NGC 5471B has been suggested to contain a hypernova remnant because of its extraordinarily bright X-ray emission .
To assess its true nature , we have obtained high-resolution images in continuum bands and nebular lines with the Hubble Space Telescope , and high-dispersion long-slit spectra with the Kitt Peak National Observatory 4-m echelle spectrograph .
The images reveal three supernova remnant ( SNR ) candidates in the giant H ii region NGC 5471 , with the brightest one being the 77 \times 60 pc shell in NGC 5471B .
The H \alpha velocity profile of NGC 5471B can be decomposed into a narrow component ( FWHM = 41 km s ^ { -1 } ) from the background H ii region and a broad component ( FWHM = 148 km s ^ { -1 } ) from the SNR shell .
Using the brightness ratio of the broad to narrow components and the H \alpha flux measured from the WFPC2 H \alpha image , we derive an H \alpha luminosity of ( 1.4 \pm 0.1 ) \times 10 ^ { 39 } ergs s ^ { -1 } for the SNR shell .
The [ S ii ] \lambda 6716/ \lambda 6731 doublet ratio of the broad velocity component is used to derive an electron density of \sim 700 cm ^ { -3 } in the SNR shell .
The mass of the SNR shell is thus 4600 \pm 500 M _ { \odot } .
With a \sim 330 km s ^ { -1 } expansion velocity implied by the extreme velocity extent of the broad component , the kinetic energy of the SNR shell is determined to be 5 \times 10 ^ { 51 } ergs .
This requires an explosion energy greater than 10 ^ { 52 } ergs , which can be provided by one hypernova or multiple supernovae .
Comparing to SNRs in nearby active star formation regions , the SNR shell in NGC 5471B appears truly unique and energetic .
We conclude that the optical observations support the existence of a hypernova remnant in NGC 5471B .