TY - JOUR

T1 - An assessment of the pulsar outer gap model - II. Implications for the predicted γ-ray spectra

AU - Viganò, Daniele

AU - Torres, Diego F.

AU - Hirotani, Kouichi

AU - Pessah, Martín E.

PY - 2015/1/1

Y1 - 2015/1/1

N2 - © 2015 The Authors. One of the most important predictions of any gap model for pulsar magnetospheres is the predicted γ-ray spectra. In the outer gap model, the properties of the synchro-curvature radiation are sensitive to many parameters, whose realistic ranges have been studied in detail in an accompanying paper. There we demonstrated that the uncertainty in the radius of curvature, the magnetic field geometry, and the X-ray surface flux may affect by orders of magnitude the predicted flux and spectral peak in the γ-ray regime. Here, we present a systematic, numerical study of the impact of the different parameters on the particle dynamics along the gap and calculate the emitted synchro-curvature radiation along the trajectory. By integrating the emitted radiation along the gap and convolving it with a parametrized particle distribution, we discuss how the comparison with the wealth of Fermi-LAT data can be used to constrain the applicability of the model. The resulting spectra show very different energy peaks, fluxes, and shapes, qualitatively matching the great variety of the observed Fermi-LAT pulsars. In particular, if we see a large fraction of photons emitted from the initial part of the trajectory, we show that the spectra will be flatter at the low-energy Fermi-LAT regime (100 MeV-1 GeV). This provides a solution for such observed flat spectra, while still maintain synchro-curvature radiation as the origin of these photons.

AB - © 2015 The Authors. One of the most important predictions of any gap model for pulsar magnetospheres is the predicted γ-ray spectra. In the outer gap model, the properties of the synchro-curvature radiation are sensitive to many parameters, whose realistic ranges have been studied in detail in an accompanying paper. There we demonstrated that the uncertainty in the radius of curvature, the magnetic field geometry, and the X-ray surface flux may affect by orders of magnitude the predicted flux and spectral peak in the γ-ray regime. Here, we present a systematic, numerical study of the impact of the different parameters on the particle dynamics along the gap and calculate the emitted synchro-curvature radiation along the trajectory. By integrating the emitted radiation along the gap and convolving it with a parametrized particle distribution, we discuss how the comparison with the wealth of Fermi-LAT data can be used to constrain the applicability of the model. The resulting spectra show very different energy peaks, fluxes, and shapes, qualitatively matching the great variety of the observed Fermi-LAT pulsars. In particular, if we see a large fraction of photons emitted from the initial part of the trajectory, we show that the spectra will be flatter at the low-energy Fermi-LAT regime (100 MeV-1 GeV). This provides a solution for such observed flat spectra, while still maintain synchro-curvature radiation as the origin of these photons.

KW - Gamma-rays: stars

KW - Pulsars: general

KW - Stars: neutron

U2 - 10.1093/mnras/stu2565

DO - 10.1093/mnras/stu2565

M3 - Article

VL - 447

SP - 2649

EP - 2657

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 3

ER -