We present multi-band photometric and optical spectroscopic observations of SN2007ax , the faintest and reddest Type Ia supernova ( SN Ia ) yet observed .
With M _ { B } = - 15.9 and ( B - V ) _ { max } = 1.2 , this SN is over half a magnitude fainter at maximum light than any other SN Ia .
Similar to subluminous SN2005ke , SN2007ax also appears to show excess in UV emission at late time .
Traditionally , \Delta m _ { 15 } ( B ) has been used to parameterize the decline rate for SNe Ia .
However , the B-band transition from fast to slow decline occurs sooner than 15 days for faint SNe Ia .
Therefore we suggest that a more physically motivated parameter , the time of intersection of the two slopes , be used instead .
Only by explaining the faintest ( and the brightest ) supernovae , we can thoroughly understand the physics of thermonuclear explosions .
We suggest that future surveys should carefully design their cadence , depth , pointings and follow-up to find an unbiased sample of extremely faint members of this subclass of faint SNe Ia .