scholarly journals The Nature of Flat Spectrum Sources

1996 ◽  
Vol 175 ◽  
pp. 423-426
Author(s):  
D.B. Melrose
Keyword(s):  
Galactic Center ◽  
Basic Mechanism ◽  
Electron Energy Spectrum ◽  
Shock Acceleration ◽  
Radio Sources ◽  
Fermi Acceleration ◽  
Diffusive Shock Acceleration ◽  
Nonthermal Radio ◽  
Pile Up ◽  
Multiple Shocks

Nonthermal radio sources near the Galactic Center with flat or weakly inverted spectra (S((ω) ∝ ωα with α ≳ 0) are attributed to optically thin synchrotron emission from a hard electron energy spectrum, N(ε) ∝ ε–α with a = 1 – 2α ≲ 1, produced by Fermi acceleration or diffusive shock acceleration at multiple shocks combined with a synchrotron pile up. This basic mechanism is also plausible for flat-spectrum AGN.

Shock Acceleration in Hot Spots

1996 ◽  
Vol 13 (2) ◽  
pp. 132-139 ◽  
Author(s):  
M. H. Pope ◽  
Lewis Ball ◽  
D. B. Melrose
Keyword(s):  
Simple Model ◽  
Hot Spots ◽  
Electron Acceleration ◽  
Shock Acceleration ◽  
Model Parameters ◽  
Radio Sources ◽  
Diffusive Shock Acceleration ◽  
Extragalactic Radio Sources ◽  
Multiple Shocks

AbstractA simple model is presented for electron acceleration in extragalactic radio sources with two hot spots. The effect of diffusive shock acceleration by multiple shocks is calculated numerically, with adiabatic and synchrotron losses included. It is found for the sources 3C 20 and 3C 268·4 that a consistent set of model parameters exists which reproduce the observations. The model fails to reproduce the observations for the source 3C 196.

scholarly journals The Compact Nonthermal Radio Source at the Galactic Center: an Update

1989 ◽  
Vol 136 ◽  
pp. 527-534
Author(s):  
K. Y. Lo
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Central Star ◽  
Radio Sources ◽  
Stellar Objects ◽  
Nonthermal Radio ◽  
Compact Radio Source ◽  
The Galaxy ◽  
Observational Status ◽  
Sgr A

We review the current observational status of Sgr A∗, the compact nonthermal radio source at the galactic center. Sgr A∗ is a unique radio source at a unique location of the Galaxy. It is unlike any compact radio source associated with known stellar objects, but it is similar to extragalactic nuclear compact radio sources. The positional offset between Sgr A∗ and IRS16 places little constraint on the nature of the underlying energy source, since IRS16 need not be the core of the central star cluster. Sgr A∗ is still the best candidate for marking the location of a massive collapsed object.

Diffusive Shock Acceleration by Multiple Shock Fronts with Differing Properties

1994 ◽  
Vol 11 (2) ◽  
pp. 175-179 ◽  
Author(s):  
M. H. Pope ◽  
D. B. Melrose
Keyword(s):  
Spectral Index ◽  
Asymptotic Limit ◽  
Shock Acceleration ◽  
Shock Strength ◽  
Adiabatic Expansion ◽  
Diffusive Shock Acceleration ◽  
The Mean ◽  
Multiple Shocks ◽  
Shock Fronts ◽  
Multiple Shock

AbstractThe effect of diffusive shock acceleration on a distribution of particles is explored for multiple shocks, taking into account adiabatic expansion between the shocks. Specifically, the spectral index is calculated numerically for two cases: a sequence of identical shocks, and a sequence of pairs of shocks with alternating shock strength. How these two cases evolve to the asymptotic limit is examined, and it is shown that the evolution of the paired-shock case can be described by a sequence of identical shocks with shock strength equal to the mean of the two.

Diffusive Shock Acceleration by Multiple Shocks

1993 ◽  
Vol 10 (3) ◽  
pp. 222-224 ◽  
Author(s):  
D.B. Melrose ◽  
M.H. Pope
Keyword(s):  
Finite Number ◽  
Power Law ◽  
Momentum Distribution ◽  
Strong Shock ◽  
High Energy ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Single Shock ◽  
Multiple Shocks

AbstractDiffusive shock acceleration produces a power law momentum distribution f(p)α p−b, with b ≥ 4 for a single shock, and b = 4 for a single strong shock. It has been shown that the distribution for acceleration at a sequence of identical shocks is flatter, approaching f(p)α p−3 below a high energy knee, for an arbitrarily large number of shocks. We show how this flatter distribution arises and discuss the range of momenta over which it extends after a finite number of shocks.

scholarly journals Interaction of Jets with Clouds in Extragalactic Radio Sources

