Intermittent hydrodynamic jets in collapsars do not produce GRBs. (arXiv:2002.12384v3 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Gottlieb_O/0/1/0/all/0/1">Ore Gottlieb</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Levinson_A/0/1/0/all/0/1">Amir Levinson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nakar_E/0/1/0/all/0/1">Ehud Nakar</a>
Strong variability is a common characteristic of the prompt emission of
gamma-ray bursts (GRB). This observed variability is widely attributed to an
intermittency of the central engine, through formation of strong internal
shocks in the GRB-emitting jet expelled by the engine. In this paper we study
numerically the propagation of hydrodynamic jets, injected periodically by a
variable engine, through the envelope of a collapsed star. By post-processing
the output of 3D numerical simulations, we compute the net radiative efficiency
of the outflow. We find that all intermittent jets are subject to heavy baryon
contamination that inhibits the emission at and above the photosphere well
below detection limits. This is in contrast to continuous jets that, as shown
recently, produce a highly variable gamma-ray photospheric emission with high
efficiency, owing to the interaction of the jet with the stellar envelope. Our
results challenge the variable engine model for hydrodynamic jets, and may
impose constraints on the duty cycle of GRB engines. If such systems exist in
nature, they are not expected to produce bright gamma-ray emission, but should
appear as X-ray, optical and radio transients that resemble a delayed GRB
afterglow signal.
Strong variability is a common characteristic of the prompt emission of
gamma-ray bursts (GRB). This observed variability is widely attributed to an
intermittency of the central engine, through formation of strong internal
shocks in the GRB-emitting jet expelled by the engine. In this paper we study
numerically the propagation of hydrodynamic jets, injected periodically by a
variable engine, through the envelope of a collapsed star. By post-processing
the output of 3D numerical simulations, we compute the net radiative efficiency
of the outflow. We find that all intermittent jets are subject to heavy baryon
contamination that inhibits the emission at and above the photosphere well
below detection limits. This is in contrast to continuous jets that, as shown
recently, produce a highly variable gamma-ray photospheric emission with high
efficiency, owing to the interaction of the jet with the stellar envelope. Our
results challenge the variable engine model for hydrodynamic jets, and may
impose constraints on the duty cycle of GRB engines. If such systems exist in
nature, they are not expected to produce bright gamma-ray emission, but should
appear as X-ray, optical and radio transients that resemble a delayed GRB
afterglow signal.
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