Very Early Optical Afterglows of Gamma-Ray Bursts: Evidence for Relative Paucity of Detection

Peter W.~A. Roming, Patricia Schady, Derek B. Fox, Bing Zhang, Enwei Liang, Keith O. Mason, Evert Rol, David N. Burrows, Alex J. Blustin, Patricia T. Boyd, Peter Brown, Stephen T. Holland, Katherine McGowan, Wayne B. Landsman, Kim L. Page, James E. Rhoads, Simon R. Rosen, Daniel Vanden Berk, Scott D. Barthelmy, Alice A. BreeveldAntonino Cucchiara, Massimiliano De Pasquale, Edward E. Fenimore, Neil Gehrels, Caryl Gronwall, Dirk Grupe, Michael R. Goad, Mariya Ivanushkina, Cynthia James, Jamie A. Kennea, Shiho Kobayashi, Vanessa Mangano, Peter Mészáros, Adam N. Morgan, John A. Nousek, Julian P. Osborne, David M. Palmer, Tracey Poole, Martin D. Still, Gianpiero Tagliaferri, Silvia Zane

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77 Citations (SciVal)


Very early observations with the Swift satellite of γ-ray burst (GRB) afterglows reveal that the optical component is not detected in a large number of cases. This is in contrast to the bright optical flashes previously discovered in some GRBs (e.g., GRB 990123 and GRB 021211). Comparisons of the X-ray afterglow flux to the optical afterglow flux and prompt γ-ray fluence is used to quantify the seemingly deficient optical, and in some cases X-ray, light at these early epochs. This comparison reveals that some of these bursts appear to have higher than normal γ-ray efficiencies. We discuss possible mechanisms and their feasibility for explaining the apparent lack of early optical emission. The mechanisms considered include, foreground extinction, circumburst absorption, Lyα blanketing and absorption due to high-redshift, low-density environments, rapid temporal decay, and intrinsic weakness of the reverse shock. Of these, foreground extinction, circumburst absorption, and high redshift provide the best explanations for most of the nondetections in our sample. There is tentative evidence of suppression of the strong reverse shock emission. This could be because of a Poynting flux-dominated flow or a pure nonrelativistic hydrodynamic reverse shock.
Original languageEnglish
Pages (from-to)1416-1422
Number of pages7
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 1 Dec 2006


  • Gamma Rays: Bursts, Astrophysics


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