1994 ◽  
Vol 159 ◽  
pp. 346-346
Author(s):  
V. Fedorenko ◽  
A. Zentsova ◽  
T. J.-L. Courvoisier ◽  
S. Paltani
Keyword(s):  
Magnetic Field ◽  
Supernova Remnants ◽  
Shock Acceleration ◽  
Stellar Winds ◽  
Radio Sources ◽  
Red Giants ◽  
Diffusive Shock Acceleration ◽  
Extragalactic Jets ◽  
The Magnetic Field ◽  
Very High

Several points indicate that extragalactic jets can interact with dense gaseous obstacles which occur on their ways. Examples of these interactions are the knotty structure of the radio and optical jet in M 87 and in other objects. These observations have been interpreted by Blandford & Königl in terms of collision of a jet with supernova remnants. We have reanalysed this idea taking into account new observations and improvements in the theory of diffusive shock acceleration. We find that the model requires a very high supernova birthrate (∼ 1 SN/year), which is not observed. It is more probable that the “obstacles” are formed by the stellar winds from the red giants. We estimate that the value of the magnetic field is ∼ 10−5 G in the interaction region (r=1kpc) (paper in preparation).

scholarly journals Electron Acceleration in Solar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 95-103
Author(s):  
Wolfgang Dröge ◽  
Peter Meyer ◽  
Paul Evenson ◽  
Dan Moses
Keyword(s):  
Power Law ◽  
Distribution Functions ◽  
Shock Acceleration ◽  
Fermi Acceleration ◽  
Diffusive Shock Acceleration ◽  
X Ray ◽  
Electron Spectra ◽  
Flare Loops ◽  
Long Duration ◽  
The One

AbstractFor the period September 1978 to December 1982 we have identified 55 solar flare particle events for which our instruments on board the ISEE-3 (ICE) spacecraft detected electrons above 10 MeV. Combining our data with those from the ULEWAT spectrometer (MPI Garching and University of Maryland) electron spectra in the range from 0.1 to 100 MeV were obtained. The observed spectral shapes can be divided into two classes. The spectra of the one class can be fit by a single power law in rigidity over the entire observed range. The spectra of the other class deviate from a power law, instead exhibiting a steepening at low rigidities and a flattening at high rigidities. Events with power-law spectra are associated with impulsive (< 1 hr duration) soft X-ray emission, whereas events with hardening spectra are associated with long-duration (> 1 hr) soft X-ray emission. The characteristics of long-duration events are consistent with diffusive shock acceleration taking place high in the corona. Electron spectra of short-duration flares are well reproduced by the distribution functions derived from a model assuming simultaneous second-order Fermi acceleration and Coulomb losses operating in closed flare loops.

scholarly journals Effects of the solar wind termination shock and heliosheath on theheliospheric modulation of galactic and anomalous Helium

2004 ◽  
Vol 22 (8) ◽  
pp. 3063-3072 ◽  
Author(s):  
U. W. Langner ◽  
M. S. Potgieter
Keyword(s):  
Solar Wind ◽  
Cosmic Ray ◽  
Magnetic Polarity ◽  
Termination Shock ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Cosmic Ray Modulation ◽  
Low Energies ◽  
Solar Wind Termination Shock ◽  
Charge Sign

Abstract. The interest in the role of the solar wind termination shock and heliosheath in cosmic ray modulation studies has increased significantly as the Voyager 1 and 2 spacecraft approach the estimated position of the solar wind termination shock. The effect of the solar wind termination shock on charge-sign dependent modulation, as is experienced by galactic cosmic ray Helium (He++) and anomalous Helium (He+), is the main topic of this work, and is complementary to the previous work on protons, anti-protons, electrons, and positrons. The modulation of galactic and anomalous Helium is studied with a numerical model including a more fundamental and comprehensive set of diffusion coefficients, a solar wind termination shock with diffusive shock acceleration, a heliosheath and particle drifts. The model allows a comparison of modulation with and without a solar wind termination shock and is applicable to a number of cosmic ray species during both magnetic polarity cycles of the Sun. The modulation of Helium, including an anomalous component, is also done to establish charge-sign dependence at low energies. We found that the heliosheath is important for cosmic ray modulation and that its effect on modulation is very similar for protons and Helium. The local Helium interstellar spectrum may not be known at energies

scholarly journals Turbulent Origin of the Galactic Center Magnetic Field: Nonthermal Radio Filaments

2006 ◽  
Vol 637 (2) ◽  
pp. L101-L104 ◽  
Author(s):  
Stanislav Boldyrev ◽  
Farhad Yusef-Zadeh
Keyword(s):  
Magnetic Field ◽  
Galactic Center ◽  
Nonthermal Radio

scholarly journals DIFFUSIVE SHOCK ACCELERATION SIMULATIONS OF RADIO RELICS

2012 ◽  
Vol 756 (1) ◽  
pp. 97 ◽  
Author(s):  
Hyesung Kang ◽  
Dongsu Ryu ◽  
T. W. Jones
Keyword(s):  
Shock Acceleration ◽  
Diffusive Shock Acceleration
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