X-ray studies of PSR J1838$-$0655 and its wind nebula associated with HESS J1837$-$069 and 1LHAASO J1837$-$0654u

Abstract

We analyzed X-ray data from Chandra, XMM-Newton, NICER, and NuSTAR to characterize the properties of the pulsar PSR J1838$-$0655 and its pulsar wind nebula (PWN) associated with HESS J1837$-$069. Based on 5.5 years of NICER monitoring, we detected a glitch around MJD 59300, characterized by a fractional frequency jump of approximately $2\times 10^{-6}$. We constructed semi-phase-coherent timing solutions for pre- and post-glitch epochs, allowing for phase alignment of multi-instrument data and a subsequent measurement of the pulsed spectrum of the pulsar. This analysis confirmed previously-reported spectral curvature and revealed a peak energy of $73^{+85}_{-26}$ keV in the pulsar's spectral energy distribution (SED), based on a logpar model fit of the pulsed spectrum. We discuss these findings within the framework of pulsar magnetospheric emission scenarios. The PWN's X-ray spectrum is well-described by a power law with a photon index of $2.1\pm0.3$, softer than previously-reported measurements. We also characterized the X-ray emission from another extended X-ray source AX J1837.3$-$0652 within the extent of HESS J1837$-$069. Based on the spatial and spectral properties of these X-ray sources, we propose a leptonic emission scenario for HESS J1837$-$069 and demonstrate its feasibility through SED modeling. Finally, we discuss the implications of our model results and alternative scenarios for the gamma-ray emission.