Constraining millisecond pulsar geometry using time-aligned radio and gamma-ray pulse profile
Résumé
Context. Since the launch of the Fermi Gamma-Ray Space Telescope, several hundred gamma-ray pulsars have been discovered, some being radio-loud and some radio-quiet with time-aligned radio and gamma-ray light curves. In the second Fermi Pulsar Catalogue, 117 new gamma-ray pulsars have been reported based on three years of data collected by the Large Area Telescope on the Fermi satellite, providing a wealth of information such as the peak separation Δ of the gamma-ray pulsations and the radio lag δ between the gamma-ray and radio pulses.
Aim: We selected several radio-loud millisecond gamma-ray pulsars with period P in the range 2–6 ms and showing a double peak in their gamma-ray profiles. We attempted to constrain the geometry of their magnetosphere, namely the magnetic axis and line-of-sight inclination angles for each of these systems.
Method: We applied a force-free dipole magnetosphere from the stellar surface up to the striped wind region – well outside the light cylinder – to fit the observed pulse profiles in gamma-rays, consistently with their phase alignment with the radio profile. In deciding whether a fitted curve is reasonable or not, we employed a least-square method to compare the observed gamma-ray intensity with that found from our model, emphasising the amplitude of the gamma-ray peaks, their separation, and the phase lag between radio and gamma-ray peaks.
Results: We obtained the best fits and reasonable parameters in agreement with observations for ten millisecond pulsars. Eventually, we constrained the geometry of each pulsar described by the magnetic inclination α and the light-of-sight inclination ζ. We found that both angles are larger than approximately 45°.
Origine : Publication financée par une institution