Diffuse Hard X‐Ray Sources Discovered with theASCAGalactic Plane Survey

We found diffuse hard X-ray sources, G11.0+0.0, G25.5+0.0, and G26.6-0.1 inthe ASCA Galactic plane survey data. The X-ray spectra are featureless with noemission line, and are fitted with both models of a thin thermal plasma innon-equilibrium ionization and a power-law function. The source distances areestimated to be 1-8 kpc, using the best-fit NH values on the assumption thatthe mean density in the line of sight is 1 H cm^-3. The source sizes andluminosities are then 4.5-27 pc and (0.8-23)x10^33 ergs/s. Although the sourcesizes are typical to supernova remnants (SNR) with young to intermediate ages,the X-ray luminosity, plasma temperature, and weak emission lines in thespectra are all unusual. This suggests that these objects are either shell-likeSNRs dominated by X-ray synchrotron emission, like SN 1006, or, alternatively,plerionic SNRs. The total number of these classes of SNRs in our Galaxy is alsoestimated.Comment: 17 pages, 9 figures; to appear in Ap