Constraints on the Emission Geometries and Spin Evolution of Gamma-Ray Millisecond Pulsars

Johnson, T. J.; Venter, C.; Harding, A. K.; Guillemot, L.; Smith, David A.; Krämer, M.; Çelik, Ö.; Hartog, P. R. den; Ferrara, E. C.; Hou, X.; Landé, J.; Ray, Paul S.

doi:10.1088/0067-0049/213/1/6

Cited by 102 publications

(170 citation statements)

References 148 publications

(376 reference statements)

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“…For example, Muslimov & Harding (2003) give expressions for the slot gap width as a function of P and B, and the width scales linearly with P. When using geometrical models, however, the usual approach is to assume a reasonable value for this width which results in good light curve fits. Our choice of 5% is also supported by the results of Johnson et al (2014) who fit the light curves of 40 γ-ray millisecond pulsars, finding that their best-fit gap width never exceeded 10%, but is usually smaller. Further justification comes from Figure 2 of Muslimov & Harding (2003).…”

mentioning

confidence: 52%

Constraining the geometry of PSR J0855−4644: A nearby pulsar wind nebula with double torus/jet morphology

Maitra

Venter

Acero

2017

A&A

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Aims. PSR J0855−4644 is a fast-spinning, energetic pulsar discovered at radio wavelengths near the south-eastern rim of the supernova remnant RX J0852.0−4622. A follow-up XMM-Newton observation revealed the pulsar's X-ray counterpart and a slightly asymmetric pulsar wind nebula suggesting possible jet structures. Lying at a distance d ≤ 900 pc, PSR J0855−4644 is a pulsar with one of the highestĖ/d 2 from which no GeV γ-ray pulsations have been detected. With a dedicated Chandra observation we aim to further resolve the possible jet structures of the nebula and study the pulsar's geometry in order to understand the lack of γ-ray pulsations. Methods. We perform detailed spatial modelling to constrain the geometry of the pulsar wind nebula and in particular the pulsar's line of sight (observer angle) ζ PSR defined as the angle between the direction of the observer and the pulsar spin axis. We also perform geometric radio and γ-ray light curve modelling using a hollow-cone radio beam model together with two-pole caustic and outer gap models to further constrain ζ PSR and the magnetic obliquity α defined as the angle between the magnetic and spin axes of the pulsar. Results. The Chandra observation reveals that the compact XMM source, thought to be the X-ray pulsar, can be further resolved into a point source surrounded by an elongated axisymmetric nebula with a longitudinal extent of 10 . The pulsar flux represents only ∼ 1% of the XMM compact source and its spectrum is well described by a blackbody of temperature kT = 0.2 keV while the surrounding nebula has a much harder spectrum (Γ = 1.1 for a power-law model). Assuming the origin of the extended emission is from a double torus yields ζ PSR = 32.5 • ± 4.3 • . The detection of thermal X-rays from the pulsar may point to a low value of |ζ − α| if this emission originates from a heated polar cap. Independent constraints from geometric light curve modelling yield α 55 • and ζ 55 • , and 10 • |ζ − α| 30 • . A χ 2 fit to the radio light curve yields a best fit at (α, ζ PSR ) = (22 • , 8 • ), with an alternative fit at (α, ζ PSR ) = (9 • , 25 • ) within 3σ. The lack of non-thermal X-ray emission from the pulsar further supports low values for α and ζ under the assumption that X-rays and γ-rays are generated in the same region of the pulsar magnetosphere. Such a geometry would explain, in the standard caustic pulsar model picture, the radio-loud and γ-ray-quiet behaviour of this highĖ/d 2 pulsar.

