The X-ray afterglow of GRB 000926 observed by BeppoSAX and Chandra: A mildly collimated fireball in a dense medium?

L. Piro, G. Garmire, M. R. Garcia, L. A. Antonelli, E. Costa, M. Feroci, D. A. Frail, F. Harrison, K. Hurley, P. Mészáros, E. Waxman

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Abstract

We present X-ray observations of the afterglow of GRB 000926, performed around and after the break observed in the optical light curve 2 days after the burst. The steep X-ray light curve observed around the break confirms the presence of this feature in X-rays. However, the spectral and temporal properties are not consistent with a standard jet scenario based on synchrotron emission, requiring a more complicated model. We find that X-ray and optical data are compatible with a moderately collimated fireball (with opening angle θ ≈ 25°) expanding in a dense medium (n ≈ 4 × 104 cm-3). This produces two breaks in the light curve. The first, at t ≈ 2 days, is due to jet behavior. The second, around 5 days, is attributed to the transition of the fireball to a nonrelativistic expansion. This transition predicts a flattening of the light curve, which explains the late X-ray measurement in excess above the extrapolation of the simple jet scenario, and is also consistent with optical data.

Original languageEnglish (US)
Pages (from-to)442-447
Number of pages6
JournalAstrophysical Journal
Volume558
Issue number1 PART 1
DOIs
StatePublished - Sep 1 2001

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All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Piro, L., Garmire, G., Garcia, M. R., Antonelli, L. A., Costa, E., Feroci, M., Frail, D. A., Harrison, F., Hurley, K., Mészáros, P., & Waxman, E. (2001). The X-ray afterglow of GRB 000926 observed by BeppoSAX and Chandra: A mildly collimated fireball in a dense medium? Astrophysical Journal, 558(1 PART 1), 442-447. https://doi.org/10.1086/322467