The evidence for X-ray line emission in GRB afterglows is
reviewed. Evidence from XMM-Newton observations of GRB afterglows has
showed moderate statistical significance soft X-ray lines in at least 3 GRB
afterglows, GRB 011211, GRB 030227 and GRB 040106. Blue-shifted soft X-ray
lines from Si, S, Ar were originally claimed in GRB 011211, which was
interpreted as emission from hot, outflowing gas around the GRB
progenitor, possibly originating from a supernova explosion. The
statistical significance of the line features. e.g. through Monte Carlo
simulations, will be addressed. Preliminary results from the afterglow
spectra provided by Swift XRT will also be presented. A small number of
these afterglows may show evidence for a soft X-ray excess, while a large
proportion show excess X-ray absorption. None of the afterglows appear to
show evidence for Fe line emission, in contrast with very early afterglow
spectra obtained by Beppo-SAX, ASCA and Chandra, but in agreement with the
XMM-Newton observations. The potential for detecting X-ray line features at
higher statistical significance will be discussed.
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