Skip to main content

Sub-photospheric shocks in relativistic explosions

Image: In the most common type of gamma-ray burst, illustrated here, a dying massive star forms a black hole (left), which drives a particle jet into space. Light across the spectrum arises from hot gas near the black hole, collisions within the jet, and from the jet's interaction with its surroundings. Credit: NASA's Goddard Space Flight Center


Astrophysical explosions and jets generate shock waves, which produce radiation. Their radiative properties are determined by the dissipation mechanism that sustains the velocity jump in the shock and by its ability to generate nonthermal particles.

A recent paper (Beloborodov 2016) examines the mechanism of internal shocks in gamma-ray bursts (GRBs) that occur before the GRB jets become transparent to radiation. The approach and some of the results may also be of interest for other explosions, e.g. in novae or supernovae.

Sub-photospheric shocks can produce neutrino emission and affect the observed photospheric radiation from the explosion. Shocks develop from internal compressive waves and can be of different types depending on the composition of the flow:
  1. Shocks in 'photon gas' with small plasma inertial mass have a unique structure determined by the 'force-free' condition -- zero radiation flux in the plasma rest frame. Radiation dominance over plasma inertia suppresses formation of collisionless shocks mediated by collective electromagnetic fields. 
  2. Strong collisionless subshocks develop in the opaque flow if it is sufficiently magnetized. The author evaluates the critical magnetization for this to happen. The collisionless subshock is embedded in a thicker radiation-mediated shock structure.
  3. Shocks in outflows carrying a free neutron component involve dissipation through nuclear collisions. At large optical depths, the shock thickness is comparable to the neutron free path, with an embedded radiation-mediated or collisionless subshock.
The author finds that sub-photospheric shocks are capable of generating high-energy particles and boosting the photon number carried by the outflow, and that the shock type changes as the outflow expands toward its photosphere. Strong e± pair creation occurs as the shock wave approaches the photosphere. Then the e±-dressed shock carries the photosphere with it up to two decades in radius, producing a strong observed pulse of nonthermal photospheric radiation.

  • Beloborodov 2016 (preprint) - Sub-photospheric shocks in relativistic explosions - (arXiv)
Etichette:

Comments

Post a Comment

Popular posts from this blog

THE HITCHCHIKER'S GUIDE TO THE LOCAL SUPERCLUSTER

Image: Virgo Supercluster. Credit: Andrew Z. Colvin The Virgo Supercluster is a region with a diameter of 33 megaparsecs (~1000 times larger the Milky Way's diameter) containing at least 100 galaxy groups and clusters.
Post a Comment
Read more

A METHOD TO TEST THE EXISTENCE OF REGULAR BLACK HOLES

Illustration of a black hole. Image Credit & Copyright: Alain Riazuelo The existence of the singularity is an intrinsic problem of the General Relativity (GR). At the fundamentally level, the resolution of the problem of the singularity lies with the expectation that under situations where quantum effects become strong, the behavior of gravity could possibly greatly deviate from that predicted by the classical theory of GR. Regular black hole solution are proposed with the same spacetime geometry outside the horizon as the traditional black hole, but bears no singularity inside. Whether or not black hole singularities should exist, they would be covered by the black hole horizon. The black hole horizon serves as an information curtain hindering outside observers from directly observing the interior structure of the black hole, and determining that whether or not the black hole singularity does really exist. A method is needed to check the correctness of the new constructions ...
Post a Comment
Read more

Boulevard of Broken Rings

Credit: ESO/Perrot This Picture illustrates the remarkable capabilities of SPHERE (the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument), a planet-hunting instrument mounted on ESO's Very Large Telescope (VLT) in Chile: It shows a series of broken rings of dust around a nearby star. These concentric rings are located in the inner region of the debris disc surrounding a young star named HD 141569A, which sits some 370 light-years away from us. In this image we see what is known as a transition disc, a short-lived stage between the protoplanetary phase, when planets have not yet formed, and a later time when planets have coalesced, leaving the disc populated only by any remaining - and predominantly dusty - debris. What we see here are structures formed of dust, revealed for the first time in near-infrared light by SPHERE - at a high enough resolution to capture remarkable detail! The area shown in this image has a diameter of just 200 times the Earth–Sun distan...
Post a Comment
Read more