X-ray spectral features from gamma-ray bursts:: Predictions of progenitor models

We investigate the potentially observable prompt or delayed X-ray spectral features from the currently popular gamma-ray burst (GRB) models. During the evolution of many GRB progenitors, a disk around the central GRB source is produced. Shock heating as the GRB ejecta collide with the disk may produce observable X-ray features. We first summarize predictions deduced from previous calculations that invoke photoionization and relativistic blast waves. We then calculate the quasi-thermal X-ray line features produced assuming the ejecta are nonrelativistic (which is more likely for the disk interactions of many GRB models). In the framework of the hypernova/collapsar model, delayed (a few days to several months after the GRB) bursts of line-dominated, thermal X-ray emission may be expected. The Hemerger scenario predicts similar X-ray emission-line bursts less than or similar to a few days after the GRB. These X-ray signatures should be observable with Chandra and XMM-Newton out to at least z similar to 1. Weak emission-line features less than or similar to a few days after the GRB may also result from the "supranova" GRB scenario. In all three cases, significant X-ray absorption features, in particular during the prompt GRB phase, are expected. No significant X-ray spectral features should result from compact-object binary mergers.