Testing the external-shock model of gamma-ray bursts using the late-time simultaneous optical and X-ray afterglows

Yuji Urata, Ryo Yamazaki, Takanori Sakamoto, Kuiyun Huang, Weikang Zheng, Goro Sato, Tsutomu Aoki, Jinsong Deng, Kunihito Ioka, WingHuen Ip, Koji S. Kawabata, Yihsi Lee, Xin Liping, Hiroyuki Mito, Takashi Miyata, Yoshikazu Nakada, Takashi Ohsugi, Yulei Qiu, Takao Soyano, Kenichi TarusawaMakoto Tashiro, Makoto Uemura, Jianyan Wei, Takuya Yamashita

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21 Citations (Scopus)

Abstract

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 microphysics is consideredshows that the decay indices of the X-ray and R-band light curves, αx and αo, obey a certain relation, and that in particular, αo - αx 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 four events violate the limit at more than the 3 σ level, so that a fraction of events are outliers of the classical external-shock model at the "normal" decay phase.

Original languageEnglish
JournalAstrophysical Journal
Volume668
Issue number2 PART 2
DOIs
Publication statusPublished - 2007

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Keywords

  • Gamma rays: bursts
  • Gamma rays: observations

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Urata, Y., Yamazaki, R., Sakamoto, T., Huang, K., Zheng, W., Sato, G., Aoki, T., Deng, J., Ioka, K., Ip, W., Kawabata, K. S., Lee, Y., Liping, X., Mito, H., Miyata, T., Nakada, Y., Ohsugi, T., Qiu, Y., Soyano, T., ... Yamashita, T. (2007). Testing the external-shock model of gamma-ray bursts using the late-time simultaneous optical and X-ray afterglows. Astrophysical Journal, 668(2 PART 2). https://doi.org/10.1086/522930