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Article: A two-dimensional electrodynamical outer gap model for γ-ray pulsars: γ-ray spectrum

TitleA two-dimensional electrodynamical outer gap model for γ-ray pulsars: γ-ray spectrum
Authors
KeywordsGamma-rays: Theory
Pulsars: Individual: Vela pulsar -
Issue Date2006
PublisherBlackwell Publishing Ltd. The Journal's web site is located at http://www.blackwellpublishing.com/journals/MNR
Citation
Monthly Notices Of The Royal Astronomical Society, 2006, v. 366 n. 4, p. 1310-1328 How to Cite?
AbstractA two-dimensional electrodynamical model is used to study particle acceleration in the outer magnetosphere of a pulsar. The charge depletion from the Goldreich-Julian charge density causes a large electric field along the magnetic field lines. The charge particles are accelerated by the electric field and emit γ-rays via the curvature process. Some of the emitted y-rays may collide with X-ray photons to make new pairs, which are accelerated again on the different field lines and emit γ-rays. We simulate the pair creation cascade in the meridional plane using the pair creation mean-free path, in which the X-ray photon number density is proportional to the inverse square of the radial distance. With the space charge density determined by the pair creation simulation, we solve the electric structure of the outer gap in the meridional plane and calculate the curvature spectrum. We investigate in detail the relation between the spectrum and total current, which is carried by the particles produced in the gap and/or injected at the boundaries of the gap. We demonstrate that the hardness of the spectrum is strongly controlled by the current carriers. Especially, the spectrum sharply softens if we assume a larger particle injection at the outer boundary of the outer gap. This is because the mean-free path of the pair creation of the inwardly propagating X-ray photons is much shorter than the light radius, so many pairs are produced in the gap to quench the outer gap. Because the two-dimensional model can link both gap width along the magnetic field line and trans-field thickness with the spectral cut-off energy and flux, we can diagnose both the current through the gap and the inclination angle between the rotational and magnetic axes. We apply the theory to the Vela pulsar. By comparing the results with the Energetic Gamma Ray Experiment Telescope (EGRET) data, we rule out any cases that have a large particle injection at the outer boundary. We also suggest the inclination angle of a^c ^ 65°. The present model predicts the outer gap starting from near the conventional null charge surface for the Vela pulsar. j © 2006 RAS.
Persistent Identifierhttp://hdl.handle.net/10722/134626
ISSN
2015 Impact Factor: 4.952
2015 SCImago Journal Rankings: 2.806
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorTakata, Jen_HK
dc.contributor.authorShibata, Sen_HK
dc.contributor.authorHirotani, Ken_HK
dc.contributor.authorChang, HKen_HK
dc.date.accessioned2011-06-29T08:04:48Z-
dc.date.available2011-06-29T08:04:48Z-
dc.date.issued2006en_HK
dc.identifier.citationMonthly Notices Of The Royal Astronomical Society, 2006, v. 366 n. 4, p. 1310-1328en_HK
dc.identifier.issn0035-8711en_HK
dc.identifier.urihttp://hdl.handle.net/10722/134626-
dc.description.abstractA two-dimensional electrodynamical model is used to study particle acceleration in the outer magnetosphere of a pulsar. The charge depletion from the Goldreich-Julian charge density causes a large electric field along the magnetic field lines. The charge particles are accelerated by the electric field and emit γ-rays via the curvature process. Some of the emitted y-rays may collide with X-ray photons to make new pairs, which are accelerated again on the different field lines and emit γ-rays. We simulate the pair creation cascade in the meridional plane using the pair creation mean-free path, in which the X-ray photon number density is proportional to the inverse square of the radial distance. With the space charge density determined by the pair creation simulation, we solve the electric structure of the outer gap in the meridional plane and calculate the curvature spectrum. We investigate in detail the relation between the spectrum and total current, which is carried by the particles produced in the gap and/or injected at the boundaries of the gap. We demonstrate that the hardness of the spectrum is strongly controlled by the current carriers. Especially, the spectrum sharply softens if we assume a larger particle injection at the outer boundary of the outer gap. This is because the mean-free path of the pair creation of the inwardly propagating X-ray photons is much shorter than the light radius, so many pairs are produced in the gap to quench the outer gap. Because the two-dimensional model can link both gap width along the magnetic field line and trans-field thickness with the spectral cut-off energy and flux, we can diagnose both the current through the gap and the inclination angle between the rotational and magnetic axes. We apply the theory to the Vela pulsar. By comparing the results with the Energetic Gamma Ray Experiment Telescope (EGRET) data, we rule out any cases that have a large particle injection at the outer boundary. We also suggest the inclination angle of a^c ^ 65°. The present model predicts the outer gap starting from near the conventional null charge surface for the Vela pulsar. j © 2006 RAS.en_HK
dc.languageeng-
dc.publisherBlackwell Publishing Ltd. The Journal's web site is located at http://www.blackwellpublishing.com/journals/MNRen_HK
dc.relation.ispartofMonthly Notices of the Royal Astronomical Societyen_HK
dc.rightsThe definitive version is available at www.blackwell-synergy.com-
dc.subjectGamma-rays: Theoryen_HK
dc.subjectPulsars: Individual: Vela pulsar -en_HK
dc.titleA two-dimensional electrodynamical outer gap model for γ-ray pulsars: γ-ray spectrumen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0035-8711&volume=366&issue=4&spage=1310&epage=1328&date=2006&atitle=A+two-dimensional+electrodynamical+outer+gap+model+for+γ-ray+pulsars:+γ-ray+spectrum-
dc.identifier.emailTakata, J: takata@hku.hken_HK
dc.identifier.authorityTakata, J=rp00786en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1111/j.1365-2966.2006.09904.xen_HK
dc.identifier.scopuseid_2-s2.0-33644601079en_HK
dc.identifier.hkuros170784-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-33644601079&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume366en_HK
dc.identifier.issue4en_HK
dc.identifier.spage1310en_HK
dc.identifier.epage1328en_HK
dc.identifier.isiWOS:000235696500012-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridTakata, J=22735157300en_HK
dc.identifier.scopusauthoridShibata, S=7402120464en_HK
dc.identifier.scopusauthoridHirotani, K=7003960035en_HK
dc.identifier.scopusauthoridChang, HK=7407523188en_HK
dc.identifier.citeulike526599-

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