X‐Ray Spectral Features from Gamma‐Ray Bursts: Predictions of Progenitor Models

We investigate the potentially observable prompt or delayed X-ray spectralfeatures from the currently popular gamma-ray burst (GRB) models. During theevolution of many GRB progenitors, a disk around the central GRB source isproduced. Shock heating as the GRB ejecta collide with the disk may produceobservable X-ray features. We first summarize predictions deduced from previouscalculations which invoke photoionization and relativistic blast waves. We thencalculate the quasi-thermal X-ray line features produced assuming the ejectaare nonrelativistic (which is more likely for the disk interactions of many GRBmodels). In the framework of the Hypernova/Collapsar model, delayed (a few days- several months after the GRB) bursts of line-dominated, thermal X-rayemission may be expected. The He-merger scenario predicts similar X-rayemission line bursts <~ a few days after the GRB. These X-ray signatures shouldbe observable with Chandra and XMM-Newton out to at least z ~ 1. Weak emissionline features <~ a few days after the GRB may also result from the supranovaGRB scenario. In all three cases, significant X-ray absorption features, inparticular during the prompt GRB phase, are expected. No significant X-rayspectral features might result from compact-object binary mergers.Comment: 20 pages, including 8 figures and 3 tables. Uses epsf.sty, rotate.sty. Final version, accepted for publication in to ApJ. Revised analytical estimate of maximum emission line luminosity. Numerical results and conclusions unchange