scholarly journals The influence of small-scale magnetic field on the heating of J0250+5854 polar cap

2021 ◽  
Vol 2103 (1) ◽  
pp. 012034
Author(s):  
D P Barsukov ◽  
A A Matevosyan ◽  
I K Morozov ◽  
A N Popov ◽  
M V Vorontsov
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Bound State ◽  
Small Scale ◽  
Polar Cap ◽  
Electron Positron ◽  
Curvature Radiation ◽  
Cap Model ◽  
Star Surface ◽  
Primary Electrons

Abstract The influence of surface small-scale magnetic field on the heating of PSR J0250+5854 polar cap is considered. It is assumed that the polar cap is heated only by reverse positrons accelerated in pulsar diode. It is supposed that pulsar diode is located near the star surface (polar cap model) and operates in the steady state space charge-limited flow regime. The reverse positron current is calculated in the framework of two models: rapid and gradually screening. To calculate the production rate of electron-positron pairs we take into account only the curvature radiation of primary electrons and its absorption in magnetic field. It is assumed that some fraction of electron-positron pairs may be created in bound state that can later be photoionized by thermal photons from star surface.

scholarly journals Rapid Modification of Neutron Star Surface Magnetic Field: A proposed mechanism for explaining Radio Emission State Changes in Pulsars

2021 ◽  
Author(s):  
U Geppert ◽  
R Basu ◽  
D Mitra ◽  
G I Melikidze ◽  
M Szkudlarek
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Temperature Gradients ◽  
Local Magnetic Field ◽  
Small Scale ◽  
Polar Cap ◽  
Thermoelectric Effects ◽  
Surface Magnetic Field ◽  
State Changes ◽  
Star Surface

Abstract The radio emission in many pulsars show sudden changes, usually within a period, that cannot be related to the steady state processes within the inner acceleration region (IAR) above the polar cap. These changes are often quasi-periodic in nature, where regular transitions between two or more stable emission states are seen. The durations of these states show a wide variety ranging from several seconds to hours at a time. There are strong, small scale magnetic field structures and huge temperature gradients present at the polar cap surface. We have considered several processes that can cause temporal modifications of the local magnetic field structure and strength at the surface of the polar cap. Using different magnetic field strengths and scales, and also assuming realistic scales of the temperature gradients, the evolutionary timescales of different phenomena affecting the surface magnetic field was estimated. We find that the Hall drift results in faster changes in comparison to both Ohmic decay and thermoelectric effects. A mechanism based on the Partially Screened Gap (PSG) model of the IAR has been proposed, where the Hall and thermoelectric oscillations perturb the polar cap magnetic field to alter the sparking process in the PSG. This is likely to affect the observed radio emission resulting in the observed state changes.

scholarly journals PARTICLE ACCELERATION, MAGNETIC FIELD GENERATION, AND ASSOCIATED EMISSION IN COLLISIONLESS RELATIVISTIC JETS

2008 ◽  
Vol 17 (10) ◽  
pp. 1761-1767 ◽  
Author(s):  
K.-I. NISHIKAWA ◽  
Y. MIZUNO ◽  
G. J. FISHMAN ◽  
P. HARDEE
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Small Scale ◽  
Spectral Structure ◽  
Relativistic Jets ◽  
Weibel Instability ◽  
Electron Positron ◽  
Jitter Radiation

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electron-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electrons' transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties to synchrotron radiation which assumes a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

scholarly journals Emission of particles and photons in the pulsar polar cap

2000 ◽  
Vol 177 ◽  
pp. 473-478
Author(s):  
A. I. Tsygan
Keyword(s):  
Gamma Ray ◽  
Radio Pulsars ◽  
Polar Cap ◽  
X Ray ◽  
Polar Caps ◽  
Electron Positron ◽  
Inertial Frames ◽  
General Relativistic ◽  
Star Surface ◽  
General Relativistic Effect

