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Title: Light-curve modelling constraints on the obliquities and aspect angles of the young Fermi pulsars

Abstract

In more than four years of observation the Large Area Telescope on board the Fermi satellite has identified pulsed γ-ray emission from more than 80 young or middle-aged pulsars, in most cases providing light curves with high statistics. Fitting the observed profiles with geometrical models can provide estimates of the magnetic obliquity α and of the line of sight angle ζ, yielding estimates of the radiation beaming factor and radiated luminosity. Using different γ-ray emission geometries (Polar Cap, Slot Gap, Outer Gap, One Pole Caustic) and core plus cone geometries for the radio emission, we fit γ-ray light curves for 76 young or middle-aged pulsars and we jointly fit their γ-ray plus radio light curves when possible. We find that a joint radio plus γ-ray fit strategy is important to obtain (α,ζ) estimates that can explain simultaneously detectable radio and γ-ray emission: when the radio emission is available, the inclusion of the radio light curve in the fit leads to important changes in the (α,ζ) solutions. The most pronounced changes are observed for Outer Gap and One Pole Caustic models for which the γ-ray only fit leads to underestimated α or ζ when the solution is found to the leftmore » or to the right of the main α-ζ plane diagonal respectively. The intermediate-to-high altitude magnetosphere models, Slot Gap, Outer Gap, and One pole Caustic, are favoured in explaining the observations. We find no apparent evolution of α on a time scale of 106 years. For all emission geometries our derived γ-ray beaming factors are generally less than one and do not significantly evolve with the spin-down power. A more pronounced beaming factor vs. spin-down power correlation is observed for Slot Gap model and radio-quiet pulsars and for the Outer Gap model and radio-loud pulsars. The beaming factor distributions exhibit a large dispersion that is less pronounced for the Slot Gap case and that decreases from radio-quiet to radio-loud solutions. For all models, the correlation between γ-ray luminosity and spin-down power is consistent with a square root dependence. The γ-ray luminosities obtained by using the beaming factors estimated in the framework of each model do not exceed the spin-down power. This suggests that assuming a beaming factor of one for all objects, as done in other studies, likely overestimates the real values. The data show a relation between the pulsar spectral characteristics and the width of the accelerator gap. Furthermore, the relation obtained in the case of the Slot Gap model is consistent with the theoretical prediction.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [7]
  1. Nicolaus Copernicus Astronomical Center, Torun (Poland); INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, Milano (Italy); Univ. Paris Diderot, Paris Cedex (France)
  2. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  3. Univ. Paris Diderot, Gif sur Yvette (France); Institut Univ. de France (France)
  4. National Academy of Sciences, Washington, D.C. (United States); Naval Research Lab., Washington, D.C. (United States)
  5. INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, Milano (Italy); Istituto Nazionale di Fisica Nucleare, Pavia (Italy)
  6. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.
  7. Hope College, Holland, MI (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1355164
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Astronomy and Astrophysics
Additional Journal Information:
Journal Volume: 575; Journal ID: ISSN 0004-6361
Publisher:
EDP Sciences
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; stars: neutron; pulsars: general; gamma rays: stars; radiation mechanisms: non-thermal; methods: statistical

Citation Formats

Pierbattista, M., Harding, A. K., Grenier, I. A., Johnson, T. J., Caraveo, P. A., Kerr, M., and Gonthier, P. L. Light-curve modelling constraints on the obliquities and aspect angles of the young Fermi pulsars. United States: N. p., 2015. Web. doi:10.1051/0004-6361/201423815.
Pierbattista, M., Harding, A. K., Grenier, I. A., Johnson, T. J., Caraveo, P. A., Kerr, M., & Gonthier, P. L. Light-curve modelling constraints on the obliquities and aspect angles of the young Fermi pulsars. United States. doi:10.1051/0004-6361/201423815.
Pierbattista, M., Harding, A. K., Grenier, I. A., Johnson, T. J., Caraveo, P. A., Kerr, M., and Gonthier, P. L. Tue . "Light-curve modelling constraints on the obliquities and aspect angles of the young Fermi pulsars". United States. doi:10.1051/0004-6361/201423815. https://www.osti.gov/servlets/purl/1355164.
@article{osti_1355164,
title = {Light-curve modelling constraints on the obliquities and aspect angles of the young Fermi pulsars},
author = {Pierbattista, M. and Harding, A. K. and Grenier, I. A. and Johnson, T. J. and Caraveo, P. A. and Kerr, M. and Gonthier, P. L.},
abstractNote = {In more than four years of observation the Large Area Telescope on board the Fermi satellite has identified pulsed γ-ray emission from more than 80 young or middle-aged pulsars, in most cases providing light curves with high statistics. Fitting the observed profiles with geometrical models can provide estimates of the magnetic obliquity α and of the line of sight angle ζ, yielding estimates of the radiation beaming factor and radiated luminosity. Using different γ-ray emission geometries (Polar Cap, Slot Gap, Outer Gap, One Pole Caustic) and core plus cone geometries for the radio emission, we fit γ-ray light curves for 76 young or middle-aged pulsars and we jointly fit their γ-ray plus radio light curves when possible. We find that a joint radio plus γ-ray fit strategy is important to obtain (α,ζ) estimates that can explain simultaneously detectable radio and γ-ray emission: when the radio emission is available, the inclusion of the radio light curve in the fit leads to important changes in the (α,ζ) solutions. The most pronounced changes are observed for Outer Gap and One Pole Caustic models for which the γ-ray only fit leads to underestimated α or ζ when the solution is found to the left or to the right of the main α-ζ plane diagonal respectively. The intermediate-to-high altitude magnetosphere models, Slot Gap, Outer Gap, and One pole Caustic, are favoured in explaining the observations. We find no apparent evolution of α on a time scale of 106 years. For all emission geometries our derived γ-ray beaming factors are generally less than one and do not significantly evolve with the spin-down power. A more pronounced beaming factor vs. spin-down power correlation is observed for Slot Gap model and radio-quiet pulsars and for the Outer Gap model and radio-loud pulsars. The beaming factor distributions exhibit a large dispersion that is less pronounced for the Slot Gap case and that decreases from radio-quiet to radio-loud solutions. For all models, the correlation between γ-ray luminosity and spin-down power is consistent with a square root dependence. The γ-ray luminosities obtained by using the beaming factors estimated in the framework of each model do not exceed the spin-down power. This suggests that assuming a beaming factor of one for all objects, as done in other studies, likely overestimates the real values. The data show a relation between the pulsar spectral characteristics and the width of the accelerator gap. Furthermore, the relation obtained in the case of the Slot Gap model is consistent with the theoretical prediction.},
doi = {10.1051/0004-6361/201423815},
journal = {Astronomy and Astrophysics},
number = ,
volume = 575,
place = {United States},
year = {Tue Feb 10 00:00:00 EST 2015},
month = {Tue Feb 10 00:00:00 EST 2015}
}

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