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$^{+0.8}_{-2.0}$, absorbed energy flux in 0.1-2.4 keV of 1.0$\times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$, and absorption column density of 12.3$^{+8.0}_{-3.2}\times 10^{21}$ 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$^{+0.1}_{-0.2}$, absorbed energy flux in 0.7-2.1 keV 6.5$\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$, and column density 17.9$^{+2.8}_{-2.5}\times 10^{21}$ 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$\times10^{33}$$d_{10}^2$ erg s$^{-1}$, where $d_{10}$ is the distance in 10 kpc. With an image restoration method we have obtained high spatial resolution X-ray image of the remnant, which clearly shows an X-ray jet pointing to the northeast with a length about 40$\arcsec$ from the center of the nebula. Its X-ray luminosity in 0.1-2.4 keV is about 5.1$\times10^{32}$$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. 
F.J. Lu (1,2), B. Aschenbach (1), L.M. Song (2)   ((1)Max-Planck-Institut fur Extraterrestrische Physik (2)Institute of High...