The supernova remnant population of the Small Magellanic Cloud
  Aims: We present a comprehensive study of the supernova remnant (SNR)
population of the Small Magellanic Cloud (SMC). We measure multiwavelength
properties of the SMC SNRs and compare them to those of the Large Magellanic
Cloud (LMC) population. Methods: This study combines the large dataset of
XMM-Newton observations of the SMC, archival and recent radio continuum
observations, an optical line emission survey, and new optical spectroscopic
observations. We can thus build a complete and clean sample of 19 confirmed and
4 candidate SNRs. The homogeneous X-ray spectral analysis allows to search for
SN ejecta and Fe K line emission, and to measure interstellar medium (ISM)
abundances. We estimate the ratio of core-collapse to type Ia supernova rates
of the SMC based on the X-ray properties and the local stellar environment of
each SNR. Results : After the removal of unconfirmed or misclassified objects,
and the addition of two newly confirmed SNRs based on multi-wavelength
features, we present a final list of 21 confirmed SNRs and 2 candidates. While
no Fe K line is detected even for the brightest and youngest SNR, we find X-ray
evidence of SN ejecta in 11 SNRs. We estimate a ratio of 4.7$_{-1.9} ^{+0.6}$
core-collapse supernova to every type Ia SN, three times higher than in the
LMC. The difference can be ascribed to the absence of the enhanced star
formation episode in the SMC, which occurred in the LMC 0.5-1.5 Gyr ago. The
hot-gas abundances of O, Ne, Mg, and Fe are 0.1-0.2 times solar. Their ratios
with respect to SMC stellar abundances reflect the effects of dust depletion
and partial dust destruction in SNR shocks. We find evidence that the ambient
medium probed by SMC SNRs is less disturbed and less dense on average than in
the LMC, consistent with the different morphologies of the two galaxies.
