Testing the External Shock Model of Gamma-Ray Bursts using the Late-Time Simultaneous Optical and X-ray Afterglows

We study the ``normal'' decay phase of the X-ray afterglows of gamma-ray bursts (GRBs), which follows the shallow decay phase, using the events simultaneously observed in the R-band. The classical external shock model -- in which neither the delayed energy injection nor time-dependency of shock micro-physics is considered -- shows that the decay indices of the X-ray and R-band light curves, $\alpha_{\rm X}$ and $\alpha_{\rm O}$, obey a certain relation, and that in particular, $\alpha_{\rm O}-\alpha_{\rm X}$ should be larger than -1/4 unless the ambient density increases with the distance from the central engine. For our selected 14 samples, we have found that 4 events violate the limit at more than the 3$\sigma$ level, so that a fraction of events are outliers of the classical external shock model at the ``normal'' decay phase.Comment: Accepted for publication in ApJL. 12 page, 2 figures, 2 table

Relationship between Concentration of Chemical Substances in Estuarine Sediments and Concentration of Vitellogenin in Mudskipper (Periophthalmus modestus) and Common Goby (Acanthogobius flavimanus) Serum

Sediments, mudskippers, and common gobies were collected from the estuaries of nine rivers along the coast of the Ariake Sea in the northwestern part of Kyushu. The sediments were analyzed for alkylphenols, organotin compounds, and polycyclic aromatic hydrocarbons. Then, male mudskippers and common gobies were analyzed for serum vitellogenin concentration. Sediments from the estuary of the Omuta River, which has residential areas in its upper reaches and many large-scale chemical plants in its lower reaches, exhibited higher concentrations of these three types of chemicals than the other rivers, and male mudskippers caught in the Omuta River exhibited higher serum vitellogenin concentrations than mudskippers caught in other rivers. One chemical substance thought to be responsible for these elevated vitellogenin concentrations is nonylphenol, a type of alkylphenol. Male common gobies caught in the Suwa River exhibited higher vitellogenin concentrations than common gobies caught in other rivers. Although the Suwa River had high polycyclic aromatic hydrocarbon concentrations, the elevated vitellogenin concentrations of these male common gobies were thought to be attributable to factors such as sewage treatment plants, not polycyclic aromatic hydrocarbons. However, organotin compounds were detected in all estuarine sediments. This was attributed to the fact that the Ariake Sea is a good area for fishing and a number of small fishing vessels anchor and operate in the estuaries of all these rivers.Nagasaki University Major Research Project: Restoration of Marine Environment and Resources in East Asi