Formation of a Partially Screened Inner Acceleration Region in Radio Pulsars: Drifting Subpulses and Thermal X‐Ray Emission from Polar Cap Surface

Gil, Janusz; Melikidze, George I.; Zhang, Bing

doi:10.1086/506982

Cited by 29 publications

(31 citation statements)

References 61 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…PSR B0943+10 has also been detected in two short observations with the XMM-Newton observatory as a weak X-ray source (14). Assuming the X-rays to be thermal, this was used to support a model in which one system of streaming particles produces both the sub-pulse-modulated radio emission directly, as well as thermal X-ray emission through bombardment of the polar cap surface (15). Because the particle streams are thought to be determined by the magnetosphere as a whole, detection of simultaneous X-ray/radio mode switching would uniquely probe the interaction between local and global electromagnetic behavior.…”

Section: Main Textmentioning

confidence: 99%

Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

Hermsen

Hessels

Kuiper

et al. 2013

Science

125

121

View full text Add to dashboard Cite

Pulsars emit low-frequency radio waves through to high-energy gamma-rays that are generated anywhere from the surface out to the edges of the magnetosphere. Detecting correlated mode changes in the multi-wavelength emission is therefore key to understanding the physical relationship between these emission sites. Through simultaneous observations, we have detected synchronous switching in the radio and X-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio 'bright' mode, the X-rays show only an un-pulsed, non-thermal component. Conversely, when the pulsar is in a radio 'quiet' mode, the X-ray luminosity more than doubles and a 100%-pulsed thermal component is observed along with the non-thermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories. Main Text:Radio pulsars are powered by the energy released as the highly magnetized neutron star spins down. The radio pulses are generated in the pulsar magnetosphere, most probably close to the neutron star surface (1,2). Shortly after the discovery of pulsars, it was observed that the radio pulse behavior can discretely change on timescales as short as a rotation period. These changes in emission mode can manifest as switches between ordered and disordered states or variations in intensity and pulse shape, including the complete cessation of observable radio emission (3,4).Because the emitted radio luminosity is a negligible fraction of the available spin-down energy, usually substantially less than 10 -5 , this phenomenology was presumed to be related solely to microphysics of the radio emission mechanism itself. This perception has recently been challenged by the identification of a relationship between the spin properties of neutron stars and their radio emission modes. PSR B1931+24 was observed to cease emitting for tens of days, during which it spins down ~50% less rapidly (5). PSR J1841-0500 (6) and PSR J1832+0029 (7) exhibit similar behaviors. A number of other pulsars display smaller changes in spin-down rate, which correlate with variations in their average radio pulse shapes (8). The implication of these results is that mode changing is due to an inherent, perhaps universal pulsar process which causes a sudden change in the rate of angular momentum loss that is communicated along the open field lines of the magnetosphere. Whereas changes in spindown rate can only be detected on time-scales of a few days or longer, the recently identified link with the rapid switching observed in radio emission modes suggests a transformation of the global magnetospheric state in less than a rotation period. Despite the recent flurry of pulsar detections at high energies (9), the only causal relation between the radio pulses and emission at other wavelengths, likely emanating from different locations in the magnetosphere, has been made for optical emission and giant radio pulses from the Crab pulsar (10) PSR B0943+10 is a paragon of mode-changing pul...

show abstract

Section: Main Textmentioning

confidence: 99%

Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

Hermsen

Hessels

Kuiper

et al. 2013

Science

125

121

View full text Add to dashboard Cite

show abstract

“…In a sequence of pulse periods, bands of drifting subpulses have separations P 3 at fixed pulse phase, usually expressed in units of the spin period P. The drift rate is then P 2 /P 3 or, in physical units,φ = P 2 /P 2 P 3 cycles s −1 when P 2 and P are expressed in time units and P 3 in spin periods. A common interpretation is that drifts correspond to E × B motions of multiple particle and radiation beams (a beam "carousel") around a magnetic axis or some other related axis (Ruderman & Sutherland 1975;Deshpande & Rankin 1999;Gil et al 2006;Li et al 2012a). The total time needed for a beam to circulate around the axis is P 4 = 1/φP = P P 3 /P 2 in units of spin periods.…”

