  The crucial observation on the occurrence of subpulses (overtones) in the
Power Spectral Density of the August 27 (1998) event from SGR1900+14, as
discovered by BeppoSAX (Feroci et al. 1999), has received no consistent
explanation in the context of the competing theories to explain the SGRs
phenomenology: the magnetar and accretion-driven models. Based on the
ultra-relativistic, ultracompact X-ray binary model introduced in the
accompanying paper (Mosquera Cuesta 2004a), I present here a self-consistent
explanation for such an striking feature. I suggest that both the fundamental
mode and the overtones observed in SGR1900+14 stem from pulsations of a massive
white dwarf (WD). The fundamental mode (and likely some of its harmonics) is
excited because of the mutual gravitational interaction with its orbital
companion (a NS, envisioned here as point mass object) whenever the binary
Keplerian orbital frequency is a multiple integer number ($m$) of that mode
frequency (Pons et al. 2002). Besides, a large part of the powerful irradiation
from the fireball-like explosion occurring on the NS (after partial accretion
of disk material) is absorbed in different regions of the star driving the
excitation of other multipoles (Podsiadlowski 1991,1995), i.e., the overtones
(fluid modes of higher frequency). Part of this energy is then reemitted into
space from the WD surface or atmosphere. This way, the WD lightcurve carries
with it the signature of these pulsations inasmuch the way as it happens with
the Sun pulsations in Helioseismology. It is shown that our theoretical
prediction on the pulsation spectrum agrees quite well with the one found by
BeppoSAX (Feroci et al. 1999). A feature confirmed by numerical simulations
(Montgomery & Winget 2000).
