523 research outputs found
Dynamical Evolution of an Ultra-relativistic Fireball Colliding with a Freely Expanding Gas
We investigate the hydrodynamical evolution of an ultra-relativistic fireball
colliding with a freely expanding gas. The hydrodynamical interaction of the
fireball and the gas results in the formation of a geometrically thin shell. We
study the dynamical evolution of the shell by an analytical way and perform a
numerical simulation equipped with an adaptive mesh refinement to investigate
the internal structure of the shell. The shocked gas can give rise to bright
emission in the X-ray and gamma-ray energy range. We propose that the breakout
emission from the forward shock and the photospheric emission from the
reverse-shocked fireball contribute to early gamma-ray emission from gamma-ray
bursts.Comment: 15 pages, 9 figures, accepted for publication in Ap
Early evolution of spherical ejecta expanding into the circumstellar matter at ultra-relativistic speeds
We present a new self-similar solution describing early evolution of an
ultra-relativistic flow resulting from a collision of homologously expanding
spherical ejecta with the circumstellar matter, in which a shock wave
propagates in the circumstellar matter while a weak discontinuity propagates in
the ejecta at the sound speedComment: 5 pages, 2 figures, accepted for publication in PAS
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