We present optical observations of type Ia supernova ( SN ) 2019ein , starting at 2 days after the estimated explosion date .
The spectra and the light curves show that SN 2019ein belongs to the High-Velocity ( HV ) and Bload Line groups with relatively rapid decline in the light curves ( \Delta m _ { 15 } ( B ) = 1.36 \pm 0.02 mag ) and the short rise time ( 15.37 \pm 0.55 days ) .
The Si ii \lambda 6355 velocity , associated with a photospheric component but not with a detached high-velocity feature , reached \sim 20,000 km s ^ { -1 } at 12 days before the B -band maximum .
The line velocity however decreased very rapidly and smoothly toward the maximum light , where it was \sim 13 , 000 km s ^ { -1 } as relatively low among HV SNe .
This indicates that the speed of the spectral evolution of HV SNe Ia is correlated not only to the velocity at the maximum light , but also to the light curve decline rate like the case for Normal-Velocity ( NV ) SNe Ia .
Spectral synthesis modeling shows that the outermost layer at > 17 , 000 km s ^ { -1 } is well described by the O-Ne-C burning layer extending to at least 25 , 000 km s ^ { -1 } , and there is no unburnt carbon below 30 , 000 km s ^ { -1 } ; these properties are largely consistent with the delayed detonation scenario , and are shared with the prototypical HV SN 2002bo despite the large difference in \Delta m _ { 15 } ( B ) .
This structure is strikingly different from that derived for the well-studied NV SN 2011fe .
We suggest that the relation between the mass of ^ { 56 } Ni ( or \Delta m _ { 15 } ) and the extent of the O-Ne-C burning layer provides an important constraint on the explosion mechanism ( s ) of HV and NV SNe .