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Article: Gamma-ray luminosity and death lines of pulsars with outer gaps

TitleGamma-ray luminosity and death lines of pulsars with outer gaps
Authors
KeywordsAstronomy physics
Issue Date2004
PublisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205
Citation
Astrophysical Journal Letters, 2004, v. 604 n. 1 I, p. 317-327 How to Cite?
AbstractWe reexamine the outer-gap size by taking the geometry of the dipole magnetic field into account. Furthermore, we also consider that instead of taking the gap size at half of the light cylinder radius to represent the entire outer gap, it is more appropriate to average the entire outer-gap size over the distance. When these two factors are considered, the derived outer-gap size f(P, B, 〈r〉(α)) is a function not only of the period P and magnetic field B of the neutron star but also of the average radial distance to the neutron star, 〈r〉, which depends on the magnetic inclination angle α. We use this new outer-gap model to study the γ-ray luminosity of pulsars, which is given by L γ = f 3(P, B, 〈r〉(α))L sd, where L sd is the pulsar spin-down power, and to study the death lines of γ-ray emission of the pulsars. Our model can predict the γ-ray luminosity of an individual pulsar if its P, B, and α are known. Since different pulsars have different α, this explains why some γ-ray pulsars have very similar P and B but very different γ-ray luminosities. In determining the death line of γ-ray pulsars, we have used a new criterion based on a concrete physical property, i.e., that the fractional size of the outer gap at the null-charge surface for a given pulsar cannot be larger than unity. In an estimate of the fractional size of the outer gap, two possible X-ray fields are considered: (1) X-rays produced by neutron star cooling and polar-cap heating, and (2) X-rays produced by the bombardment of relativistic particles from the outer gap onto the stellar surface (the outer gap is called a "self-sustained outer gap"). Since it is very difficult to measure α in general, we use a Monte Carlo method to simulate the properties of γ-ray pulsars in our Galaxy. We find that this new outer-gap model predicts many more weak γ-ray pulsars, which have a typical age between 0.3 and 3 Myr, than does the old model. For all simulated γ-ray pulsars with self-sustained outer gaps, the γ-ray luminosity L γ satisfies L γ ∝ L sd δ, where the value of δ depends on the sensitivity of the γ-ray detector. For EGRET, δ ∼ 0.38, whereas δ ∼ 0.46 for GLAST. For γ-ray pulsars with L sd ≲ L sd crit, δ ∼ 1, and L sd crit = 1.5 × 10 34P 1/3 ergs s -1 is determined by f (〈r〉 ∼ r L) = 1. These results are roughly consistent with the observed luminosity of γ-ray pulsars. These predictions are very different from those of the previous outer-gap model, which predicts a very flat relation between L γ and L sd.
Persistent Identifierhttp://hdl.handle.net/10722/43413
ISSN
2015 Impact Factor: 5.487
2015 SCImago Journal Rankings: 3.369
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorZhang, Len_HK
dc.contributor.authorCheng, KSen_HK
dc.contributor.authorJiang, ZJen_HK
dc.contributor.authorLeung, Pen_HK
dc.date.accessioned2007-03-23T04:45:13Z-
dc.date.available2007-03-23T04:45:13Z-
dc.date.issued2004en_HK
dc.identifier.citationAstrophysical Journal Letters, 2004, v. 604 n. 1 I, p. 317-327en_HK
dc.identifier.issn2041-8205en_HK
dc.identifier.urihttp://hdl.handle.net/10722/43413-
dc.description.abstractWe reexamine the outer-gap size by taking the geometry of the dipole magnetic field into account. Furthermore, we also consider that instead of taking the gap size at half of the light cylinder radius to represent the entire outer gap, it is more appropriate to average the entire outer-gap size over the distance. When these two factors are considered, the derived outer-gap size f(P, B, 〈r〉(α)) is a function not only of the period P and magnetic field B of the neutron star but also of the average radial distance to the neutron star, 〈r〉, which depends on the magnetic inclination angle α. We use this new outer-gap model to study the γ-ray luminosity of pulsars, which is given by L γ = f 3(P, B, 〈r〉(α))L sd, where L sd is the pulsar spin-down power, and to study the death lines of γ-ray emission of the pulsars. Our model can predict the γ-ray luminosity of an individual pulsar if its P, B, and α are known. Since different pulsars have different α, this explains why some γ-ray pulsars have very similar P and B but very different γ-ray luminosities. In determining the death line of γ-ray pulsars, we have used a new criterion based on a concrete physical property, i.e., that the fractional size of the outer gap at the null-charge surface for a given pulsar cannot be larger than unity. In an estimate of the fractional size of the outer gap, two possible X-ray fields are considered: (1) X-rays produced by neutron star cooling and polar-cap heating, and (2) X-rays produced by the bombardment of relativistic particles from the outer gap onto the stellar surface (the outer gap is called a "self-sustained outer gap"). Since it is very difficult to measure α in general, we use a Monte Carlo method to simulate the properties of γ-ray pulsars in our Galaxy. We find that this new outer-gap model predicts many more weak γ-ray pulsars, which have a typical age between 0.3 and 3 Myr, than does the old model. For all simulated γ-ray pulsars with self-sustained outer gaps, the γ-ray luminosity L γ satisfies L γ ∝ L sd δ, where the value of δ depends on the sensitivity of the γ-ray detector. For EGRET, δ ∼ 0.38, whereas δ ∼ 0.46 for GLAST. For γ-ray pulsars with L sd ≲ L sd crit, δ ∼ 1, and L sd crit = 1.5 × 10 34P 1/3 ergs s -1 is determined by f (〈r〉 ∼ r L) = 1. These results are roughly consistent with the observed luminosity of γ-ray pulsars. These predictions are very different from those of the previous outer-gap model, which predicts a very flat relation between L γ and L sd.en_HK
dc.format.extent818952 bytes-
dc.format.extent12158 bytes-
dc.format.mimetypeapplication/pdf-
dc.format.mimetypetext/plain-
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.rightsThe Astrophysical Journal. Copyright © University of Chicago Press.en_HK
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subjectAstronomy physicsen_HK
dc.titleGamma-ray luminosity and death lines of pulsars with outer gapsen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0004-637X&volume=604&issue=2 pt 1&spage=317&epage=327&date=2004&atitle=Gamma-Ray+Luminosity+and+Death+Lines+of+Pulsars+with+Outer+Gapsen_HK
dc.identifier.emailCheng, KS: hrspksc@hkucc.hku.hken_HK
dc.identifier.authorityCheng, KS=rp00675en_HK
dc.description.naturepublished_or_final_versionen_HK
dc.identifier.doi10.1086/381794en_HK
dc.identifier.scopuseid_2-s2.0-2442540377en_HK
dc.identifier.hkuros85869-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-2442540377&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume604en_HK
dc.identifier.issue1 Ien_HK
dc.identifier.spage317en_HK
dc.identifier.epage327en_HK
dc.identifier.isiWOS:000220301000027-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridZhang, L=38762428100en_HK
dc.identifier.scopusauthoridCheng, KS=9745798500en_HK
dc.identifier.scopusauthoridJiang, ZJ=7404280278en_HK
dc.identifier.scopusauthoridLeung, P=7401749062en_HK

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