Fe K Emission from X-ray Reflection: Predictions for
Gamma-Ray Burst Models
D.R. Ballantyne & E. Ramirez-Ruiz (Institute of Astronomy, University of Cambridge, U.K.),
Abstract
The recent discovery of Fe K
line features in the X-ray
afterglows of several
-ray bursts (GRBs), particularly the
Chandra observation of GRB 991216, may provide important
constraints on the immediate environment of the burst and hence on
progenitor models. The large Fe K
equivalent widths inferred
from the X-ray observations favor models in which the line is produced
when the primary X-ray emission from the source strikes Thomson-thick
material and Compton scatters into our line of sight. We
present such reflection spectra here, computed in a fully
self-consistent manner, and discuss the range of ionization parameters
that may be relevant to different models of GRBs. We argue that the
presence of a strong hydrogen-like K
line is unlikely because
Fe XXVI photons are likely to be resonantly trapped and removed
from the line core by Compton scattering. In contrast, a strong narrow
emission line from He-like Fe XXV is prominent in the model
spectra. We briefly discuss how these constraints may affect the line
energy determination in GRB 991216.
CATEGORY: SOLAR SYSTEM AND MISC