scholarly journals A single spark model for PSR J2144−3933

2019 ◽  
Vol 492 (2) ◽  
pp. 2468-2480 ◽  
Author(s):  
Dipanjan Mitra ◽  
Rahul Basu ◽  
George I Melikidze ◽  
Mihir Arjunwadkar
Keyword(s):  
Magnetic Field ◽  
Critical Temperature ◽  
Single Pulse ◽  
Single Component ◽  
Gap Model ◽  
Acceleration Region ◽  
Polar Cap ◽  
Surface Magnetic Field ◽  
Gap Models ◽  
Vacuum Gap

ABSTRACT The partially screened vacuum gap model (PSG) for the inner acceleration region in normal radio pulsars, a variant of the pure vacuum gap model, attempts to account for the observed thermal X-ray emission from polar caps and the subpulse drifting time-scales. We have used this model to explain the presence of death lines and extreme location of PSR J2144−3933 in the $P{-}\dot{P}$ diagram. This model requires maintaining the polar cap near a critical temperature and the presence of non-dipolar surface magnetic field to form the inner acceleration region. In the PSG model, thermostatic regulation is achieved by sparking discharges, which are a feature of all vacuum gap models. We demonstrate that non-dipolar surface magnetic field reduces polar cap area in PSR J2144−3933 such that only one spark can be produced and is sufficient to sustain the critical temperature. This pulsar has a single-component profile over a wide frequency range. Single-pulse polarimetric observations and the rotating vector model confirm that the observer’s line of sight traverses the emission beam centrally. These observations are consistent with a single spark operating within framework of the PSG model leading to single-component emission. Additionally, single-pulse modulations of this pulsar, including lack of subpulse drifting, presence of single-period nulls and microstructure, are compatible with a single spark either in PSG or in general vacuum gap models.

Braneworld effects in plasma magnetosphere of a slowly rotating magnetized neutron star

2019 ◽  
Vol 28 (10) ◽  
pp. 1950128 ◽  
Author(s):  
Javlon Rayimbaev ◽  
Bobur Turimov ◽  
Bobomurat Ahmedov
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Charge Density ◽  
Production Condition ◽  
Scalar Potential ◽  
Polar Cap ◽  
Radiation Beam ◽  
Electrical Fields ◽  
Analytical Expression ◽  
Surface Magnetic Field

Results of our previous paper [B. V. Turimov, B. J. Ahmedov and A. A. Hakimov, Phys. Rev. D 96 (2017) 104001] show that the effects of brane charges are not negligible in the magnetic field of the magnetized neutron star, in particular at the surface of the star, and increasing the value of brane tidal charges causes an increases in the value of surface magnetic field of magnetized neutron star, that is why it is important to consider the effects of braneworlds on energetic processes in the plasma magnetosphere of the neutron star. In this paper, we have obtained the analytical expression for Goldreich–Julian (GJ) charge density in braneworlds for inclined neutron star by solving Maxwell’s equations and found that the value of GJ charge density decreases in braneworlds. The analytical expression for scalar potential in the polar cap region of the neutron star has also been obtained. It is shown that the values of the parallel accelerating electrical fields increase with the increase of the value of the tidal charge near the surface of the neutron star. The influence of braneworlds on pair production condition on the surface of the neutron star and magnetospheric energy losses due to electromagnetic radiations have also been studied. We have shown how radiation beam becomes narrow due to the effects of braneworlds by studying the particle’s trajectory in the polar cap region in the [Formula: see text]–[Formula: see text] ([Formula: see text].) plane. Numerical calculations for particle motion in the polar cap region show that accelerating distance of charged particle increases up to its maximum value in braneworld in comparison with that in GR, due to additional gravitating behavior of tidal charges.

