Rarefaction acceleration in magnetized gamma-ray burst jets

Sapountzis, K.; Vlahakis, N.

doi:10.1093/mnras/stt1142

Cited by 14 publications

(11 citation statements)

References 24 publications

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“…153 Numerical studies 132,154 predict an increasing opening angle during emergence and an inhomogeneous angular structure. 155 Emergent jet angular profiles can be translated into observational predictions using general analytic approximations to structured jets. [156][157][158][159][160][161] This would represent a departure from a 'top-hat' structure, where the energy is distributed evenly over the jet opening angle.…”

Section: Burrowing Through the Envelope Or Dense Environmentmentioning

confidence: 99%

Gamma-ray burst afterglow blast waves

Eerten

2018

Int. J. Mod. Phys. D

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The various stages of baryonic gamma-ray burst afterglow blast waves are reviewed. These are responsible for the afterglow emission from which much of our understanding of gamma-ray bursts derives. Initially, the blast waves are confined to the dense medium surrounding the burster (stellar envelope or dense wind), giving rise to a jet-cocoon structure. A massive ejecta is released and potentially fed by ongoing energy release from the burster and a forward-reverse shock system is set up between ejecta and ambient density. Ultimately the blast wave spreads sideways and slows down, and the dominant afterglow emission shifts from X-rays down to radio. Over the past years significant progress has been made both observationally and theoretically/numerically in our understanding of these blast waves, unique in the universe due to their often incredibly high initial Lorentz factors of 100-1000. The recent discovery of a short gamma-ray burst counterpart to a gravitational wave detection (GW 170817) brings the promise of a completely new avenue to explore and constrain the dynamics of gamma-ray burst blast waves. January 8, 2018 1:34 WSPC/INSTRUCTION FILE vanEerten˙IJMPD˙review-arXiv 2 Hendrik van EertenWhat ultimately tipped the scales firmly in favor of extra-galactic models involving cataclysmic events produced by individual or merging stars, were the 1997 discoveries of afterglows and the redshift distance determinations that these made possible. 4, 5 GRB afterglows had been predicted by a class of models (most explicitly, the fireball model 6, 7 ) positing a sudden deposition of a huge amount of energy at the site of a neutron star merger or massive star collapse. This was argued to trigger an expanding relativistic blast wave, which would ultimately decelerate and produce counterpart emission at a range of frequencies (i.e. X-rays and optical, 8 radio 9 ), as the energies of shock-accelerated particles in the blast wave shifted to lower peak values. The far smaller directional error circles from afterglow X-ray and optical measurements relative to gamma rays made the first host galaxy association 10, 11 possible (GRB 970228), at which point the verdict was unambiguously in.The first detected afterglow was connected to a long GRB. It had already become clear that there existed a bimodality in the distribution of GRB durations, with separate long and short duration populations on either side of a divide at roughly 2 seconds. 12 The aforementioned host galaxy association of GRB 970228 and in particular the measurement of a supernova (SN) counterpart to nearby (uniquely so, at z = 0.0085) GRB 980425, 13 firmly established a massive star origin for the long GRBs. The predominant model for short GRBs is that these are launched during the merger of two neutron stars. 14,15 Until very recently, the peer-reviewed evidence for the short GRB scenario remained indirect, and was based on e.g. time-scale arguments, host galaxy types and measured offsets relative to host galaxies (for a recent review, see e.g. 16 ). However, shor...

