Intergalactic shock acceleration and the cosmic gamma-ray background     

Francesco Miniati 《Monthly notices of the Royal Astronomical Society》2002,337(1):199-208

We investigate numerically the contribution to the cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation. We show that the kinetic energy of accretion flows in the low-redshift intergalactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmic-ray pressure. Cosmic rays accelerated at these shocks produce a diffuse gamma-ray flux which is dominated by inverse Compton emission from electrons scattering off cosmic microwave background photons. Decay of neutral π mesons generated in p–p inelastic collisions of the ionic cosmic-ray component with the thermal gas contribute about 30 per cent of the computed emission. Based on experimental upper limits on the photon flux above 100 MeV from nearby clusters we constrain the efficiency of conversion of shock ram pressure into relativistic CR electrons to  ≲1 per cent  . Thus, we find that cosmic rays of cosmological origin can generate an overall significant fraction of order 20 per cent and no more than 30 per cent of the measured gamma-ray background.  相似文献   

A stability analysis of radiative shocks in the presence of a transverse magnetic field     

Babulakshmanan Ramachandran  Michael D. Smith 《Monthly notices of the Royal Astronomical Society》2005,362(4):1353-1362

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The effect of curvature on detonation waves in Type Ia supernovae     

Gary J. Sharpe 《Monthly notices of the Royal Astronomical Society》2001,322(3):614-624

The effect of curvature on detonation speed and structure for detonation waves in C–O is investigated. Weakly curved detonation fronts have a sonic point inside the reaction zone. In such waves the detonation speed depends on the detailed internal structure and not on simple jump conditions. Hence, in order to obtain the correct propagation speed and products of burning, the reaction length-scales must be resolved in any numerical simulation involving curved detonations in C–O. For each value of the initial density there is a corresponding extinction curvature above which quasi-steady detonations cannot propagate. For densities less than 2×10⁷ g cm⁻³, where the self-sustaining planar waves are Chapman–Jouguet, and for realistic values of the curvature, the sonic point moves from the end of silicon burning to the end of oxygen burning. Hence the effective detonation length, i.e. the length-scale of the burning between the shock and the sonic point which can affect the front, is several orders of magnitudes less than the planar waves predict. However, silicon burning, which occurs downstream of the sonic point, is increased in length by a few orders of magnitude owing to lower detonation speeds and temperatures. Therefore more intermediate-mass elements will be produced by incomplete burning if curvature is taken into account. Recent advances in detonation theory and modelling are also discussed in the context of Type Ia supernovae.  相似文献   

Mach number dependence of the onset of dynamo action     

Nils Erland L. Haugen  Axel Brandenburg  Antony J. Mee 《Monthly notices of the Royal Astronomical Society》2004,353(3):947-952

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Swift gamma-ray burst afterglows and the forward-shock model     

A. Panaitescu 《Monthly notices of the Royal Astronomical Society》2007,379(1):331-342

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The Formation of a Cooling Layer in a Partially Optically Thick Shock     

A. B. Reighard  R. P. Drake 《Astrophysics and Space Science》2007,307(1-3):121-125

The mechanics of a radiative shock which has “collapsed,” or been compressed to high density, via radiative cooling is discussed. This process is relevant to an experiment in xenon gas that produced a driven, radiatively collapsed shock, and also to a simulation of the supernova 1987A shock wave passing through the outer layers of the star and into the low-density circumstellar material.  相似文献   

Code Development of Three-Dimensional General Relativistic Hydrodynamics with AMR (Adaptive-Mesh Refinement) and Results from Special and General Relativistic Hydrodynamics     

Orhan Dönmez 《Astrophysics and Space Science》2004,293(3):323-354

In this paper, the general procedure to solve the general relativistic hydrodynamical (GRH) equations with adaptive-mesh refinement (AMR) is presented. In order to achieve, the GRH equations are written in the conservation form to exploit their hyperbolic character. The numerical solutions of GRH equations are obtained by high resolution shock Capturing schemes (HRSC), specifically designed to solve nonlinear hyperbolic systems of conservation laws. These schemes depend on the characteristic information of the system. The Marquina fluxes with MUSCL left and right states are used to solve GRH equations. First, different test problems with uniform and AMR grids on the special relativistic hydrodynamics equations are carried out to verify the second-order convergence of the code in one, two and three dimensions. Results from uniform and AMR grid are compared. It is found that adaptive grid does a better job when the number of resolution is increased. Second, the GRH equations are tested using two different test problems which are Geodesic flow and Circular motion of particle In order to do this, the flux part of GRH equations is coupled with source part using Strang splitting. The coupling of the GRH equations is carried out in a treatment which gives second order accurate solutions in space and time. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The radio flaring behaviour of GRO J1655−40: an analogy with extragalactic radio sources?     

J. A. Stevens &#;  D. C. Hannikainen  Kinwah Wu  R. W. Hunstead  D. J. McKay 《Monthly notices of the Royal Astronomical Society》2003,342(2):623-628

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A numerical scheme for multifluid magnetohydrodynamics     

S. A. E. G. Falle 《Monthly notices of the Royal Astronomical Society》2003,344(4):1210-1218

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A unified treatment of the gamma-ray burst 021211 and its afterglow     

Pawan Kumar  Alin Panaitescu 《Monthly notices of the Royal Astronomical Society》2003,346(3):905-914

The gamma-ray burst (GRB) 021211 had a simple light curve, containing only one peak and the expected Poisson fluctuations. Such a burst may be attributed to an external shock, offering the best chance for a unified understanding of the gamma-ray burst and afterglow emissions. We analyse the properties of the prompt (burst) and delayed (afterglow) emissions of GRB 021211 within the fireball model. Consistency between the optical emission during the first 11 min (which, presumably, comes from the reverse shock heating of the ejecta) and the later afterglow emission (arising from the forward shock) requires that, at the onset of deceleration (∼2 s), the energy density in the magnetic field in the ejecta, expressed as a fraction of the equipartition value  (ɛ _B )  , is larger than in the forward shock at 11 min by a factor of approximately 10³. We find that synchrotron radiation from the forward shock can account for the gamma-ray emission of GRB 021211; to explain the observed GRB peak flux requires that, at 2 s,  ɛ _B   in the forward shock is larger by a factor 100 than at 11 min. These results suggest that the magnetic field in the reverse shock and early forward shock is a frozen-in field originating in the explosion and that most of the energy in the explosion was initially stored in the magnetic field. We can rule out the possibility that the ejecta from the burst for GRB 021211 contained more than 10 electron–positron pairs per proton.  相似文献