Two modes of partially screened gap

Szary, Andrzej; Melikidze, George I.; Gil, Janusz

doi:10.1093/mnras/stu2622

Cited by 56 publications

(56 citation statements)

References 33 publications

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“…This is brought about by the changes in the current flow and the size of the open field line region which might be effective in altering the parameters of the outflowing plasma. The second method leads to modifications in the potential drop across the IAR by introducing the concept of a partially screened gap (PSG, Gil et al 2003;Szary et al 2015). The surface temperature is considered to be at the critical level for the ions to be emitted and in the process reducing the gap potential.…”

Section: Physical Implications Of Nullingmentioning

confidence: 99%

Meterwavelength Single-pulse Polarimetric Emission Survey. III. The Phenomenon of Nulling in Pulsars

Basu

Mitra

Melikidze

2017

ApJ

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116

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A detailed analysis of nulling was conducted for the pulsars studied in the Meterwavelength Single-pulse Polarimetric Emission Survey. We characterized nulling in 36 pulsars including 17 pulsars where the phenomena were reported for the first time. The most dominant nulls lasted for a short duration, less than five periods. The longer duration nulls extending to hundreds of periods were also seen in some cases. A careful analysis showed the presence of periodicities in the transition from the null to the burst states in 11 pulsars. In our earlier work fluctuation spectrum analysis showed multiple periodicities in 6 of these 11 pulsars. We demonstrate that the longer periodicity in each case was associated with nulling. The shorter periodicities usually originate due to subpulse drifting. The nulling periodicities were more aligned with the periodic amplitude modulation indicating a possible common origin for both. Most prevalent nulling lasts for a single period and can be potentially explained using random variations affecting the plasma processes in the pulsar magnetosphere. On the other hand, the longer duration nulls require changes in the pair production processes that need an external triggering mechanism for the change. The presence of periodic nulling puts an added constrain on the triggering mechanism which also needs to be periodic.

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Section: Physical Implications Of Nullingmentioning

confidence: 99%

Meterwavelength Single-pulse Polarimetric Emission Survey. III. The Phenomenon of Nulling in Pulsars

Basu

Mitra

Melikidze

2017

ApJ

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116

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“…Error bars correspond to 1σ. Pulsars: (1) J0108-1431, (2) B0355+54, (3) B0628-28, (4) J0633+1746, (5) B0834+06, (6) B0943+10, (7) B1133+16, (8) B1451-68, (9) B1719-37, (10) B1929+10, (11) J2021+4026, (12) J2043+2740, (13) B2224+65 (see Becker 2009;Szary 2013, and references therein).…”

Section: Observations Of the Polar Capmentioning

confidence: 99%

“…Assuming that the hot spots are actual polar caps heated by backstreaming of ultrarelativistic particles accelerated in the IAR, we can conclude that an actual area of a polar cap, A pc , is considerably smaller than the conventional polar cap area A dp ≈ 6.2 × 10 4 P −1 m 2 (calculated assuming a dipolar configuration of the magnetic field), here P is the pulsar period in seconds. Thus, arXiv:1701.02554v1 [astro-ph.HE] 10 Jan 2017 the surface magnetic field has to be considerably stronger than the dipolar component (see Szary et al 2015, for a detailed description). The possibility to create such field structures at the polar cap surfaces and to maintain them over the typical lifetime of pulsars has been demonstrated recently by Geppert et al (2013);Geppert & Viganò (2014).…”

Section: Introductionmentioning

confidence: 99%

XMM-Newton Observation of the Nearby Pulsar B1133+16

Szary

Gil

Zhang

et al. 2017

ApJ

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We constrain the X-ray properties of the nearby (360 pc), old (5 Myr) pulsar B1133+16 with ∼ 100 ks effective exposure time by XMM-Newton. The observed pulsar flux in the 0.2 − 3 keV energy range is ∼ 10 −14 erg cm −2 s −1 , which results in the recording of ∼ 600 source counts with the EPIC pn and MOS detectors. The X-ray radiation is dominated by nonthermal radiation and is well described by both a single power-law model (PL) and a sum of blackbody and power-law emission (BB+PL). The BB+PL model results in a spectral photon index Γ = 2.4 +0.4 −0.3 and a nonthermal flux in the 0.2 − 3 keV energy range of (7 ± 2) × 10 −15 erg cm −2 s −1 . The thermal emission is consistent with the blackbody emission from a small hot spot with a radius of R pc ≈ 14 +7 −5 m and a temperature of T s = 2.9 +0.6 −0.4 MK. Assuming that the hot spot corresponds to the polar cap of the pulsar, we can use the magnetic flux conservation law to estimate the magnetic field at the surface B s ≈ 3.9 × 10 14 G. The observations are in good agreement with the predictions of the partially screened gap model, which assumes the existence of small-scale surface magnetic field structures in the polar cap region.

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“…Thus, while magnetic spots do form, they are not located at the polar cap and are unlikely to contribute to the slot-gap mechanism. A possible resolution to this puzzle is a complex topology of the magnetosphere where open field lines are connected to a magnetic spot a few kilometers above the stellar surface (Szary et al 2015;Gralla et al 2016). Indeed we notice in Figure 5 that the field lines emerging from the magnetic spots are connected to distant locations on the surface of the star.…”

Section: Plasma Generation and Accelerationmentioning

confidence: 99%

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

Gourgouliatos

Hollerbach

2017

ApJ

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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.

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Two modes of partially screened gap

Cited by 56 publications

References 33 publications

Meterwavelength Single-pulse Polarimetric Emission Survey. III. The Phenomenon of Nulling in Pulsars

Meterwavelength Single-pulse Polarimetric Emission Survey. III. The Phenomenon of Nulling in Pulsars

XMM-Newton Observation of the Nearby Pulsar B1133+16

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

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