  New narrow-band HAlpha imaging and subsequent optical spectra confirm
G315.1+2.7, a previously identified candidate supernova remnant (SNR), as a
bona-fide Galactic SNR. Present observations are based on independent discovery
of filamentary optical emission nebulosity on images of the AAO/UKST HAlpha
survey of the southern Galactic plane which were found to co-incide with
existing multi-frequency radio detections. Separate medium and high dispersion
spectra were taken across two locations of this 11 arcmin N-S aligned optical
filament. The resulting spectral signatures were found to strongly confirm the
SNR identification based on standard emission line ratio discriminators which
characterise emission from shock heated gas. The average observed ratios of
[SII]/HAlpha=1.13, [NII]/HAlpha=1.43 and [SII] 6717/6731=1.46, together with
the simultaneous detection of [OII] at 3727A, [OIII] 5007A and [OI] 6300A, all
point to an SNR origin of the observed optical emission. Careful scrutiny of
the low-resolution but high sensitivity SHASSA HAlpha survey also revealed a
low-level but distinct optical emission arc. This arc precisely correlates with
the large, 2.5 degree, north-south angular extent of the proposed new SNR also
seen as a fractured structure in the extant radio data. G315.1+2.7 was detected
previously at 2400 and 4800 MHz and at 408 and 1420 MHz. We also identified
associated radio emission at 843 MHz from the now publicly available SUMSS
survey. On the basis of optical imaging and spectra and radio observations at
five frequencies, we identify G315.1+2.7 as a new Galactic SNR. The large
projected angular extent of the new remnant, together with the distance
estimate of ~1.7 kpc and diameter of ~80pc, make G315.1+2.7 one of the largest
remnants known.