AbstractWe study emission of particles and photons from a pulsar polar cap. The Goldreich-Julian model for the regime of free emission of charged particles from the neutron star surface is used. In this case the electric field is generated due to the general relativistic effect of dragging of inertial frames. The spectra and shapes of gamma-ray pulses, the parameters of the electron-positron plasma and the intensity of X-ray emission from hot spots in the polar region of radio pulsars are discussed. The effect of non-dipole magnetic field on X-ray emission of polar caps is considered. It is shown that the increase of magnetic line curvature leads to much smaller temperatures and X-ray luminosities of the polar caps as compared with the purely dipole field.

scholarly journals Storm-time related mass density anomalies in the polar cap as observed by CHAMP

2010 ◽  
Vol 28 (1) ◽  
pp. 165-180 ◽  
Author(s):  
R. Liu ◽  
H. Lühr ◽  
S.-Y. Ma
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Storms ◽  
Mass Density ◽  
Small Scale ◽  
Polar Cap ◽  
Ion Outflow ◽  
The North ◽  
Scale Field ◽  
Density Enhancement ◽  
The Magnetic Field

Abstract. Strong and localized thermospheric mass density events are observed in the polar cap region by the CHAMP satellites at about 400 km altitude during geomagnetic storms. During the 4 years considered (2002–2005) 29 storms with Dst<−100 nT occurred, in 90% of them polar cap density anomalies were detected. Based on the altogether 56 anomaly events a statistical analysis was performed. The anomalies are of medium scale (500–1500 km) and seem to have a short dwell-time (<1.5 h) in the polar cap. The relative density enhancement is found to range around 2 in both hemispheres. The peak density is in the Northern Hemisphere by a factor of 1.4 larger than in the southern. Also the number of detected events in the north is twice as large as that in the south (37 vs. 19). Mass density anomalies in the polar cap occur under all interplanetary magnetic field (IMF) directions. Numerous strong anomalies have been detected in positive and negative IMF Bz conditions when the magnetic field strength is above 5 nT. Rather few events occurred for small |Bz| (<5 nT) or for positive Bz combined with vanishing By. Some of the density anomalies are accompanied by intensive small-scale field-aligned currents (FACs). But about as many show no relation to FACs. If FACs are present there, the current density is believed to be correlated with the strength of the IMF Bz. Although this paper concentrates on the presentation of the observations, we show for one event that the ion outflow mechanism could be responsible for the mass density anomalies in the polar cap.

Correction to “Polar cap bifurcation during steady-state northward interplanetary magnetic field with ∣BY∣ ∼BZ”

2007 ◽  
Vol 112 (A12) ◽  
pp. n/a-n/a
Author(s):  
Masakazu Watanabe ◽  
George J. Sofko ◽  
Dieter A. André ◽  
Takashi Tanaka ◽  
Marc R. Hairston
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Interplanetary Magnetic Field ◽  
Polar Cap

scholarly journals On a Possible Mechanism of Pulsar Radiation

1992 ◽  
Vol 128 ◽  
pp. 232-235 ◽  
Author(s):  
A. Z. Kazbegi ◽  
G. Z. Machabeli ◽  
G. I. Melikidze
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Electric Field ◽  
Lorentz Factor ◽  
Stellar Surface ◽  
Polar Regions ◽  
Electron Positron ◽  
Pulsar Radiation ◽  
Beam Parameters ◽  
Primary Electrons

At present there exist several well-grounded models of pulsar radiation which do not exactly coincide with each other [e.g. Ruderman and Sutherland (1975), Cheng and Ruderman (1980), Arons and Sharlemann (1979), Arons (1981)]. The creation of a dense, relativistic, electron-positron plasma in the polar regions of rotating neutron star magnetospheres is the point of similarity between these models. Surely the pulsar radiation should be generated in such a plasma. The plasma density near the stellar surface is np ≃ 1016 e to 1017cm–3, and the average Lorentz-factor of the particles is γp = 3 to 10. The plasma is penetrated by the beam of “primary” electrons, extracted from the stellar surface and accelerated by the electric field. The beam parameters are as follows: nb = 7 x 10–2B0P–1, where P is the pulsar period and B0 magnetic field at the stellar surface and γb = 3 x 106 to 107.

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