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Section: Burrowing Through the Envelope Or Dense Environmentmentioning

confidence: 99%

Gamma-ray burst afterglow blast waves

Eerten

2018

Int. J. Mod. Phys. D

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“…In such a case, the acceleration of the electron can be obtained through the reconnection process. Such a process can occur before or after the photospheric radius [96][97][98] and despite the extensive outgoing study of the process there are still even bigger ambiguities than the other two just mentioned [99]. For a review on the issue, the reader can refer Kagan et al [100].…”

Section: Radiative Processes In Jets: Emission Of Gamma Raysmentioning

confidence: 99%

Gamma Ray Bursts: Progenitors, Accretion in the Central Engine, Jet Acceleration Mechanisms

Janiuk¹,

Sapountzis²

2018

Cosmic Rays

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The collapsar model was proposed to explain the long-duration gamma ray bursts (GRBs), while the short GRBs are associated with the mergers of compact objects. In the first case, mainly the energetics of the events is consistent with the proposed progenitor models, while the duration, time variability, as well as the afterglow emission may shed some light on the detailed properties of the collapsing massive stars. In the latter case, the recent discovery of the binary neutron star (NS-NS) merger in the gravitational wave observation made by LIGO (GW170817) and the detection of associated electromagnetic counterparts, for the first time, gave a direct proof of the NS-NS merger being a progenitor of a short GRB. In general, all GRBs are believed to be powered by accretion through a rotationally supported torus, or by fast rotation of a compact object. For long ones, the rotation of the progenitor star is a key property in order to support accretion over relatively long activity periods and also to sustain the rotation of the black hole itself. The latter is responsible for ejection of the relativistic jets, which are powered due to the extraction of the BH rotational energy, mitigated by the accretion torus, and magnetic fields. The jets must break through the stellar envelope though, which poses a question on the efficiency of this process. Similar mechanisms of powering the jet ejection may act in short GRBs, which in this case may freely propagate through the interstellar medium. The power of the jets launched from the rotating black hole is at first associated mostly with the magnetic Poynting flux, and then, at large distances it is transferred to the kinetic and finally radiative energy of the expanding shells. Beyond the radiative processes expected to take place in the jet propagation phase after the stellar envelope crossing, the significant fraction of the jet acceleration is expected to take place inside the stellar envelope and just right after it in the case of a significant decrease of the exterior pressure support. The implications of the hot cocoon formed during the penetration of the stellar body and the interaction of the outflow with the surrounding material are crucial not only for the outflow collimation but also provide specific observational imprints with most notorious observed panchromatic break in the afterglow lightcurves. Thus a significant number of models have been developed for both matter and Poynting dominated otuflows. In this chapter, we discuss these processes from the theoretical point of view and we highlight the mechanisms responsible for the ultimate production of electromagnetic transients called GRBs. We also speculate on the possible GRB-GW associacion scenarios. Finally, in the context of the recently discovered short GRB and its extended multiwalength emission, we present a model that connects the neutron-rich ejecta launched from the accreting torus in the GRB engine with the production of the unstable heavy isotopes produced in the so-called r-process. The radioactive ...

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“…Related simulations by and Komissarov et al (2010) discuss this effect, and show that the efficiency of the magnetic acceleration (which was in effect inside the star leading to super-fast magnetosonic jet speed at breakout) is significantly increased. Subsequently Sapountzis and Vlahakis (2013) analyzed the effect using a steady-state, self-similar, relativistic MHD description of the rarefaction wave in planar geometry. This is to first order sufficient to study the effect which is important near the "corner" formed by the intersection of the jet and star surfaces.…”

Section: Rarefaction Accelerationmentioning

confidence: 99%

“…This is to first order sufficient to study the effect which is important near the "corner" formed by the intersection of the jet and star surfaces. The related equations can be found in Sapountzis and Vlahakis (2013). 5 The picture is much simplified if we neglect the poloidal magnetic field and the azimuthal bulk velocity (replaced by the O y component in the planar geometry), both of which are negligible in the super-fast magnetosonic regime.…”

Section: Rarefaction Accelerationmentioning

confidence: 99%

“…A few streamlines are shown (solid lines) together with the characteristics (dashed lines) and the Lorentz factor (color) space outside the jet is empty, then the tail of the rarefaction corresponds to D 0 and its polar angle is Â tail D 2 1=2 j = j .1 C j /. The momentum equation also gives the magnetization as a function of the polar angle Â D 15 and 7.16 show the resulting rarefied flow, a solution fromSapountzis and Vlahakis (2013).…”

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