A Search For Supernova Remnants in The Nearby Spiral Galaxy M74 (NGC
  628)
  We have identified nine new SNR candidates in M74 with [S II]/H$\alpha$
$\geq$ 0.4 as the basic criterion. We obtain [S II]/H$\alpha$ ratio in the
range from 0.40 to 0.91 and H$\alpha$ intensities from 2.8 $\times$ $10^{-15}$
erg cm$^{-2}$ s$^{-1}$ to 1.7 $\times$ $10^{-14}$ erg cm$^{-2}$ s$^{-1}$. We
also present spectral follow-up observations of the SNR candidates and can
confirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for
the rest might be due to the contamination by the nearby H II emission regions
as well as due to the inaccurate positioning of the long slit on these objects.
In addition, we search the $Chandra$ Observatory archival data for the X-ray
counterparts to the optically identified candidates. We find positional
coincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum
of SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of
1.6 $\times$ 10$^{10}$ s cm$^{-3}$ indicating a relatively young remnant in an
early Sedov phase which is not supported by our optical wavelength analysis.
Given the high luminosity of 10$^{39}$ erg s$^{-1}$ and the characteristics of
the X-ray spectrum, we favor an Ultra Luminous X-ray Source interpretation for
this source associated with an SNR. We calculate an X-ray flux upper limit of
9.0 $\times$ $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ for the rest of the SNRs
including spectroscopically identified SNR3 and SNR5.
