We report on our serendipitous pre-discovery detection and detailed follow-up of the broad-lined Type Ic supernova ( SN ) 2010ay at z = 0.067 imaged by the Pan-STARRS1 3 \pi survey just \sim 4 { } days after explosion .
The SN had a peak luminosity , M _ { R } \approx - 20.2 mag , significantly more luminous than known GRB-SNe and one of the most luminous SNe Ib/c ever discovered .
The absorption velocity of SN 2010ay is v _ { Si } \approx 19 \times 10 ^ { 3 } ~ { } km s ^ { -1 } at \sim 40 days after explosion , 2 - 5 times higher than other broad-lined SNe and similar to the GRB-SN 2010bh at comparable epochs .
Moreover , the velocity declines \sim 2 times slower than other SNe Ic-BL and GRB-SNe .
Assuming that the optical emission is powered by radioactive decay , the peak magnitude implies the synthesis of an unusually large mass of ^ { 56 } Ni , M _ { Ni } = 0.9 ~ { } M _ { \odot } .
Modeling of the light-curve points to a total ejecta mass , M _ { ej } \approx 4.7 { } M _ { \odot } , and total kinetic energy , E _ { K } \approx 11 \times 10 ^ { 51 } ergs .
The ratio of M _ { Ni } to M _ { ej } is \sim 2 times as large for SN 2010ay as typical GRB-SNe and may suggest an additional energy reservoir .
The metallicity ( \log ( { O / H } ) _ { PP 04 } +12 = 8.19 { } ) of the explosion site within the host galaxy places SN 2010ay in the low-metallicity regime populated by GRB-SNe , and \sim 0.5 ( 0.2 ) dex lower than that typically measured for the host environments of normal ( broad-lined ) Ic supernovae .
We constrain any gamma-ray emission with E _ { \gamma } \lesssim 6 \times 10 ^ { 48 } erg ( 25-150 keV ) and our deep radio follow-up observations with the Expanded Very Large Array rule out relativistic ejecta with energy , E \gtrsim 10 ^ { 48 } erg .
We therefore rule out the association of a relativistic outflow like those which accompanied SN 1998bw and traditional long-duration GRBs , but place less-stringent constraints on a weak afterglow like that seen from XRF 060218 .
These observations challenge the importance of progenitor metallicity for the production of a GRB , and suggest that other parameters also play a key role .