scholarly journals Particle Acceleration and Radio Emission of the Supernovae Remnants at Different Stages of their Evolution

1983 ◽  
Vol 101 ◽  
pp. 183-186
Author(s):  
V. N. Fedorenko
Keyword(s):  
Magnetic Field ◽  
Shock Wave ◽  
Particle Acceleration ◽  
Radio Emission ◽  
Temporal Evolution ◽  
Relativistic Electrons ◽  
List Type ◽  
Type Number ◽  
Physical Processes ◽  
The Magnetic Field

In this Paper, I consider physical processes, governing relativistic electrons in SNRs. a)SNRs at the age t > 102 yr. I argue that the shock wave acceleration faces some difficulties. Then I show that the temporal evolution of the SNRs radio emission can be accounted for without involving the acceleration.b)SNRs at the age t < 102 yr. I associate the lack of radio emission at this stage (Brown and Marscher, 1978) with the weakness of the magnetic field.c)I infer that the most efficient particle acceleration and radio emission of the SNRs should occur at the stage t ~ 102 yr.

scholarly journals Implications of the Low-frequency Turnover in the Spectrum of Radio Knot C in DG Tau

2021 ◽  
Vol 923 (1) ◽  
pp. 61
Author(s):  
C.-I. Björnsson
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Radio Emission ◽  
Magnetic Field Strength ◽  
Spectral Index ◽  
Low Frequency ◽  
Relativistic Electrons ◽  
Fermi Acceleration ◽  
Emission Volume ◽  
The Magnetic Field

Abstract The synchrotron spectrum of radio knot C in the protostellar object DG Tau has a low-frequency turnover. This is used to show that its magnetic field strength is likely to be at least 10 mG, which is roughly two orders of magnitude larger than previously estimated. The earlier, lower value is due to an overestimate of the emission volume together with an omission of the dependence of the minimum magnetic field on the synchrotron spectral index. Since the source is partially resolved, this implies a low volume-filling factor for the synchrotron emission. It is argued that the high pressure needed to account for the observations is due to shocks. In addition, cooling of the thermal gas is probably necessary in order to further enhance the magnetic field strength as well as the density of relativistic electrons. It is suggested that the observed spectral index implies that the energy of the radio-emitting electrons is below that needed to take part in first-order Fermi acceleration. Hence, the radio emission gives insights to the properties of its pre-acceleration phase. Attention is also drawn to the similarities between the properties of radio knot C and the shock-induced radio emission in supernovae.

scholarly journals Particle Acceleration in the Process of Eruptive Opening and Reconnection of Magnetic Fields

1980 ◽  
Vol 91 ◽  
pp. 217-221 ◽  
Author(s):  
Z. Švestka ◽  
S. F. Martin ◽  
R. A. Kopp
Keyword(s):  
Magnetic Field ◽  
Shock Wave ◽  
Particle Acceleration ◽  
Magnetic Fields ◽  
Magnetic Loop ◽  
Coronal Loops ◽  
X Rays ◽  
Flare Loops ◽  
Field Lines ◽  
The Magnetic Field

In a series of papers on the flare of 29 July 1973 (Nolte et al., 1979; Martin, 1979; Švestka et al., 1979) it has been shown that Hα “post-flare” loops are the cooled aftermath of previously hot coronal loops which were visible in x-rays in the same position earlier in the flare. Kopp and Pneuman (1976) have proposed that these post-flare loops are formed by a process of successive magnetic field reconnections of previously distended magnetic field lines as illustrated in Figure 1. Each successive reconnection of the magnetic field yields a closed magnetic loop that forms above and concentric with previously formed loops. A shock wave created during each sudden reconnection travels down both legs of each loop and provides energy for ionizing chromospheric mass at the footpoints of the loop. Subsequent condensation of the ionized mass at the tops of the loops renders them visible as this mass falls to the chromosphere.

scholarly journals A Most Energetic Type Ic Supernova: SN 2003L

2005 ◽  
Vol 192 ◽  
pp. 117-121
Author(s):  
Alicia M. Soderberg
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Density Profile ◽  
Temporal Evolution ◽  
Surrounding Medium ◽  
Physical Parameters ◽  
Radio Luminosity ◽  
Radio Data ◽  
Show Evidence ◽  
The Magnetic Field

SummaryWe present extensive radio observations of SN2003L, the most luminous and energetic Type Ic radio supernova with the exception of SN 1998bw. Using radio data, we are able to constrain the physical parameters of the supernova, including the velocity and energy of the fastest ejecta, the temporal evolution of the magnetic field, and the density profile of the surrounding medium. We highlight the extraordinary properties of the radio emission with respect to the supernova’s normal characteristics within optical bands. We find that although the explosion does not show evidence for a significant amount of relativistic ejecta, it produces a radio luminosity which is comparable to that seen in the unusual SN1998bw. Using SN2003L as an example, we comment briefly on the broad diversity of type Ic properties and the associated implications for progenitor models.

