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X-Ray Spectroscopic Measurements of Non-Equilibrium Ionization in Supernova Remnants

Published online by Cambridge University Press:  12 April 2016

T.H. Markert ,
C.R. Canizares ,
T. Pfafman ,
P. Vedder ,
P.F. Winkler  and
A. Pradhan
T.H. Markert
Affiliation:
MIT, Center for Space Research, Cambridge, MA 02139
C.R. Canizares
Affiliation:
MIT, Center for Space Research, Cambridge, MA 02139
T. Pfafman
Affiliation:
MIT, Center for Space Research, Cambridge, MA 02139
P. Vedder
Affiliation:
MIT, Center for Space Research, Cambridge, MA 02139
P.F. Winkler
Affiliation:
Dept. of Physics, Middlebury College, Middlebury, VT 05753
A. Pradhan
Affiliation:
JILA, University of Colorado, Boulder, CO 80309

Extract

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When a cool plasma is shock-heated to X-ray temperatures, the ionization structure does not attain its final, equilibrium value immmediately, but proceeds toward it through electron-ion collisions with a timescale τ ≡ net of order 1012 cm−3 sec. For supernova remnants (SNRs), where 0.1 ≤ ne ≤ 10 cm−3 typically, the time required to achieve collisional ionization equilibrium (CIE) can be greater than the age of the remnant. Even if the SNR is quite old, that part of the remnant which is emitting most of the X-rays may have been shocked relatively recently, so that the assumption of CIE may be inappropriate (see below).

The question of ionization equilibrium is of great astrophysical importance in the study of SNRs because it affects the deduced values of their masses and elemental abundances (e.g. Shull 1982). Mass determinations are affected because underionized plasma generally has a much higher emissivity in soft X-rays than equilibrium plasma. Unless this is accounted for, the deduced value of the density and therefore of the mass, will be considerably overestimated.

Type
Session 3. Non-Solar Astrophysics
Information
International Astronomical Union Colloquium , Volume 86: Eighth International Colloquium on Ultraviolet and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas , 1984 , pp. 76 - 79
Copyright
Copyright © Naval Research Laboratory 1984. Publication courtesy of the Naval Research Laboratory, Washington, DC.

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