Neutron-star ( NS ) - white-dwarf ( WD ) mergers may give rise to observable explosive transients , but have been little explored .
We use 2D coupled hydrodynamical-thermonuclear FLASH-code simulations to study the evolution of WD debris-disks formed following WD-disruptions by NSs .
We use a 19-elements nuclear-network and a detailed equation-of-state to follow the evolution , complemented by a post-process analysis using a larger 125-isotopes nuclear-network .
We consider a wide range of initial conditions and study the dependence of the results on the NS/WD masses ( 1.4 - 2 { M _ { \odot } } ; { 0.375 - 0.7 M _ { \odot } } , respectively ) , WD-composition ( CO/He/hybrid-He-CO ) and the accretion-disk structure .
We find that viscous inflow in the disk gives rise to continuous wind-outflow of mostly C/O material mixed with nuclear-burning products arising from a weak detonation occurring in the inner-region of the disk .
We find that such transients are energetically weak ( 10 ^ { 48 } -10 ^ { 49 } ergs ) compared with thermonuclear-supernovae ( SNe ) , and are dominated by the ( gravitational ) accretion-energy .
Although thermonuclear-detonations occur robustly in all of our simulations ( besides the He-WD ) they produce only little energy ( 1 - 10 \% of the kinetic energy ) and ^ { 56 } { Ni } ejecta ( few \times 10 ^ { -4 } -10 ^ { -3 } { M _ { \odot } } ) , with overall low ejecta masses of \sim 0.01 - 0.1 { M _ { \odot } } .
Such explosions may produce rapidly-evolving transients , much shorter and fainter than regular type-Ia SNe .
The composition and demographics of such SNe appear to be inconsistent with those of Ca-rich type Ib SNe .
Though they might be related to the various classes of rapidly evolving SNe observed in recent years , they are likely to be fainter than the typical ones , and may therefore give rise a different class of potentially observable transients .