GRB 021004 modelled by multiple energy injections

Abstract

GRB 021004 is one of the best sampled gamma-ray bursts (GRB) to date, although the nature of its light curve is still being debated. Here we present 107 new optical, near-infrared (NIR) and millimetre observations, ranging from 2 h to more than a year after the burst. Fitting the multiband data to a model based on multiple energy injections suggests that at least 7 refreshed shocks took place during the evolution of the afterglow, implying a total energy release (collimated within an angle of 1.• 8) of ∼8 × 10 51 erg. Analysis of the late photometry reveals that the GRB 021004 host is a low extinction (A V ∼ 0.1) starburst galaxy with M B −22.0.

GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy

“…The host galaxy is a prolifically star-forming galaxy at a systemic redshift z = 2.3304, which has a SFR of ∼40 M yr −1 as also found by Fynbo et al (2005) and de Ugarte Postigo et al (2005), reinforcing the potential association of some GRB with starburst galaxies (Christensen et al 2004;Gorosabel et al 2005, and references there in).…”

“…From the total measured Lyα intensity (Castro-Tirado et al 2002), we derive a Lyα luminosity L Lyα ≤ (9 ± 1) × 10 42 erg s −1 , which implies a SFR ≤ 10 M yr −1 in agreement with Fynbo et al (2005) and Jakobsson et al (2005). The Lyα/Hα ratio of 2 implies a low dust content in the GRB host galaxy, as also inferred by de Ugarte Postigo et al (2005) and Kann et al (2006) from the afterglow SED; there is also no excess absorption beyond the (low) Galactic value detected in Chandra X-ray observations (Sako & Harrison 2002a). This is a high value for the SFR (see also Castro-Tirado et al 2007), although the S/N of the nIR spectrum implies a large uncertainty.…”

“…Despite the low amount of energy that was promptly released, this is among the most luminous afterglows ever detected (Kann et al 2006), even compared to a much larger Swift-era sample (Kann et al 2010). The multiwavelength temporal evolution of the GRB 021004 afterglow can be explained by multiple energy injections (Björnsson et al 2004;de Ugarte Postigo et al 2005), although other scenarios cannot be discarded (Lazzati et al 2002). GRB 021004 remains one of the most well-observed afterglows ever.…”

“…An extremely blue host galaxy was detected in late-time imaging de Ugarte Postigo et al 2005;Jakobsson et al 2005). To derive the star-formation rate (SFR), we studied the emission lines seen in the combined optical-nIR spectrum.…”

“…This prompted follow-up observations at many observatories, including extensive long-term coverage at X-rays (Sako & Harrison 2002a,b), radio Berger et al 2002;Pooley 2002a,b) 1 , millimeter (de Ugarte Postigo et al 2005), near-IR (de Ugarte Postigo et al 2005;Fynbo et al 2005), and optical wavelengths, both groundbased (Fox et al 2003;Bersier et al 2003;Uemura et al 2003;Holland et al 2003;Pandey et al 2003;Mirabal et al 2003;Kawabata et al 2004;de Ugarte Postigo et al 2005) and spacebased .…”