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.

scholarly journals Solar activity and solar oscillations

1997 ◽  
Vol 181 ◽  
pp. 277-285
Author(s):  
Y. Elsworth
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Radio Emission ◽  
Surface Temperature ◽  
The Sun ◽  
Solar Oscillations ◽  
Thermal Component ◽  
X Ray ◽  
Convective Flows ◽  
Wide Range

Helioseismology provides us with the tools to probe solar activity. So that we can consider how the solar oscillations are influenced by that activity, we first consider the phenomena that we associate with the active Sun. The surface of the Sun is not quiet but shows evidence of convection on a wide range of scales from a few hundred kilometres through to several tens-of-thousands of kilometres. The surface temperature shows signs of the convection structures with the temperature in the bright granules being some 100 K to 200 K hotter than the surrounding dark lanes. Sunspots, which are regions of high magnetic field that suppress convective flows, are clearly visible to even quite crude observations. They are several tens-of-thousands of kilometres in diameter and about 2000 K cooler than their surroundings. Ultraviolet and X-ray pictures from satellites show that the higher layers of the solar atmosphere are very non-uniform with bright regions of high activity. Contemporaneous magnetograms show that these regions are associated with sunspots. Flares - regions of magnetic reconnections - are seen at all wavelengths from X-ray through the visible to radio. They are the non-thermal component of the radio emission of the Sun. There are many other indicators of activity on the Sun.

scholarly journals Joint radio and X-ray modelling of PSR J1136+1551

2019 ◽  
Vol 491 (1) ◽  
pp. 80-91 ◽  
Author(s):  
J Pétri ◽  
D Mitra
Keyword(s):  
Magnetic Dipole ◽  
Thermal Emission ◽  
Essential Feature ◽  
Radio Pulse ◽  
Time Lag ◽  
Polar Cap ◽  
Pulse Profile ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Star Surface

ABSTRACT Multiwavelength observations of pulsar emission properties are powerful means to constrain their magnetospheric activity and magnetic topology. Usually a star centred magnetic dipole model is invoked to explain the main characteristics of this radiation. However, in some particular pulsars where observational constraints exist, such simplified models are unable to predict salient features of their multiwavelength emission. This paper aims to carefully model the radio and X-ray emission of PSR J1136+1551 with an off-centred magnetic dipole to reconcile both wavelength measurements. We simultaneously fit the radio pulse profile with its polarization and the thermal X-ray emission from the polar cap hotspots of PSR J1136+1551. We are able to pin down the parameters of the non-dipolar geometry (which we have assumed to be an offset dipole) and the viewing angle, meanwhile accounting for the time lag between X-ray and radio emission. Our model fits the data if the off-centred magnetic dipole lies about 20 per cent below the neutron star surface. We also expect very asymmetric polar cap shapes and sizes, implying non-antipodal and non-identical thermal emission from the hotspots. We conclude that a non-dipolar surface magnetic field is an essential feature to explain the multiwavelength aspects of PSR J1136+1551 and other similar pulsars.

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 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 Investigating the Magnetospheres of Rapidly Rotating B-type Stars

2016 ◽  
Vol 12 (S329) ◽  
pp. 369-372
Author(s):  
C. L. Fletcher ◽  
V. Petit ◽  
Y. Nazé ◽  
G. A. Wade ◽  
R. H. Townsend ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Centrifugal Force ◽  
Point Of View ◽  
Closed Field ◽  
Theoretical Point ◽  
X Rays ◽  
Rapid Rotation ◽  
X Ray ◽  
Surface Magnetic Field

AbstractRecent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA’s XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

scholarly journals An Emission Line in the Hard X-Ray Spectrum of Hercules X-1: Quantized Cyclotron Emission from the Neutron Star

1977 ◽  
Vol 43 ◽  
pp. 34-34
Author(s):  
W. Pietsch ◽  
C. Reppin ◽  
R. Staubert ◽  
J. Truemper ◽  
W. Voges ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Field Strength ◽  
Second Harmonic ◽  
Narrow Line ◽  
Electron Cyclotron Emission ◽  
Polar Cap ◽  
Astrophysical Application ◽  
X Ray ◽  
Cyclotron Emission

A four hour balloon observation of HERC X-l during the 'On-state' in the 35 day cycle was performed on May 3rd, 1976. The 1.24 second pulsations show a pulsed fraction of 58 ± 8% in the 18-31 KeV interval. A pulsed flux (1.24 sec) was discovered in the 31-88 KeV interval with a pulsed fraction of 51 ± 14%. The spectrum of the pulsed flux can be represented up to 50 KeV by an exponential distribution with KT approximately 8 KeV. At approximately 58 KeV a strong and narrow line feature occurs which we interpret as electron cyclotron emission (ΔN = 1 Landau transition) from the polar cap plasma of the rotating neutron star. The corresponding magnetic field strength is approximately 5 x 1012 Gauss, neglecting gravitational red shift. There is evidence for a second harmonic at approximately 110 KeV (ΔN = 2 ).The astrophysical application of this discovery will be discussed in some detail.

