PSR J1838-0655: X-Ray Observations with NICER and NuSTAR

Abstract: We report on the timing and spectral properties of PSR J1838-0655 using joint observations from the Neutron Star Interior Composition Explorer (NICER) and the Nuclear Spectroscopic Telescope Array (NuSTAR). By disentangling the pulsar's emission from its surrounding wind nebula across joint Chandra, NuSTAR, and NICER observations, we find the pulsar's broad-band X-ray spectrum (1.3--79\,keV) is best-described by a broken power-law model. The model features photon indices of $\Gamma_1 = 1.19 \pm 0.07$ and $\Gamma_2 = 1.47 \pm 0.02$ below and above a break energy of $E_{\rm b} = 7.7 \pm 0.8$\,keV. The resulting unabsorbed 2--10\,keV flux from the pulsar is $(9.5^{+0.4}_{-0.3}) \times 10^{-12}~\mathrm{erg\,cm^{-2}\,s^{-1}}$. Furthermore, timing analysis of NICER data spanning MJD 58250 to 60630 reveals a very large glitch occurring around MJD 59300, characterized by a frequency jump of $\Delta \nu = 29.367(7) \times 10^{-6}$ Hz, which can be well explained by the vortex creep model. Phase-resolved spectral analysis indicates a clear anti-correlation between the photon index and the pulse intensity, suggesting spectral hardening at the pulse peak.