English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

We present X-ray observations of the afterglow of GRB000926 performed aroundand after the break observed in the optical light curve two days after theburst. The steep X-ray light curve observed around the break confirms thepresence of this feature in X-rays. However, the spectral and temporalproperties are not consistent with a standard jet scenario based on synchrotronemission, requiring a more complicated model. We find that X-ray and opticaldata are compatible with a moderately collimated fireball (with opening angle$\theta\approx25 \deg$) expanding in a dense medium ($n\approx 4\times 10^4$cm$^{-3}$). This produces two breaks in the light curve. The first, at$t\approx$ 2 days, is due to jet behavior. The second, around 5 days, isattributed to the transition of the fireball to a non-relativistic expansion.This transition predicts a{\it flattening} of the light curve, that explainsthe late X-ray measurement in excess above the extrapolation of the simple jetscenario, and is also consistent with optical data.Comment: 19 pages, 3 fig.s, minor revisions, accepted for publication in Ap

The X‐Ray Afterglow of GRB 000926 Observed byBeppoSAXandChandra: A Mildly Collimated Fireball in a Dense Medium?