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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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Cited by: 17works
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  • Here, we report the discovery of four gamma-ray pulsars, detected in computing-intensive blind searches of data from the Fermi Large Area Telescope (LAT). The pulsars were found using a novel search approach, combining volunteer distributed computing via Einstein@Home and methods originally developed in gravitational-wave astronomy. The pulsars PSRs J0554+3107, J1422–6138, J1522–5735, and J1932+1916 are young and energetic, with characteristic ages between 35 and 56 kyr and spin-down powers in the range 6 × 10 34—10 36 erg s –1. They are located in the Galactic plane and have rotation rates of less than 10 Hz, among which the 2.1 Hzmore » spin frequency of PSR J0554+3107 is the slowest of any known gamma-ray pulsar. For two of the new pulsars, we find supernova remnants coincident on the sky and discuss the plausibility of such associations. Deep radio follow-up observations found no pulsations, suggesting that all four pulsars are radio-quiet as viewed from Earth. These discoveries, the first gamma-ray pulsars found by volunteer computing, motivate continued blind pulsar searches of the many other unidentified LAT gamma-ray sources.« less
  • We report the discovery of four gamma-ray pulsars, detected in computing-intensive blind searches of data from the Fermi Large Area Telescope (LAT). The pulsars were found using a novel search approach, combining volunteer distributed computing via Einstein@Home and methods originally developed in gravitational-wave astronomy. The pulsars PSRs J0554+3107, J1422–6138, J1522–5735, and J1932+1916 are young and energetic, with characteristic ages between 35 and 56 kyr and spin-down powers in the range 6 × 10{sup 34}—10{sup 36} erg s{sup –1}. They are located in the Galactic plane and have rotation rates of less than 10 Hz, among which the 2.1 Hz spin frequency of PSR J0554+3107 ismore » the slowest of any known gamma-ray pulsar. For two of the new pulsars, we find supernova remnants coincident on the sky and discuss the plausibility of such associations. Deep radio follow-up observations found no pulsations, suggesting that all four pulsars are radio-quiet as viewed from Earth. These discoveries, the first gamma-ray pulsars found by volunteer computing, motivate continued blind pulsar searches of the many other unidentified LAT gamma-ray sources.« less
  • With the increasingly accepted notion that E-region electrostatic plasma waves move at their instability threshold speed when they attain their maximum amplitude, it has become more important to determine just what that threshold speed is supposed to be. An accurate determination requires a calculation of the electron temperature fluctuation level, which can sometimes dramatically influence the results. In this paper, the Grad 8-moment transport equations have been employed with the addition of a generalized electron cooling rate to account for cooling via inelastic collisions, and a general electron volume heating rate that includes frictional heating as a special case. Themore » derived generalized dispersion relation is presented in such a way that a variety of other earlier treatments, including the isothermal and adiabatic limits and an instability associated with electron friction, all fall out transparently, allowing us to easily compare our results with earlier ones while tracking down the physical processes involved. The presentation format is also geared to facilitate the computation of the dispersion relation for the purpose of comparing the theoretical results with observations.« less
  • Here, we report on the results of a recent blind search survey for gamma-ray pulsars in Fermi Large Area Telescope (LAT) data being carried out on the distributed volunteer computing system, Einstein@Home. The survey has searched for pulsations in 118 unidentified pulsar-like sources, requiring about 10,000 years of CPU core time. In total, this survey has resulted in the discovery of 17 new gamma-ray pulsars, of which 13 are newly reported in this work, and an accompanying paper. These pulsars are all young, isolated pulsars with characteristic ages between 12 kyr and 2 Myr, and spin-down powers between 10 34 and 4 × 10 36 erg s -1. Two of these are the slowest spinning gamma-ray pulsars yet known. One pulsar experienced a very large glitchmore » $${\rm{\Delta }}f/f\approx 3.5\times {10}^{-6}$$ during the Fermi mission. In this, the first of two associated papers, we describe the search scheme used in this survey, and estimate the sensitivity of our search to pulsations in unidentified Fermi-LAT sources. One such estimate results in an upper limit of 57% for the fraction of pulsed emission from the gamma-ray source associated with the Cas A supernova remnant, constraining the pulsed gamma-ray photon flux that can be produced by the neutron star at its center. Lastly, we also present the results of precise timing analyses for each of the newly detected pulsars.« less
  • Context. Since the launch of the Fermi satellite, the number of known gamma-ray pulsars has increased tenfold. Most gamma-ray detected pulsars are young and energetic, and many are associated with TeV sources. PSR J1357-6429 is a high spin-down power pulsar (È = 3.1 × 1036 erg s -1), discovered during the Parkes multibeam survey of the Galactic plane, with significant timing noise typical of very young pulsars. In the very-high-energy domain (E > 100 GeV), H.E.S.S. has reported the detection of the extended source HESS J1356-645 (intrinsic Gaussian width of 12') whose centroid lies 7' from PSR J1357-6429. Aims. Wemore » search for gamma- and X-ray pulsations from this pulsar, characterize the neutron star emission and explore the environment of PSR J1357-6429. Methods. Using a rotational ephemeris obtained with 74 observations made with the Parkes telescope at 1.4 GHz, we phase-fold more than two years of gamma-ray data acquired by the Large Area Telescope on-board Fermi as well as those collected with XMM-Newton, and perform gamma-ray spectral modeling. Results. Significant gamma- and X-ray pulsations are detected from PSR J1357-6429. The light curve in both bands shows one broad peak. Gamma-ray spectral analysis of the pulsed emission suggests that it is well described by a simple power-law of index 1.5 ± 0.3 stat ± 0.3 syst with an exponential cut-off at 0.8 ± 0.3 stat ± 0.3 syst GeV and an integral photon flux above 100 MeV of (6.5 ± 1.6 stat ± 2.3 syst) × 10 -8 cm -2 s -1. The X-ray spectra obtained from the new data provide results consistent with previous work. Upper limits on the gamma-ray emission from its potential pulsar wind nebula (PWN) are also reported. Conclusions. Assuming a distance of 2.4 kpc, the Fermi LAT energy flux yields a gamma-ray luminosity for PSR J1357-6429 of L γ = (2.13 ± 0.25 stat ± 0.83 syst) × 1034 erg s -1, consistent with an relationship. The Fermi non-detection of the pulsar wind nebula associated with HESS J1356-645 provides new constraints on the electron population responsible for the extended TeV emission.« less