scholarly journals On the magnetic structure of an active region

1968 ◽  
Vol 35 ◽  
pp. 126-126
Author(s):  
F. A. Ermakov ◽  
E. I. Mogilevsky ◽  
B. D. Shelting
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
General Structure ◽  
Convective Zone ◽  
List Type ◽  
Type Number ◽  
Magnetic Field Generation ◽  
Field Amplification ◽  
The Magnetic Field ◽  
A Current

(1)A scheme of magnetic-field generation in an active region within the subphotospheric convective zone is discussed. Magnetic-field amplification is considered to result from the interaction of the local cyclonic motion and the turbulent motion of the subphotospheric plasma.(2)A model of the magnetoplasma of an active region is considered consisting of a current-free magnetic field, whose lines of force stretch deeply under the photosphere in the form of subgranules (force-free fine-scale plasma elements). The explanation of some peculiarities in the development of an active region with the considered structure is discussed.(3)Some peculiarities of the general structure of the magnetic field and the motion within photosphere and chromosphere obtained by the analysis of observations with the IZMIRAN two-channel magnetograph is discussed.

scholarly journals 3C205 - A Source with Extraordinary Alignment and a VLBI Hotspot

1984 ◽  
Vol 110 ◽  
pp. 41-42
Author(s):  
C. J. Lonsdale
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Energy Density ◽  
Internal Energy ◽  
High Redshift ◽  
Position Angle ◽  
List Type ◽  
Type Number ◽  
The Core ◽  
The Magnetic Field

High resolution maps of 3C205 using MERLIN and the European VLBI network (EVN), some of which are shown in Fig.1, reveal unusual characteristics in this high redshift (z = 1.534) source. The most striking of these are as follows: 1)The hotspots A and B, and the core C are aligned to within 0″.05 (at the hotspot), as measured on the MERLIN 6 cm map.2)The compact feature in the southern hotspot (A1) has projected dimensions of ~0″.03 x ~0″.015 (see Fig.1d). The corresponding minimum internal energy density of this feature is ≳2.3 × 10−6 erg cm−3.3)There is a continuous zig-zag ridge in the southern component, which starts with a definite spur of emission extending in a south-east direction from the compact feature A1 (see Fig.1b). The magnetic field in A1 is in approximately the same position angle as this spur and the VLBI elongation, which both point towards a bright secondary peak in the southern lobe (1a and 1b).

scholarly journals High-sensitivity radio study of the non-thermal stellar bow shock EB27

2021 ◽  
Author(s):  
Paula Benaglia ◽  
Santiago del Palacio ◽  
Christopher Hales ◽  
Marcelo E Colazo
Keyword(s):  
Radio Emission ◽  
Massive Star ◽  
High Sensitivity ◽  
Bow Shock ◽  
Relativistic Electrons ◽  
Polarimetric Observation ◽  
Very Large Array ◽  
Thermal Radio Emission ◽  
The Magnetic Field ◽  
Linear Polarisation

Abstract We present a deep radio-polarimetric observation of the stellar bow shock EB27 associated to the massive star BD+43○3654. This is the only stellar bow shock confirmed to have non-thermal radio emission. We used the Jansky Very Large Array in S band (2–4 GHz) to test whether this synchrotron emission is polarised. The unprecedented sensitivity achieved allowed us to map even the fainter regions of the bow shock, revealing that the more diffuse emission is steeper and the bow shock brighter than previously reported. No linear polarisation is detected in the bow shock above 0.5%, although we detected polarised emission from two southern sources, probably extragalactic in nature. We modeled the intensity and morphology of the radio emission to better constrain the magnetic field and injected power in relativistic electrons. Finally, we derived a set of more precise parameters for the system EB27–BD+43○3654 using Gaia Early Data Release 3, including the spatial velocity. The new trajectory, back in time, intersects the core of the Cyg OB2 association.

scholarly journals Properties of the inner penumbral boundary and temporal evolution of a decaying sunspot

2018 ◽  
Vol 620 ◽  
pp. A191 ◽  
Author(s):  
M. Benko ◽  
S. J. González Manrique ◽  
H. Balthasar ◽  
P. Gömöry ◽  
C. Kuckein ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Temporal Evolution ◽  
Vertical Component ◽  
Field Vector ◽  
Linear Increase ◽  
Vertical Magnetic Field ◽  
Magnetic Diffusion ◽  
The Magnetic Field ◽  
Linear Decay

Context. It has been empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. Aims. We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28–September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to prove the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots. Methods. A spectral-line inversion technique was used to infer the magnetic field vector from the full-Stokes profiles. In total, eight maps were inverted and the variation of the magnetic properties in time were quantified using linear or quadratic fits. Results. We find a linear decay of the umbral vertical magnetic field, magnetic flux, and area. The penumbra showed a linear increase of the vertical magnetic field and a sharp decay of the magnetic flux. In addition, the penumbral area quadratically decayed. The vertical component of the magnetic field is weaker on the umbra-penumbra boundary of the studied decaying sunspot compared to stable sunspots. Its value seem to be steadily decreasing during the decay phase. Moreover, at any time of the sunspot decay shown, the inner penumbra boundary does not match with a constant value of the vertical magnetic field, contrary to what is seen in stable sunspots. Conclusions. During the decaying phase of the studied sunspot, the umbra does not have a sufficiently strong vertical component of the magnetic field and is thus unstable and prone to be disintegrated by convection or magnetic diffusion. No constant value of the vertical magnetic field is found for the inner penumbral boundary.

