We discuss a scenario of short Gamma-Ray Bursts ( GRBs ) following a merger of a massive ONeMg white dwarf ( WD ) with a CO WD , and an ensuing accretion induced collapse ( AIC ) .
An initial system with the primary mass M _ { 1 } \sim 6 - 10 M _ { \odot } and the secondary mass M _ { 2 } \sim 3 - 6 M _ { \odot } forms , via two distinct evolutionary channels , a double degenerate CO-ONeMg WD system .
For sufficiently large mass ratio q \equiv M _ { 2 } / M _ { 1 } > q _ { crit } \sim 0.25 the ensuing gravitational wave-driven mass transfer is unstable , whereby the less massive CO WD is disrupted and transfers its mass to the primary ONeMg WD on a few orbital time scales .
The merger product ignites shell CO burning , adding mass to the degenerate core ; at the same time mass and angular momentum is lost due to powerful winds .
For an ONeMg WD sufficiently close to the Chandrasekhar mass an electron-capture accretion induced collapse ( AIC ) follows \sim 10 ^ { 4 } years afterwards .
We associate the prompt short GRB emission with a direct collapse of an ONeMg WD to a neutron star , without formation of an accretion disk .
After the collapse the accretion of the unburnt part of the shell onto the newly formed NS powers the extended emission ( EE ) .
During the collapse the neutron star is spun to millisecond periods and produce long lasting relativistic winds that shock against the material lost during the shell-burning stage , and produce afterglow emission from the wind termination shock .