Constraints on Emission Models by Broadband Observations of Soft Gamma-Ray Pulsar PSR B1509–58

Abstract Soft γ -ray pulsars featuring broad single peaks exhibit different observational properties compared to ordinary double-peaked high-energy pulsars. These two types of pulsars are considered to be the result of different viewing angles. Therefore, the radiation characteristics of soft γ -ray pulsars play a crucial role in testing radiation models. However, the weak fluxes of the broad single-peak pulsars in the high-energy range have limited in-depth research on them in the past. In this work, the profile and spectral analysis of PSR B1509–58 from keV to GeV energies are performed using new observations from NICER, Insight-HXMT, and Fermi GBM-NaI/LAT. We find that the pulse profile narrows as the energy increases, and the FWHM can be fitted with FWHM = (0.35 ± 0.02) · ( E /1 keV) −0.053 ± 0.009 . The phase-averaged spectrum fitted by a modified super exponential cutoff power law model reveals that the energy corresponding to the maximum luminosity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> is 2.1 ± 1 MeV. Furthermore, we fit the pulse profiles across different energy bands using a geometric annular gap model. Within the framework of this model, the observed narrowing of the pulse profile and the rapid softening of the phase-averaged spectrum can be interpreted as a result of the radiation angle moving away from the magnetic axis with increasing energy. The observational and modeling results support the existence of an annular gap acceleration region located inside the null-charge surface, suggesting that higher-energy radiation originates from areas closer to the surface of the neutron star.