MODELING OF GAMMA-RAY PULSAR LIGHT CURVES USING THE FORCE-FREE MAGNETIC FIELD

Journal Article · Tue Jun 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/715/2/1282· OSTI ID:21450898

Xuening, Bai; Spitkovsky, Anatoly ^[1]

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1. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

Gamma-ray emission from pulsars has long been modeled using a vacuum dipole field. This approximation ignores changes in the field structure caused by the magnetospheric plasma and strong plasma currents. We present the first results of gamma-ray pulsar light-curve modeling using the more realistic field taken from three-dimensional force-free (FF) magnetospheric simulations. Having the geometry of the field, we apply several prescriptions for the location of the emission zone, comparing the light curves to observations. We find that when the emission region is chosen according to the conventional slot-gap (or two-pole caustic) prescription, the model fails to produce double-peak pulse profiles, mainly because the size of the polar cap in the FF magnetosphere is larger than the vacuum field polar cap. This suppresses caustic formation in the inner magnetosphere. The conventional outer-gap model is capable of producing only one peak under general conditions because a large fraction of open field lines does not cross the null charge surface. We propose a novel 'separatrix layer' model, where the high-energy emission originates from a thin layer on the open field lines just inside of the separatrix that bounds the open flux tube. The emission from this layer generates two strong caustics on the sky map due to the effect we term 'Sky Map Stagnation' (SMS). It is related to the fact that the FF field asymptotically approaches the field of a rotating split monopole, and the photons emitted on such field lines in the outer magnetosphere arrive to the observer in phase. The double-peak light curve is a natural consequence of SMS. We show that most features of the currently available gamma-ray pulsar light curves can be reasonably well reproduced and explained with the separatrix layer model using the FF field. Association of the emission region with the current sheet will guide more detailed future studies of the magnetospheric acceleration physics.

• OSTI ID: 21450898
• Journal Information: Astrophysical Journal, Vol. 715, Issue 2; Other Information: DOI: 10.1088/0004-637X/715/2/1282; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
FORCE-FREE MAGNETIC FIELDS
GAMMA RADIATION
MAGNETOHYDRODYNAMICS
PHOTONS
PLASMA
PULSARS
SIMULATION
STARS
THIN FILMS
BOSONS
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
FILMS
FLUID MECHANICS
HYDRODYNAMICS
IONIZING RADIATIONS
MAGNETIC FIELDS
MASSLESS PARTICLES
MECHANICS
RADIATIONS