scholarly journals Observational Consequences of Polar Cap Theories

1981 ◽  
Vol 95 ◽  
pp. 99-102
Author(s):  
Andrew F. Cheng
Keyword(s):  
Magnetic Field ◽  
Temporal Modulation ◽  
Polar Cap ◽  
Ion Outflow ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Polar Caps ◽  
Temperature Oscillations ◽  
Field Lines ◽  
Positive Ion

Possible observational consequences are outlined for pulsar models with positive ion outflow at the polar caps together with e+-e− pair production discharge there. A characteristic thermal x-ray luminosity is maintained by discharge heating in regions of positive current outflow. A decrease in polar cap thermal x-ray emission may occur during radio nulls. Two mechanisms are identified which can yield temporal modulation of the outflowing ion and e+-e− plasmas, and which may lead to modulation of coherent radio emission on observed microstructure timescales. These are: (1) polar cap temperature oscillations which occur preferentially in pulsars of low surface magnetic field, and (2) the tendency of sparks to migrate toward the convex side of the magnetic field lines.

scholarly journals Pulsars with Strong Magnetic Fields: Polar Gaps, Bound Pair Creation and Nonthermal Luminosities

1995 ◽  
Vol 48 (4) ◽  
pp. 571 ◽  
Author(s):  
VV Usov ◽  
DB Melrose
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Thermionic Emission ◽  
Pair Creation ◽  
Radio Pulsars ◽  
Polar Cap ◽  
Polar Gap ◽  
Gap Models ◽  
The Magnetic Field ◽  
Frequency Radiation

Modifications to polar-gap models for pulsars are discussed for the case where the surface magnetic field, Bs, of the neutron star is strong. For B ~ 4 X 108 T, the curvature ,-quanta emitted tangentially to the curved force lines of the magnetic field are captured near the threshold of bound pair creation and are channelled along the magnetic field as bound electron-positron pairs (positronium). The stability of such bound pairs against ionization by the parallel electric field,. Ell' in the polar cap, and against photoionization is discussed. Unlike free pairs, bound pairs do not screen Ell near the neutron star. As a consequence, the energy flux in highly relativistic particles and high-frequency (X-ray and/or ,-ray) radiation from the polar gaps can be much greater than in the absence of positronium formation. We discuss this enhancement for (a) Arons-type models, in which particles flow freely from the surface, and find any enhancement to be modest, and (b) Ruderman-Sutherland-type models, in which particles are tightly bound to the surface, and find that the enhancement can be substantial. In the latter case we argue for a self-consistent model in which partial screening of Ell maintains it close to the threshold value for field ionization of the bound pairs, and in which a reverse flux of accelerated particles maintains the polar cap at a temperature such that thermionic emission supplies the particles needed for this screening. This model applies only in a restricted range of periods, P2 < P < PI, and it implies an energy flux in high-energy particles that can correspond to a substantial fraction of the spin-down power of the pulsar. Nonthermal, high-frequency radiation has been observed from six radio pulsars and Geming is usually included as a seventh case. The nonthermal luminosity can be higher than can be explained in terms of conventional polar-gap and outer-gap models. The self-consistent polar-gap model proposed here alleviates this difficulty, provided the magnetic field satisfies B ;G 4 X 108 T (which is so for five of these pulsars, and plausibly for the other two if a modest nondipolar component is assumed), and the surface temperature (in the absence of heating by the reverse flux) satisfies T; ;S 0 .5 X 106 K, so that thermionic emission from the surface is unimportant. It is argued that sufficient power is available to explain the observed high-frequency radiation of most of these pulsars. However, the Crab and PSR 0540-69 have periods P < P2, and we suggest that an outer-gap model is more appropriate for these. Our model implies a death line at P = PI "-J 0�5 s for B ;G 4 X 108 T, and we speculate on why, nevertheless, radio pulsars with strong fields are found at P > Pl.

scholarly journals Evaluating the evidence of multipolar surface magnetic field in PSR J0108–1431

