  It has been argued that the long gamma-ray burst (GRB) of GRB 060614 without
an associated supernova (SN) has challenged the current classification and fuel
model for long GRBs, and thus a tidal disruption model has been proposed to
account for such an event. Since it is difficult to detect SNe for long GRBs at
high redshift, the absence of an SN association cannot be regarded as the solid
criterion for a new classification of long GRBs similar to GRB 060614, called
GRB 060614-type bursts. Fortunately, we now know that there is an obvious
periodic substructure observed in the prompt light curve of GRB 060614. We thus
use such periodic substructure as a potential criterion to categorize some long
GRBs into a new class of bursts, which might have been fueled by an
intermediate-mass black hole (IMBH) gulping a star, rather than a massive star
collapsing to form a black hole. Therefore, the second criterion to recognize
for this new class of bursts is whether they fit the tidal disruption model.
From a total of 328 Swift GRBs with accurately measured durations and without
SN association, we find 25 GRBs satisfying the criteria for GRB 060614-type
bursts: seven of them are with known redshifts and 18 with unknown redshifts.
These new bursts are ~6% of the total Swift GRBs, which are clustered into two
subclasses: Type I and Type II with considerably different viscous parameters
of accretion disks formed by tidally disrupting their different progenitor
stars. We suggest that the two different kinds of progenitors are solar-type
stars and white dwarfs: the progenitors for four Type I bursts with viscous
parameter of around 0.1 are solar-type stars, and the progenitors for 21 Type
II bursts with viscous parameter of around 0.3 are white dwarfs. The potential
applications of this new class of GRBs as cosmic standard candles are discussed
briefly
