , active galactic nucleus , emission spectrum , spectral line , astronomy , geometry , mathematics , quantum mechanics
The ASCA calibration has evolved considerably since launch and indeed, isstill evolving. There have been concerns in the literature that changes in theASCA calibration have resulted in the Fe-Kalpha lines in active galaxies (AGN)now being systematically narrower than was originally thought. If this weretrue, a large body of ASCA results would be impacted. In particular, it hasbeen claimed that the broad red wing (when present) of the Fe-Kalpha line hasbeen considerably weakened by changes in the ASCA calibration. We demonstrateexplicitly that changes in the ASCA calibration over a period of about eightyears have a negligible effect on the width, strength, or shape of theFe-Kalpha lines. The reduction in both width and equivalent width is only ~8%or less. We confirm this with simulations and individual sources, as well assample average profiles. The average profile for type 1 AGN is still verybroad, with the red wing extending down to ~4 keV. The reason for the claimed,apparently large, discrepancies is that in some sources the \fekalfa line iscomplex, and a single-Gaussian model, being an inadequate description of theline profile, picks up different portions of the profile with differentcalibration. Single-Gaussian fits do not therefore model all of the lineemission in some sources, in which case they do not compare old and currentcalibration since the models do not then describe the data.Comment: Accepted for publication in the Astrophysical Journal, Vol. 569, 10 April, 2002. 22 pages, 4 figure
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