2019 ◽  
Vol 489 (4) ◽  
pp. 4589-4605 ◽  
Author(s):  
Prakash Arumugasamy ◽  
Dipanjan Mitra
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Thermal Emission ◽  
Emission Peak ◽  
Emission Model ◽  
Polar Cap ◽  
Thermal Component ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Photon Index

ABSTRACT PSR J0108–1431 is an old pulsar where the X-ray emission is expected to have a thermal component from the polar cap and a non-thermal component from the magnetosphere. Although the phase-integrated spectra are fit best with a single non-thermal component modelled with a power law (PL) of photon index Γ = 2.9, the X-ray pulse profiles do show the presence of phase-separated thermal and non-thermal components. The spectrum extracted from half the rotational phase away from the X-ray peak fits well with either a single blackbody (BB) or a neutron star atmosphere (NA) model, whereas the spectrum from the rest of the phase range is dominated by a PL. From Bayesian analysis, the estimated BB area is smaller than the expected polar cap area for a dipolar magnetic field with a probability of 86 per cent, whereas the area estimate from the NA model is larger with a probability of 80 per cent. Due to the ambiguity in the thermal emission model, the polar cap area cannot be reliably estimated and hence cannot be used to understand the nature of the surface magnetic field. Instead, we can infer the presence of multipolar magnetic field from the misalignment between the pulsar’s thermal X-ray peak and the radio emission peak. For J0108–1431, we estimated a phase-offset Δϕ > 0.1 between the thermal polar cap emission peak and the radio emission peak and argue that this is best explained by the presence of a multipolar surface magnetic field.

Particle acceleration and electromagnetic field of deformed neutron stars

2019 ◽  
Vol 35 (09) ◽  
pp. 2050056 ◽  
Author(s):  
Javlon Rayimbaev ◽  
Bobur Turimov ◽  
Figueroa Marcos ◽  
Satimbay Palvanov ◽  
Azamkhan Rakhmatov
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Neutron Star ◽  
Neutron Stars ◽  
Electromagnetic Fields ◽  
Deformation Parameter ◽  
Radio Pulsar ◽  
Slow Rotation ◽  
Polar Cap ◽  
Surface Magnetic Field

Neutron stars (NS)s are astrophysical objects with strong gravitational and electromagnetic fields. Since there are several effects on radiation processes around the star, it is impossible to consider whole effects all together. One way to study the processes is by considering them one by one as a toy model. In this paper, we have investigated the effects of spacetime deformation on the surface magnetic field of the slowly rotating neutron star and its plasma magnetospheric processes, such as the plasma magnetosphere formation around the star. At first, the approximate vacuum solutions of the Maxwell equations for the electromagnetic fields of a magnetized neutron star in a slowly rotating deformed spacetime metric have been obtained. It has been shown that the positive deformation parameter leads to an increase in the value of the (surface) magnetic field at the near zone of the neutron star, while the effect of the negative deformation parameter is vice versa. We have also considered the electric field of the slowly rotating neutron star in the spacetime. In the slow rotation approximation, we have studied the particle acceleration in the polar cap zone, considering the effect of deformation of spacetime on the [Formula: see text]-Lorentz factor of a relativistic charged particle. It is shown that in the case of the positive deformation, an additional gravity occurs around the NS. The effects of spacetime deformation on magneto-dipolar radiation of radio pulsars and polar cap size have also been studied and shown that negative deformation of spacetime increased the radiation luminosity and as positive deformation increases, the luminosity decreases. Size of polar cap region of a neutron star, where magnetic field lines open, increases with increasing the value of the deformation parameter [Formula: see text]. Moreover, we have studied the influence of the spacetime deformation on the death line for radio pulsar, which separates the region in [Formula: see text] [Formula: see text] diagram, where the pulsar can or cannot radiate in radio band (create pair production) through inverse compton scattering (ICS). It is shown that the negative (positive) deformation shifts upward (downward) the death line, which means that even a small negative (positive) deformation of spacetime may cause to be radio-quite (be radio load) the radio pulsar which is lying on the death line (in [Formula: see text] diagram) in the GR frame with its corresponding parameters.

