A possible contribution of supernova remnants to the excess X-ray emission from the Galactic ridge

As a possible explanation for the thermal X-ray emission from the galactic ridge observed by the Tenma satellite, the authors examine the contribution of uncataloged supernova remnants (SNRs). Two constraints from the observations are imposed on the SNRs. One is that the temperature of the blast wave must be higher than ≡1 keV. The other is that the SNRs should fall below the detection limits of current radio surveys, since no radio SNRs are cataloged in the observed regions. The authors find that SNRs expanding in tenuous media (n < 0.1 cm^-3) satisfy these two conditions but still contribute significantly to the observed X-ray flux in the 2 - 11 keV band, if the supernova rate is approximately one per 10 yr.