The afterglow of GRB 021004: surfing on density waves

By D. Lazzati, E. Rossi, S. Covino, G. Ghisellini, D. Malesani. 2002

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We present a model for the early optical afterglow of GRB 021004. This burst had one of the earliest detected optical afterglows, allowing for a dense optical sampling. The lightcurve was peculiar, since bright bumps were superimposed to the regular power-law decay observed in many other events. We show that, given their time scale and shape, the bumps are likely due to the interaction of the fireball with moderate density enhancements in the ambient medium. The enhancements have a density contrast of order 10, modifying only slightly the dynamics of the fireball, which therefore surfs on them rather than colliding into them. A relativistic reverse shock does not develop. Since the interaction takes place when the fireball is still hyper-relativistic it is not possible to understand if the overdensities are localized in clumps or are spherically symmetric around the GRB progenitor. The monotonic decrease of the contrast of successive rebrightenings suggests however the presence of clumps embedded in a uniform environment. Such an interpretation, complemented by the detection of several high velocity absorption systems in the optical spectrum, strongly suggests that GRB 021004 exploded within the remnant of a previous explosion.

Subfields: Astronomy and Astrophysics, Instrumentation, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/29621a90173154736aa3fc01faf7e6b5ecef4c1b

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Citations in the corpus

Gamma-ray burst afterglows (2006, background): “…to interpret these variabilities usually invoke external shock related processes, such as density fluctuation , inhomogeneous jets, refreshed shocks, or multiple component jets (Lazzati et al. 2002; Heyl & Perna 2003; Nakar et al. 2003; Berger et al. 2003a; Granot et al. 2003; Ioka et al. 2005).”
AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “Possible explanations include a sharp change in the circumburst density (e.g., Lazzati et al. 2002; Tam et al. 2005 but, c.f. Nakar & Granot 2007) or a smooth injection of energy into the forward shock from the central engine (e.g., Rees & Meszaros 1998).”
Variabilities of Gamma-Ray Burst Afterglows: Long-acting Engine, Anisotropic Jet, or Many Fluctuating Regions? (2004, background): “Ambient density fluctuations may lead to afterglow variabilities (Wang & Loeb 2000; Lazzati et al. 2002; Dai & Lu 2002; Nakar, Piran, & Granot 2003).”
The physics of gamma-ray bursts & relativistic jets (2014, background): “These may lead to bump features in afterglow lightcurves (Dai and Lu, 2002; Lazzati et al., 2002; Dai and Wu, 2003; Pe’er and Wijers, 2006).”
Evidence for a Canonical Gamma-Ray Burst Afterglow Light Curve in the Swift XRT Data (2005, background): “…external shock, be it from refreshed shocks20 (Kumar & Piran 2000a; Granot et al. 2003; Ramirez-Ruiz et al. 2001b), bumps in the external medium (Lazzati et al. 2002; Nakar et al. 2003; Ramirez-Ruiz et al. 2001a), or angular inhomogeneities in the outflow (Fenimore et al. 1999a; Nakar et al.…”
Gamma-Ray Bursts in the Swift Era (2007, background): “…external shock related processes, such as refreshedshocks, density fluctuation, inhomogeneous jets, or multiple component jets (Panaitescu et al. 1998; Zhang & Mészáros 2002a; Lazzati et al. 2002; Heyl & Perna 2003; Nakar et al. 2003; Berger et al. 2003a; Granot et al. 2003; Ioka et al. 2005).”
Gamma-Ray Burst Energetics and the Gamma-Ray Burst Hubble Diagram: Promises and Limitations (2003, background): “Since the environments of a least some GRBs are thought to be clumpy (Lazzati et al. 2002; Bersier et al. 2003; Heyl & Perna 2003) and wind-blown [i.e., ðrÞ / r 2; Chevalier & Li 1999; Price et al. 2002b], this is clearly not the case for all GRBs in our sample; therefore, our estimations of fb may…”
Physical Processes Shaping Gamma-Ray Burst X-Ray Afterglow Light Curves: Theoretical Implications from the Swift X-Ray Telescope Observations (2005, background): “The light curves for a blast wave surfing on a density wave should be generally quite smooth (cf. Lazzati et al. 2002).”
The 2175 Å Dust Feature in a Gamma-Ray Burst Afterglow at Redshift 2.45 (2008, background): “Possible explanations include inhomogeneities in the density profile of the circumburst medium (e.g., Wang & Loeb 2000; Lazzati et al. 2002) or in the angular distribution of the outflow (i.e., the patchy shell model; Kumar & Piran 2000), or late energy injection by refreshed shocks (e.g., Rees &…”
The Supernova Gamma-Ray Burst Connection (2006, background): “Other (less locally based) origins are possible, such as SNe remnants (Lazzati et al., 2002), quasar absorption systems (Mirabal et al., 2002), or galactic superwinds.”