X-ray observations of supernova remnant G54.1+0.3: X-ray spectrum and the discovery of an X-ray jet

We present in this paper analyses of the $ROSAT$ PSPC and $ASCA$ SIS and GIS observations of the Crab-like supernova remnant (SNR) G54.1+0.3. Its spectrum obtained by $ROSAT$ PSPC favors a power law model with a photon index of -0.8${}_{-2.0}^{+0.8}$, absorbed energy flux in 0.1-2.4 keV of 1.0$\times 10^{-12}$ergcm$^{-2}$s$^{-1}$, and absorption column density of 12.3${}_{-3.2}^{+8.0}\times {10}^{21}$ cm${}^{-2}$. $ASCA$ SIS observation shows that its spectrum can also be best fitted with power law model. The fitted parameters are, photon index -1.9${}_{-0.2}^{+0.1}$, absorbed energy flux in 0.7-2.1 keV 6.5$\times {10}^{-13}$ erg cm${}^{-2}$ s${}^{-1}$, and column density 17.9${}_{-2.5}^{+2.8}\times {10}^{21}$ cm${}^{-2}$. The high absorption column density indicates a distance similar to the radius of the galaxy. The 0.1-2.4 keV X-ray luminosity of G54.1+0.3 is 3.2$\times {10}^{33}$$d_{10}^2$ erg s${}^{-1}$, where $d_{10}$ is the distance in 10 kpc. With an image restoration method we have obtained high spatial resolution X-ray image of the remnant, which clearly shows an X-ray jet pointing to the northeast with a length about 40$\text{arcsec}$ from the center of the nebula. Its X-ray luminosity in 0.1-2.4 keV is about 5.1$\times {10}^{32}$$d_{10}^2$ erg s${}^{-1}$. The X-ray jet is consistent with the radio extension to the northeast in both direction and position. We propose that the X-ray jet is connected with the pulsar assumed to exist in the remnant.