The signature of supernova ejecta in the X-ray afterglow of the γ-ray burst 011211

Abstract

Now that gamma-ray bursts (GRBs) have been determined to lie at cosmological distances, their isotropic burst energies are estimated to be as high as 1054 erg (ref. 2), making them the most energetic phenomena in the Universe. The nature of the progenitors responsible for the bursts remains, however, elusive. The favoured models range from the merger of two neutron stars in a binary system to the collapse of a massive star. Spectroscopic studies of the afterglow emission could reveal details of the environment of the burst, by indicating the elements present, the speed of the outflow and an estimate of the temperature. Here we report an X-ray spectrum of the afterglow of GRB011211, which shows emission lines of magnesium, silicon, sulphur, argon, calcium and possibly nickel, arising in metal-enriched material with an outflow velocity of the order of one-tenth the speed of light. These observations strongly favour models where a supernova explosion from a massive stellar progenitor precedes the burst event and is responsible for the outflowing matter.

New type of brightness variations of the colliding wind WO4 + O5((f)) binary WR 30a

“…WO stars have number abundance ratios (C+O)/He 0.62 (Kingsburgh et al 1995), initial masses M i > 40 M and WO-lifetimes of 27 000 yr to 62 000 yr, depending on initial mass and rotation on the main sequence (Meynet 2003, private communication). WO stars could very well be Gamma-Ray-Burst-associated supernova progenitors (e.g., Reeves et al 2002;Woosley et al 2002;Kaper 2003). Only three WO stars out of a total of 253 WR stars are known in the Galaxy: WR 30a (WO4+O5((f))) at d = 7.8 kpc, WR 102 (WO2) at d = 5.6 kpc, and WR 142 (WO2) at d = 1.0 kpc (van der Hucht 2001(van der Hucht , 2003, with terminal stellar wind velocities of, respectively, v ∞ = 4500, 4600, and 5500 km s −1 (Kingsburgh et al 1995), the largest wind velocities known among Population I WR stars.…”

Swift multi-wavelength observations of the bright flaring burst GRB 051117A

“…Indeed, there have been numerous claims in the literature for the detection of X-ray emission-lines in the X-ray spectra of GRB afterglows across a number of X-ray platforms including BeppoSax, Chandra and XMM (e.g. Piro et al 1999;Piro et al 2000;Yoshida et al 2001;Reeves et al 2002;Butler et al 2003;Watson et al 2003), though in the majority of cases the detection significance is modest (a few σ) at best. Line species identified include FeKα, with an energy consistent with the redshift of the host galaxies, and/or lines associated with blue-shifted lighter elements of S, Si, Ar, Mg and Ca.…”

“…Alternatively, the line emission may be formed by reprocessing of both the prompt and early afterglow emission at relatively large distances (R ∼ 10 16 cm, e.g. Reeves et al 2002;Kumar & Narayan 2003). In this scenario, the lifetime of the emission is determined by the size of the reprocessing region (see e.g.…”

GRB 010921: Strong Limits on an Underlying Supernova from theHubble Space Telescope

“…The presence of X-ray lines would require a significant amount of matter on stellar scales (e.g., Piro et al 2000), as may be expected in models involving the death of massive stars. However, to date, these detections (e.g., Piro et al 2000;Reeves et al 2002) have not been made with high significance.…”