Chandra Observation of PSR B1823–13 and Its Pulsar Wind Nebula

An observation of the Vela-like pulsar B1823–13 and its synchrotron nebula with the Chandra X-Ray Observatory allowed us to resolve the pulsar and the fine structure of the nebula. The pulsar's spectrum fits a power-law model with a photon index Γ_PSR ≈ 2.4 for the plausible hydrogen column density n_H = 1 × 10²² cm⁻², corresponding to the luminosity L_PSR ≈ 8 × 10³¹ ergs s⁻¹ in the 0.5-8 keV band, at a distance of 4 kpc. The pulsar radiation likely includes magnetospheric and thermal components, but they cannot be reliably separated, because of the small number of counts detected and strong interstellar absorption. The pulsar is surrounded by a compact, ~25'' × 10'', pulsar wind nebula (PWN) elongated in the east-west direction, which includes a brighter inner component ≈7'' × 3'', elongated in the northeast-southwest direction. The slope of the compact PWN spectrum is Γ_comp ≈ 1.3, and the 0.5-8 keV luminosity is L_comp ∼ 3 × 10³² ergs s⁻¹. The compact PWN is surrounded by asymmetric diffuse emission (extended PWN) seen up to at least 2.4' south of the pulsar, with a softer spectrum (Γ_ext ≈ 1.9 for n_H = 1 × 10²² cm⁻²), and the 0.5-8 keV luminosity L_ext ∼ 10³³-10³⁴ ergs s⁻¹. We also measured the pulsar's proper motion using archival VLA data, μ_α = 23.0 ± 2.5 mas yr⁻¹ and μ_δ = − 3.9 ± 3.1 mas yr⁻¹ (in LSR), which corresponds to the transverse velocity v_⊥ ≈ 440 km s⁻¹. The direction of the proper motion is approximately parallel to the elongation of the compact PWN, but it is nearly perpendicular to that of the extended PWN and to the direction toward the center of the bright VHE γ-ray source HESS J1825–137, which is believed to be powered by PSR B1823–13.