REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination

By E. Molinari, S. Vergani, D. Malesani, S. Covino, P. D’Avanzo, G. Chincarini, F. Zerbi, L. A. Antonelli, P. Conconi, V. Testa and 25 more. 2006

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Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initia l fireball Lorentz factor 0. We aim to provide a direct measure of 0. Methods. The early-time afterglow light curve carries information about 0, which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afte rglows of GRB 060418 and GRB 060607A with the REM robotic telescope. Results. For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of 0∼ 400, fully confirming the highly relativistic nature of GRB fi reballs. The deceleration radius was inferred to be Rdec≈ 10 17 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e8c222394702779b79c929fd91ec693cc623ab32

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In Astronomy and Astrophysics

  1. E. Berger
  2. Bing Zhang
  3. B. Metzger
  4. D. Frail
  5. Joshua S. Bloom
  6. Shrinivas R. Kulkarni
  7. A. Filippenko
  8. D. Fox

In Instrumentation

  1. E. Berger
  2. A. Filippenko
  3. D. Frail
  4. S. Cenko
  5. J. Xavier Prochaska
  6. Joshua S. Bloom
  7. Shrinivas R. Kulkarni
  8. Karl Glazebrook

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