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confidence: 52%

Constraining the geometry of PSR J0855−4644: A nearby pulsar wind nebula with double torus/jet morphology

Maitra

Venter

Acero

2017

A&A

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“…It is encouraging that many of the best-fit solutions lie near the ζ inferred from the pulsar wind nebula (PWN) torus fitting [35], notably for the RVD B-field. A significant fraction of fits furthermore lie near the α − ζ diagonal, i.e., they prefer a small impact angle, most probably due to radio visibility constraints [22]. For an isotropic distribution of pulsar viewing angles, one expects ζ values to be distributed as sin(ζ ) between ζ = [0 • , 90 • ], i.e., large ζ values are much more likely than small ζ values, which seems to agree with the large best-fit ζ values we…”

Section: Pos(heasa 2016)042mentioning

confidence: 99%

“…For example, Ng & Romani [34,35] used torus and jet fitting to constrain ζ of a few X-ray pulsars, and obtained a consistent value of ζ = 63.6 +0.07 −0.05 . Johnson et al [22] and Pierbattista et al [37] fitted the radio and γ-ray light curves of millisecond and younger pulsar populations respectively using standard geometric models. DeCesar et al [13] constrained the α and ζ angles of a handful of pulsars using standard emission geometries coupled with the FF B-field.…”

Section: Pos(heasa 2016)042mentioning

confidence: 99%

“…More recent developments include global magnetospheric models such as the force-free (FF) inside and dissipative outside (FIDO) model [24,25], the wind models of, e.g., [36], and particle-in-cell simulations (PIC; [8,9]). Although much progress has been made using these physical (or emission) models, geometric light curve modeling [16,41,42,22,37] still presents a crucial avenue for probing the pulsar magnetosphere in the context of traditional pulsar models. The most commonly used emission geometries include the two-pole caustic (TPC; the SG model may be its physical representation; [15]) and OG models and may be used to constrain the pulsar geometry (i.e., magnetic inclination angle α and the observer viewing angle ζ with respect to the spin axis Ω Ω Ω), as well as the γ-ray emission region's location and extent.…”

Section: Introductionmentioning

confidence: 99%

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High-energy pulsar light curves in an offset polar cap B-field geometry

Barnard¹,

Venter²,

Harding³

2017

Proceedings of 4th Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA 2016)

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The light curves and spectral properties of more than 200 γ-ray pulsars have been measured in unsurpassed detail in the eight years since the launch of the hugely successful Fermi Large Area Telescope (LAT) γ-ray mission. We performed geometric pulsar light curve modelling using static, retarded vacuum, and offset polar cap (PC) dipole B-fields (the latter is characterized by a parameter ε), in conjunction with standard two-pole caustic (TPC) and outer gap (OG) emission geometries. In addition to constant-emissivity geometric models, we also considered a slot gap (SG) E-field associated with the offset-PC dipole B-field and found that its inclusion leads to qualitatively different light curves. We therefore find that the assumed B-field and especially the E-field structure, as well as the emission geometry (magnetic inclination and observer angles), have a great impact on the pulsar's visibility and its high-energy pulse shape. We compared our model light curves to the superior-quality γ-ray light curve of the Vela pulsar (for energies > 100 MeV). Our overall optimal light curve fit (with the lowest χ 2 value) is for the retarded vacuum dipole field and OG model. We found that smaller values of ε are favoured for the offset-PC dipole field when assuming constant emissivity, and larger ε values are favoured for variable emissivity, but not significantly so. When we increased the relatively low SG E-fields we found improved light curve fits, with the inferred pulsar geometry being closer to best fits from independent studies in this case. In particular, we found that such a larger SG E-field (leading to variable emissivity) gives a second overall best fit. This and other indications point to the fact that the actual E-field may be larger than predicted by the SG model.

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“…Nineteen γ-ray and radio MSP light curves in the first Fermi Pulsar Catalog (Abdo et al 2010a) and 40 in the Second Fermi Pulsar Catalog (Abdo et al 2013) were fi t by Johnson (2012) and Johnson et al (2013) respectively. Th ese studies identifi ed three classes of MSP light curves.…”

Section: Light Curve Modelingmentioning

confidence: 99%

Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

Harding¹

2013

Journal of Astronomy and Space Sciences

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Constraints on the Emission Geometries and Spin Evolution of Gamma-Ray Millisecond Pulsars

Cited by 102 publications

References 148 publications

Constraining the geometry of PSR J0855−4644: A nearby pulsar wind nebula with double torus/jet morphology

Constraining the geometry of PSR J0855−4644: A nearby pulsar wind nebula with double torus/jet morphology

High-energy pulsar light curves in an offset polar cap B-field geometry

Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

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