scholarly journals Surface magnetic fields in pulsars

2008 ◽  
Vol 4 (S259) ◽  
pp. 131-132
Author(s):  
George I. Melikidze ◽  
Janusz Gil
Keyword(s):  
Magnetic Field ◽  
Hot Spot ◽  
Black Body ◽  
Small Scale ◽  
Radio Pulsars ◽  
Polar Cap ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Bolometric Luminosity ◽  
Polar Caps

AbstractObservations of hot-spot thermal X-ray emission from radio pulsars implicate that surface magnetic field (SMF) at the polar cap is much stronger than the conventional dipolar component estimated from the pulsar spin-down. This strongly suggests that SMF is dominated by the crust anchored small scale magnetic field. We present the observed values of black body temperature and bolometric luminosity of X-ray emission from hot polar caps of a number of pulsars. In all cases the inferred value of SMF is close to 1014 G.

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 The Nature of the Chemical Anomalies of the Sirius A

1998 ◽  
Vol 11 (1) ◽  
pp. 391-391
Author(s):  
V. Leushin
Keyword(s):  
Magnetic Field ◽  
Oscillator Strengths ◽  
Helium Abundance ◽  
Surface Magnetic Field ◽  
Line Widths ◽  
Chemical Anomalies ◽  
Improved Accuracy

On the basis of the analysis of the observed equivalent line widths of FeI, FeII, and TiII in the spectra of Sirius A and Omicron Peg and calculation of abundances of these elements, the oscillator strengths of the lines used are refined. With the improved oscillator strengths, the iron and titanium abundances in the atmosphere of Sirius A are obtained with a higher accuracy than previously: lgN(FeI) = 7.899 ±0.011, lgN(FeII) = 7.908±0.010, lgN(TiII) =5.30±0.02. The improved accuracy allowed one to conclude that the surface magnetic field is absent in the atmosphere of Sirius A: H =3D 0±100 Gs. The equivalent widths of 7 helium lines of the red region of the spectrum are measured. The calculations of these lines (with allowance for their blending with lines of other elements) show normal helium abundance. Following a comparison of features of Sirius A and Omicron Peg, a suggestion is advanced on possible reasons for the existence of Am stars.

scholarly journals The effects of surface fossil magnetic fields on massive star evolution: III. The case of τ Sco

2021 ◽  
Author(s):  
Z Keszthelyi ◽  
G Meynet ◽  
F Martins ◽  
A de Koter ◽  
A David-Uraz
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Massive Star ◽  
Slow Rotation ◽  
Single Star ◽  
Surface Magnetic Field ◽  
Fundamental Parameters ◽  
Chemical Enrichment ◽  
Star Models ◽  
Nitrogen Excess

Abstract τ Sco, a well-studied magnetic B-type star in the Uτer Sco association, has a number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface magnetic field is much more complex than a purely dipolar configuration which is unusual for a magnetic massive star. We employ the cmfgen radiative transfer code to determine the fundamental parameters and surface CNO and helium abundances. Then, we employ mesa and genec stellar evolution models accounting for the effects of surface magnetic fields. To reconcile τ Sco’s properties with single-star models, an increase is necessary in the efficiency of rotational mixing by a factor of 3 to 10 and in the efficiency of magnetic braking by a factor of 10. The spin down could be explained by assuming a magnetic field decay scenario. However, the simultaneous chemical enrichment challenges the single-star scenario. Previous works indeed suggested a stellar merger origin for τ Sco. However, the merger scenario also faces similar challenges as our magnetic single-star models to explain τ Sco’s simultaneous slow rotation and nitrogen excess. In conclusion, the single-star channel seems less likely and versatile to explain these discrepancies, while the merger scenario and other potential binary-evolution channels still require further assessment as to whether they may self-consistently explain the observables of τ Sco.

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