scholarly journals Polarization VLBI Observations of a Complete Sample of Northern BL Lacertae Objects

1998 ◽  
Vol 164 ◽  
pp. 165-166
Author(s):  
A. B. Pushkarev ◽  
D. C. Gabuzda
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Synchrotron Emission ◽  
Complete Sample ◽  
Bl Lacertae Objects ◽  
Bl Lacertae ◽  
Vlbi Observations ◽  
Core Components ◽  
Jet Structure ◽  
The Magnetic Field

AbstractThe polarization electric vectors in the VLBI jets of BL Lacertae objects are typically aligned with the jet structure. If the jet radio emission is optically thin synchrotron emission, this implies that the magnetic field is perpendicular to the jet, usually interpreted as a signature of shocks. The distribution of polarization position angles in the VLBI core components appears to be bimodal, with the polarization angles either aligned with or perpendicular to the jet direction. In order to study the origin of this characteristic polarization structure, we have made VLBI polarization observations of all 34 sources in the Kühr and Schmidt sample of BL Lacertae objects.

scholarly journals ANALYTICAL MODEL OF THE PLANETARY BOW SHOCK FOR VARIOUS MAGNETIC FIELD DIRECTIONS BASED ON MHD CALCULATIONS

2020 ◽  
Vol 6 (4) ◽  
pp. 51-58
Author(s):  
Galina Kotova ◽  
Mikhail Verigin ◽  
Tamash Gomboshi ◽  
Konstantin Kabin
Keyword(s):  
Magnetic Field ◽  
Computer Time ◽  
Bow Shock ◽  
Radius Of Curvature ◽  
Dynamic Flow ◽  
Physical Processes ◽  
Downstream Slope ◽  
Mach Numbers ◽  
Semi Empirical ◽  
The Magnetic Field

Study of physical processes in plasma near planets often requires knowledge of the position and shape of the planetary bow shock. Empirical models are usually used since theoretical MHD and kinetic models consume too much computer time and cannot be used to track fast processes. M.I. Verigin proposed a semi-empirical approach based on the use of exact theoretical expressions with a small number of parameters, which have a clear physical meaning. These parameters are estimated by fitting experimental data or detailed MHD calculations. A model of the bow shock near an arbitrary-shaped obstacle has previously been developed for a gas-dynamic flow. This model can be applied to any sonic Mach numbers and large values of the Alfven Mach number. In addition, the asymptotic Mach cone — the angle of inclination of the shock wave at an infinite distance from the planet — has been calculated analytically in the MHD approximation. In this paper, we propose a model of the bow shock for any direction of the magnetic field with respect to the upcoming flow and for any Mach numbers. Parameters of the model are the distance of the nose point from the obstacle, radius of curvature and bluntness of the bow shock at the nose point, a parameter related to the transition to the asymptotic downstream slope of the shock, and a skewing angle appearing when the interplanetary magnetic field is directed at an angle to the solar wind velocity.

Magnetic Field Aligned Potentials as an Acceleration Mechanism at Jupiter

2021 ◽  
Author(s):  
Dave Constable ◽  
Licia Ray ◽  
Sarah Badman ◽  
Chris Arridge ◽  
Chris Lorch ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Temporal Evolution ◽  
Charged Particles ◽  
Uniform Mesh ◽  
Time Varying ◽  
Potential Structure ◽  
Field Aligned Current ◽  
Field Lines ◽  
The Magnetic Field ◽  
Insight Into

&lt;p&gt;Since arriving at Jupiter, Juno has observed instances of field-aligned proton and electron beams, in both the upward and downward current regions. These field-aligned beams are identified by inverted-V structures in plasma data, which indicate the presence of potential structures aligned with the magnetic field. The direction, magnitude and location of these potential structures is important, as it affects the characteristics of any resultant field-aligned current. At high latitudes, Juno has observed potentials of 100&amp;#8217;s of kV occurring in both directions. Charged particles that are accelerated into Jupiter&amp;#8217;s atmosphere and precipitate can excite aurora; likewise, particles accelerated away from the planet can contribute to the population of the magnetosphere.&lt;/p&gt; &lt;p&gt;Using a time-varying 1-D spatial, 2-D velocity space Vlasov code, we examine magnetic field lines which extend from Jupiter into the middle magnetosphere. By applying and varying a potential difference at the ionosphere, we can gain insight into the effect these have on the plasma population, the potential structure, and plasma densities along the field line. Utilising a non-uniform mesh, additional resolution is applied in regions where particle acceleration occurs, allowing the spatial and temporal evolution of the plasma to be examined. Here, we present new results from our model, constrained, and compared with recent Juno observations, and examining both the upward and downward current regions.&lt;/p&gt;

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