Modeling the iron line in GRB afterglows
The time and angle dependent yield of line and continuum
emission from a dense, metal enriched torus around a cosmological
gamma-ray burst (GRB) source is simulated, taking into account
photoionization, collisional ionization, recombination, and
electron heating and cooling due to various processes. The
importance of the hydrodynamical interaction of the GRB blast
wave with the torus as well as the fact that the photon spectrum
illuminating the torus material may strongly deviate from the
observed GRB radiation, are stressed. A model calculation to
reproduce the Fe Ka line emission observed in the X-ray
afterglow of GRB 970508 is attempted, but the results indicate
that even with > 0.1 M\odot of iron concentrated in a
highly metal-enriched region of R <~10-3 pc, as
estimated by other authors, it is unlikely that the observed
iron line luminosity is produced in this scenario.
File translated from TEX by TTH, version 2.32.
On 16 Jul 1999, 09:18.