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Article: Gamma-ray spectral properties of mature pulsars: A two-layer model

TitleGamma-ray spectral properties of mature pulsars: A two-layer model
Authors
KeywordsMethods: numerical
Pulsars: general
Radiation mechanisms: non-thermal
Issue Date2010
PublisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205
Citation
Astrophysical Journal Letters, 2010, v. 720 n. 1, p. 178-190 How to Cite?
AbstractWe use a simple two-layer outer gap model, whose accelerator consists of a primary region and a screening region, to discuss the γ-ray spectrum of mature pulsars detected by Fermi. By solving the Poisson equation with an assumed simple step-function distribution for the charge density in these two regions, the distribution of the electric field and the curvature radiation process of the accelerated particles can be calculated. In our model, the properties of the phase-averaged spectrum can be completely specified by three gap parameters, i.e., the fractional gap size in the outer magnetosphere, the gap current in the primary region, and the gap size ratio between the primary region and the total gap size. We discuss how these parameters affect the spectral properties. We argue that although the radiation mechanism in the outer gap is a curvature radiation process, the observed gamma-ray spectrum can substantially deviate from the simple curvature spectrum because the overall spectrum consists of two components, i.e., a primary region and a screening region. In some pulsars, the radiation from the screening region is so strong that the photon index from 100 MeV to several GeV can be as flat as ∼2. We show that the fitting fractional gap thickness of the canonical pulsars increases with the spin-down age. We find that the total gap current is about 50% of the Goldreich-Julian value and the thickness of the screening region is a few percent of the total gap thickness. We also find that the predicted γ-ray luminosity is less dependent on the spin-down power (L sd) for pulsars with L sd ≳ 10 36 erg s -1, while the γ-ray luminosity decreases with the spin-down power for pulsars with L sd ≲ 10 36 erg s -1. This relation may imply that the major gap closure mechanism is a photon-photon pair-creation process for pulsars with L sd ≳ 10 36 erg s -1, while it is a magnetic pair-creation process for pulsars with L sd ≲ 10 36 erg s -1. Copyright is not claimed for this article. All rights reserved.
Persistent Identifierhttp://hdl.handle.net/10722/125277
ISSN
2015 Impact Factor: 5.487
2015 SCImago Journal Rankings: 3.369
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorWang, Yen_HK
dc.contributor.authorTakata, Jen_HK
dc.contributor.authorCheng, KSen_HK
dc.date.accessioned2010-10-31T11:21:44Z-
dc.date.available2010-10-31T11:21:44Z-
dc.date.issued2010en_HK
dc.identifier.citationAstrophysical Journal Letters, 2010, v. 720 n. 1, p. 178-190en_HK
dc.identifier.issn2041-8205en_HK
dc.identifier.urihttp://hdl.handle.net/10722/125277-
dc.description.abstractWe use a simple two-layer outer gap model, whose accelerator consists of a primary region and a screening region, to discuss the γ-ray spectrum of mature pulsars detected by Fermi. By solving the Poisson equation with an assumed simple step-function distribution for the charge density in these two regions, the distribution of the electric field and the curvature radiation process of the accelerated particles can be calculated. In our model, the properties of the phase-averaged spectrum can be completely specified by three gap parameters, i.e., the fractional gap size in the outer magnetosphere, the gap current in the primary region, and the gap size ratio between the primary region and the total gap size. We discuss how these parameters affect the spectral properties. We argue that although the radiation mechanism in the outer gap is a curvature radiation process, the observed gamma-ray spectrum can substantially deviate from the simple curvature spectrum because the overall spectrum consists of two components, i.e., a primary region and a screening region. In some pulsars, the radiation from the screening region is so strong that the photon index from 100 MeV to several GeV can be as flat as ∼2. We show that the fitting fractional gap thickness of the canonical pulsars increases with the spin-down age. We find that the total gap current is about 50% of the Goldreich-Julian value and the thickness of the screening region is a few percent of the total gap thickness. We also find that the predicted γ-ray luminosity is less dependent on the spin-down power (L sd) for pulsars with L sd ≳ 10 36 erg s -1, while the γ-ray luminosity decreases with the spin-down power for pulsars with L sd ≲ 10 36 erg s -1. This relation may imply that the major gap closure mechanism is a photon-photon pair-creation process for pulsars with L sd ≳ 10 36 erg s -1, while it is a magnetic pair-creation process for pulsars with L sd ≲ 10 36 erg s -1. Copyright is not claimed for this article. All rights reserved.en_HK
dc.languageengen_HK
dc.publisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205en_HK
dc.relation.ispartofAstrophysical Journal Lettersen_HK
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subjectMethods: numericalen_HK
dc.subjectPulsars: generalen_HK
dc.subjectRadiation mechanisms: non-thermalen_HK
dc.titleGamma-ray spectral properties of mature pulsars: A two-layer modelen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0004-637X&volume=720&spage=178&epage=190&date=2010&atitle=Gamma-ray+spectral+properties+of+mature+pulsars:+A+two-layer+modelen_HK
dc.identifier.emailTakata, J: takata@hku.hken_HK
dc.identifier.emailCheng, KS: hrspksc@hkucc.hku.hken_HK
dc.identifier.authorityTakata, J=rp00786en_HK
dc.identifier.authorityCheng, KS=rp00675en_HK
dc.description.naturepostprint-
dc.identifier.doi10.1088/0004-637X/720/1/178en_HK
dc.identifier.scopuseid_2-s2.0-78149268936en_HK
dc.identifier.hkuros180317en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-78149268936&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume720en_HK
dc.identifier.issue1en_HK
dc.identifier.spage178en_HK
dc.identifier.epage190en_HK
dc.identifier.isiWOS:000281596000016-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridWang, Y=36085420300en_HK
dc.identifier.scopusauthoridTakata, J=22735157300en_HK
dc.identifier.scopusauthoridCheng, KS=9745798500en_HK

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