Section: Subpulse Drift Modesmentioning

confidence: 99%

Pulsar State Switching From Markov Transitions and Stochastic Resonance

Cordes

2013

ApJ

View full text Add to dashboard Cite

Markov processes are shown to be consistent with metastable states seen in pulsar phenomena, including intensity nulling, pulse-shape mode changes, subpulse drift rates, spin-down rates, and X-ray emission, based on the typically broad and monotonic distributions of state lifetimes. Markovianity implies a nonlinear magnetospheric system in which state changes occur stochastically, corresponding to transitions between local minima in an effective potential. State durations (though not transition times) are thus largely decoupled from the characteristic timescales of various magnetospheric processes. Dyadic states are common but some objects show at least four states with some transitions forbidden. Another case is the long-term intermittent pulsar B1931+24 that has binary radio-emission and torque states with wide, but non-monotonic duration distributions. It also shows a quasi-period of 38 ± 5 days in a 13 yr time sequence, suggesting stochastic resonance in a Markov system with a forcing function that could be strictly periodic or quasi-periodic. Nonlinear phenomena are associated with time-dependent activity in the acceleration region near each magnetic polar cap. The polar-cap diode is altered by feedback from the outer magnetosphere and by return currents from the equatorial region outside the light cylinder that may also cause the neutron star to episodically charge and discharge. Orbital perturbations of a disk or current sheet provide a natural periodicity for the forcing function in the stochastic-resonance interpretation of B1931+24. Disk dynamics may introduce additional timescales in observed phenomena. Future work can test the Markov interpretation, identify which pulsar types have a propensity for state changes, and clarify the role of selection effects.

show abstract

“…The magnetic field at the polar cap region for this process to start is 5×10 13 G, or even higher than that, depending on the curvature radius of the magnetic field in this area (Ruderman & Sutherland 1975;Gil et al 2006;Medin & Lai 2007;Geppert et al 2012). It is evident that this condition does hold for the bulk of the population of neutron stars if their dipole magnetic field is considered, being typically in the range of 10 12 G or lower (Manchester et al 2005).…”

Section: Plasma Generation and Accelerationmentioning

confidence: 99%

“…The slot-gap model and its variants, however, require polar magnetic fields significantly higher than the dipole, with the latter being inferred by pulsar timing and determination of the rotation period P and period derivativė P. According to these measurements, the vast majority of radio emitting pulsars have magnetic fields too weak to power radio emission (Medin & Lai 2007). In this context, it has been argued that appropriate higher multipole components dominate the magnetic field structure near the surface of the star, providing magnetic fields sufficiently strong to power the radiative mechanisms (Gil et al 2006). These strong magnetic fields must be located at the polar cap, the region around the magnetic dipole axis, where open magnetic field lines emerge.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Axis Drift and Magnetic Spot Formation in Neutron Stars with Toroidal Fields

Gourgouliatos

Hollerbach

2017

ApJ

View full text Add to dashboard Cite

We explore magnetic field configurations that lead to the formation of magnetic spots on the surface of neutron stars, and to the displacement of the magnetic dipole axis. We find that a toroidally dominated magnetic field is essential for the generation of a single spot with a strong magnetic field. Once a spot forms, it survives for several million years, even after the total magnetic field has decayed significantly. We find that the dipole axis is not stationary with respect to the neutron star's surface and does not in general coincide with the location of the magnetic spot. This is due to non-axisymmetric instabilities of the toroidal field that displace the poloidal dipole axis at rates that may reach 0.4 • per century. A misaligned poloidal dipole axis with the toroidal field leads to more significant displacement of the dipole axis than the fully aligned case. Finally we discuss the evolution of neutron stars with such magnetic fields on the P− Ṗ diagram and the observational implications. We find that neutron stars spend a very short time before they cross the Death-Line of the P − Ṗ diagram, compared to their characteristic ages. Moreover, the maximum intensity of their surface magnetic field is substantially higher than the dipole component of the field. We argue that SGR 0418+5729 could be an example of this type of behaviour, having a weak dipole field, yet hosting a magnetic spot responsible for its magnetar behaviour. The evolution on the pulse profile and braking index of the Crab pulsar, which are attributed to an increase of its obliquity, are compatible with the anticipated drift of the magnetic axis.

show abstract

Formation of a Partially Screened Inner Acceleration Region in Radio Pulsars: Drifting Subpulses and Thermal X‐Ray Emission from Polar Cap Surface

Cited by 29 publications

References 61 publications

Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

Pulsar State Switching From Markov Transitions and Stochastic Resonance

Magnetic Axis Drift and Magnetic Spot Formation in Neutron Stars with Toroidal Fields

Contact Info

Product

Resources

About