Faculty Research at Morehead State University


Searching for the Pulsar in G18.95-1.1: Discovery of an X-ray Point Source and Associated Synchrotron Nebula with Chanda

Document Type


Publication Date



Using the Chandra X-ray Observatory, we have pinpointed the location of a faint X-ray point source (CXOU J182913.1–125113) and an associated diffuse nebula in the composite supernova remnant (SNR) G18.95–1.1. These objects appear to be the long-sought pulsar and its wind nebula. The X-ray spectrum of the point source is best described by an absorbed power-law model with Γ = 1.6 and an NH of ∼1 × 1022 cm−2. This model predicts a relatively low unabsorbed X-ray luminosity of about LX(0.5–8.0 keV) 4.1×1031 D2 2 erg s−1, where D2 is the distance in units of 2 kpc. The best-fit model of the diffuse nebula is a combination of thermal (kT = 0.48 keV) and non-thermal (1.4 Γ 1.9) emission. The unabsorbed X-ray luminosity of LX 5.4 × 1033 D2 2 erg s−1 in the 0.5–8 keV energy band seems to be largely dominated by the thermal component from the SNR, providing 87% of LX in this band. No radio or X-ray pulsations have been reported for CXOU J182913.1–125113. If we assume an age of ∼5300 yr for G18.95–1.1 and use the X-ray luminosity for the pulsar and the wind nebula together with the relationship between spin-down luminosity (via magnetic dipole radiation) and period, we estimate the pulsar’s period to be P 0.4 s. Compared to other rotation-powered pulsars, a magnetic field of 2.2×1013 G is implied by its location in the P–P˙ diagram, a value which is close to that of the quantum critical field.