ChandraObservation of PSR B1823−13 and Its Pulsar Wind Nebula

Abstract

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 ΓPSR ≈ 2.4 for the plausible hydrogen column density nH = 1 × 1022 cm−2, corresponding to the luminosity LPSR ≈ 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 Γcomp ≈ 1.3, and the 0.5-8 keV luminosity is Lcomp ~ 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 (Γext ≈ 1.9 for nH = 1 × 1022 cm−2), and the 0.5-8 keV luminosity Lext ~ 1033-1034 ergs s−1. We also measured the pulsar's proper motion using archival VLA data, μα = 23.0 ± 2.5 mas yr−1 and μδ = − 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.