X-Ray Emission from PSR B1800–21, Its Wind Nebula, and Similar Systems

We detected X-ray emission from PSR B1800-21 (J1803-2137) and its synchrotron nebula with the Chandra X-Ray Observatory. The observed pulsar flux is (1.4 ± 0.2) × 10^-14 ergs cm^-2 s^-1 in the 1-6 keV band. The spectrum can be described by a two-component power law + blackbody (PL + BB) model, suggesting a mixture of thermal and magnetospheric emission. For a plausible n_H = 1.4 × 10²² cm^-2, the PL component has a slope Γ = 1.4 ± 0.6 and a luminosity L = 4 × 10³¹(d/4 kpc)² ergs s^-1. The properties of the thermal component (kT = 0.1-0.3 keV, L = 10³¹-10³³ ergs s^-1) are very poorly constrained because of the strong interstellar absorption. The compact, 7'' × 4'', inner pulsar wind nebula (PWN), elongated perpendicular to the pulsar's proper motion, is immersed in a fainter asymmetric emission. The observed flux of the PWN is (5.5 ± 0.6) × 10^-14 ergs cm^-2 s^-1 in the 1-8 keV band. The PWN spectrum fits a PL model with Γ = 1.6 ± 0.3, L_PWN = 1.6 × 10³²(d/4 kpc)² ergs s^-1. The shape of the inner PWN suggests that the pulsar moves subsonically and X-ray emission emerges from a torus associated with the termination shock in the equatorial pulsar wind. The inferred PWN-pulsar properties (e.g., the PWN X-ray efficiency, L_PWN/Ė ~ 10^-4; the luminosity ratio, L_PWN/L = 4; the pulsar wind pressure at the termination shock, p_s = 10^-9 ergs cm^-3) are very similar to those of other subsonically moving Vela-like objects detected with Chandra (L_PWN/Ė ~ 10^-4.5 to 10^-3.5, L_PWN/L ~ 5, p_s = 10^-10 to 10^-8 ergs cm^-1).