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 Coronal Magnetic Fields of Algol Binaries from Microwave Spectra

1991 ◽  
Vol 130 ◽  
pp. 498-500
Author(s):  
G. Umana ◽  
C. Trigilio ◽  
R. M. Hjellming ◽  
S. Catalano ◽  
M. Rodonò
Keyword(s):  
Magnetic Fields ◽  
Radio Emission ◽  
Mass Exchange ◽  
Thermal Emission ◽  
Magnetic Activity ◽  
Microwave Emission ◽  
X Ray ◽  
Coronal Magnetic Fields ◽  
Hydrodynamic Processes ◽  
Hot Corona

Algol-type binaries are basically known to undergo hydrodynamic processes related to mass exchange between components. Recent observations on radio, X-ray emission and flare-like events have raised the question of possible magnetic activity in the secondary component of these systems (Hall, 1989).From a microwave emission survey we have shown that the radio emission from Algol systems cannot be accounted for by thermal emission from an hot corona (T ≥ 107K) and that their radio luminosities compare very well with those of the magnetically active RS CVn systems (Umana et al., 1990).

scholarly journals A unified accretion-ejection paradigm for black hole X-ray binaries

2019 ◽  
Vol 626 ◽  
pp. A115 ◽  
Author(s):  
G. Marcel ◽  
J. Ferreira ◽  
M. Clavel ◽  
P.-O. Petrucci ◽  
J. Malzac ◽  
...  
Keyword(s):  
Radio Emission ◽  
Accretion Disk ◽  
Ad Hoc ◽  
Emission Model ◽  
X Rays ◽  
Temperature Plasma ◽  
X Ray ◽  
Fitting Procedure ◽  
High Level ◽  
X Ray Binaries

Context. Transient X-ray binaries (XrB) exhibit very different spectral shapes during their evolution. In luminosity-color diagrams, their behavior in X-rays forms q-shaped cycles that remain unexplained. In Paper I, we proposed a framework where the innermost regions of the accretion disk evolve as a response to variations imposed in the outer regions. These variations lead not only to modifications of the inner disk accretion rate ṁin, but also to the evolution of the transition radius rJ between two disk regions. The outermost region is a standard accretion disk (SAD), whereas the innermost region is a jet-emitting disk (JED) where all the disk angular momentum is carried away vertically by two self-confined jets. Aims. In the previous papers of this series, it has been shown that such a JED–SAD disk configuration could reproduce the typical spectral (radio and X-rays) properties of the five canonical XrB states. The aim of this paper is now to replicate all X-ray spectra and radio emission observed during the 2010–2011 outburst of the archetypal object GX 339-4. Methods. We used the two-temperature plasma code presented in two previous papers (Papers II and III) and designed an automatic ad hoc fitting procedure that for any given date calculates the required disk parameters (ṁin,rJ) that fit the observed X-ray spectrum best. We used X-ray data in the 3–40 keV (RXTE/PCA) spread over 438 days of the outburst, together with 35 radio observations at 9 GHz (ATCA) dispersed within the same cycle. Results. We obtain the time distributions of ṁin(t) and rJ(t) that uniquely reproduce the X-ray luminosity and the spectral shape of the whole cycle. In the classical self-absorbed jet synchrotron emission model, the JED–SAD configuration also reproduces the radio properties very satisfactorily, in particular, the switch-off and -on events and the radio-X-ray correlation. Although the model is simplistic and some parts of the evolution still need to be refined, this is to our knowledge the first time that an outburst cycle is reproduced with such a high level of detail. Conclusions. Within the JED–SAD framework, radio and X-rays are so intimately linked that radio emission can be used to constrain the underlying disk configuration, in particular, during faint hard states. If this result is confirmed using other outbursts from GX 339-4 or other X-ray binaries, then radio could be indeed used as another means to indirectly probe disk physics.

Sign in / Sign up

Export Citation Format

Share Document