Thermal components in the early X-ray afterglow of GRBs

Abstract

The possible presence of thermal components in the early X-ray afterglows of gamma-ray bursts is investigated. We discuss both the presence of a thermal continuum and, in particular, of collisional X-ray emission lines. We compute the predicted luminosity by a thin plasma for a range of metallicities for the continuum and the K_alpha lines of the elements Mg, Si, S, Ar, Ca and Fe. We show that light travel effects are dominant in the determination of the thermal continuum and line luminosities, and derive the relevant equations. We conclude that thermal lines and continua are unlikely to dominate the early afterglow of GRBs, unless the explosion site is surrounded by a very massive and extremely clumped shell of material. Such conditions are difficult to envisage in the close environment of GRB progenitor, unless they are excited by some strong precursor activity, like in the Supranova scenario.

Minor changes, A&A in press. Black and White printer friendly version available at http://www.ast.cam.ac.uk/~lazzati/thermal_bw.ps.gz

References in corpus (1)

• The X-ray afterglows of gamma-ray bursts GRB 001025A and GRB 010220 observed with XMM-Newton

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• Soft X-ray emission lines in the afterglow spectrum of GRB 011211:- a detailed XMM-Newton analysis
• On the Early Time X-ray Spectra of Swift Afterglows I: Evidence for Anomalous Soft X-ray Emission
• Swift and XMM observations of the dark GRB 050326
• Reconsidering the origin of the X-ray emission lines in GRB 011211