Gravitational waves from newborn accreting millisecond magnetars

Two accretion columns have been argued to form over the surface of a newborn millisecond magnetar for an extremely high accretion rate greater than or similar to 1.8 x 10(-2) M-circle dot s(-1) that may occur in the core collapse of a massive star. In this paper, we investigate the characteristics of these accretion columns and their gravitational wave (GW) radiation. For a typical millisecond magnetar (surface magnetic field strength B similar to 10(15) G and initial spin period P similar to 1 ms), we find (i) its accretion columns are cooled via neutrinos and can reach a height similar to 1 km over the stellar surface; (ii) its column-induced characteristic GW strain is comparable to the sensitivities of the next-generation ground-based GW detectors within a horizon similar to 1 Mpc; (iii) the magnetar can survive only a few tens of seconds; (iv) during the survival timescale, the height of the accretion columns increases rapidly to the peak and subsequently decreases slowly; (v) the column mass, characteristic GW strain, and maximum GW luminosity have simultaneous peaks in a similar rise-fall evolution. In addition, we find that the magnetar's spin evolution is dominated by the column accretion torque. A possible association with failed supernova is also discussed.