GRB 070311: a direct link between the prompt emission and the afterglow

Abstract

Context. The prompt emission of gamma-ray bursts is mostly thought to be produced in internal shocks of relativistic shells emitted by the progenitor at different times, whereas the late multi-band afterglow is interpreted as the synchrotron emission of electrons swept up by the fireball expanding through the surrounding interstellar medium. The short timescale variability observed in flares superimposed on the X-ray/optical afterglow of several bursts, recently made possible by Swift, has been interpreted as evidence for prolonged activity of the inner engine through internal shocks. Yet, it is not clear whether this applies to all the observed bursts and, in particular, whether the bursts exhibiting single γ-ray pulses with no short timescale variability at late times could also be entirely interpreted as external shocks. Aims. We present prompt γ-ray, early NIR/optical, late optical and X-ray observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to gain clues on the mechanisms responsible for the prompt γ-ray pulse as well as for the early and late multiband afterglow of GRB 070311. Methods. We fitted with empirical functions the gamma-ray and optical light curves and scaled the result to the late time X-rays. Results. The H-band light curve taken by REM shows two pulses peaking 80 and 140 s after the peak of the γ-ray burst and possibly accompanied by a faint γ-ray tail. Remarkably, the late optical and X-ray afterglow underwent a major rebrightening between 3 × 10 4 and 2 × 10 5 s after the burst with an X-ray fluence comparable with that of the prompt emission extrapolated in the same band. Notably, the time profile of the late rebrightening can be described as the combination of a time-rescaled version of the prompt γ-ray pulse and an underlying power law. Conclusions. This result supports a common origin for both prompt and late X-ray/optical afterglow rebrightening of GRB 070311 within the external shock scenario. The main fireball would be responsible for the prompt emission, while a second shell would produce the rebrightening when impacting the leading blastwave in a refreshed shock.

The updated spectral catalogue of INTEGRAL gamma-ray bursts

“…Its spectrum is well described by a power law, with no improvement adopting other models. Our results are compatible with that of Sazonov et al (2007) and Guidorzi et al (2007b).…”

“…The afterglow was later observed by other observatories at optical wavelengths, and by the Swift/XRT at soft X-ray energies (Guidorzi et al 2007a). The light curve of the afterglow showed a major rebrightnening and other interesting features, described in detail in Guidorzi et al (2007b).…”

On the nature of the extremely fast optical rebrightening of the afterglow of GRB 081029

“…GRB 970508 showed a rebrightening of about 1.5 mag in I c , R and V bands around one day after the trigger (Sahu et al 1997;Vietri 1998;Sokolov et al 1998;Nardini et al 2006). Other cases reported in the literature are GRB 060206 (Monfardini et al 2006), GRB 070311 (Guidorzi et al 2007;Kong et al 2010), GGRB 71003 (Perley et al 2008;Ghisellini et al 2009), and GRB 071010A (Covino et al 2008b;Kong et al 2010).…”

First ALMA Light Curve Constrains Refreshed Reverse Shocks and Jet Magnetization in GRB 161219B

“…Ejecta released later, or at lower Lorentz factors than the initial impulsive shell responsible for the prompt emission, catch up with the contact discontinuity during the afterglow phase and inject energy into the FS (Rees & Meszaros 1998;Sari & Mészáros 2000). Energy injection through massive ejecta may explain late-time plateaus, rebrightening events, slow decays, and unexpected breaks observed in the X-ray and optical light curves of some afterglows (Kumar & Panaitescu 2000;Zhang & Mészáros 2002;Granot et al 2003;Panaitescu et al 2006;Guidorzi et al 2007;Mangano et al 2007;Margutti et al 2010a;Holland et al 2012;Li et al 2012;Greiner et al 2013;Panaitescu et al 2013;Nardini et al 2014;de Pasquale et al 2015;Beniamini & Mochkovitch 2017) and forms a distinct class of models from late-time central engine activity, which has been invoked to explain some rapid X-ray and optical flares (Burrows et al 2005b;Ioka et al 2005;Ghisellini et al 2009;Margutti et al 2010bMargutti et al , 2011Nardini et al 2010;Li et al 2012).…”