Emission mechanism of GeV-quiet soft gamma-ray pulsars; A case for peculiar geometry?

Abstract

There is a growing new class of young spin-down powered pulsars called GeV-quiet soft gamma-ray pulsar; (1) spectral turnover appears around~10MeV, (2) the X-ray spectra of below 20 keV can be described by power law with photon index around 1.2 and (3) the light curve in X-ray/soft gamma-ray bands shows single broad pulse. Their emission properties are distinct from the normal gamma-ray pulsars, for which the spectral peak in $\nu F_{\nu }$ appears in GeV energy bands and the X-ray/gamma-ray light curves show sharp and double (or more) peaks. In this paper, we discuss that X-ray/soft gamma-ray emissions of the GeV-quiet soft gamma-ray pulsars are caused bythe synchrotron radiation of the electron/positron pairs, which are created by the magnetic pair-creation process near the stellar surface. In our model, the viewing geometry is crucial factor to discriminate between the normal gamma-ray pulsars and soft gamma-ray pulsars. Our model suggests that the difference between the magnetic inclination angle ($\alpha$) and the Earth viewing angle ($\beta$) of the soft gamma-ray pulsars is small, so that the synchrotron emissions from the high magnetic field region around the polar cap region dominates in the observed emissions. Furthermore, the inclination angle of the soft gamma-ray pulsar is relatively small, $\alpha \le 30$~degree, and our line of sight is out of the gamma-ray beam emitted via the curvature radiation process in the outer gap. We also analysis the six year $Fermi$ data for four soft gamma-ray pulsars to determine the upper limit of the GeV flux.

21pages, 8 figures. Accepted by MNRAS

References in corpus (14)

• The ATNF Pulsar Catalogue
• The 3rd IBIS/ISGRI soft gamma-ray survey catalog
• Magnetar-like Emission from the Young Pulsar in Kes 75
• Observation of Pulsed Gamma-rays Above 25 GeV from the Crab Pulsar with MAGIC
• Fitting Pulsar Wind Tori. II. Error Analysis and Applications
• The Distance of the SNR Kes 75 and PWN PSR J1846-0258 System
• Particle Accelerator in Pulsar Magnetospheres: Super Goldreich-Julian Current with Ion Emission from the Neutron Star Surface
• Deep Chandra Observation of the Pulsar Wind Nebula Powered by the Pulsar J1846-0258 in the Supernova Remnant Kes 75
• Particle Acceleration and Non-Thermal Emission in Pulsar Outer Magnetospheric Gap
• No detectable radio emission from the magnetar-like pulsar in Kes 75
• HESS J1616-508: likely powered by PSR J1617-5055
• INTEGRAL detection of the pulsar wind nebula in PSR J1846-0258
• INTEGRAL observations of PSR J1811-1925 and its associated Pulsar Wind Nebula
• X-ray Timing Observations of PSR J1930+1852 in the Crab-like SNR G54.1+0.3

Cited by in corpus (3)

• The Fermi LAT detection of magnetar-like pulsar PSR J1846-0258 at high-energy gamma-rays
• Precise timing and phase-resolved spectroscopy of the young pulsar J1617-5055 with NuSTAR
• Investigating the neutron star physics through observations of several young pulsars in the dipole-field re-emergence scenario