Context : Observations of gamma-ray bursts ( GRBs ) have shown an hybridization between the two classes of long and short bursts .
In the context of the fireshell model , the GRB light curves are formed by two different components : the proper GRB ( P-GRB ) and the extended afterglow .
Their relative intensity is linked to the fireshell baryon loading B .
The GRBs with P-GRB predominance are the short ones , the remainders are long .
A new family of disguised short bursts has been identified : long bursts with a protracted low instantaneous luminosity due to a low density CircumBurst Medium ( CBM ) .
In the 15 – 150 keV energy band GRB 071227 exhibits a short duration ( about 1.8 s ) spike-like emission followed by a very soft extended tail up to one hundred seconds after the trigger .
It is a faint ( E _ { iso } = 5.8 \times 10 ^ { 50 } ) nearby GRB ( z = 0.383 ) that does not have an associated type Ib/c bright supernova ( SN ) .
For these reasons , GRB 071227 has been classified as a short burst not fulfilling the Amati relation holding for long burst .

Aims : We check the classification of GRB 071227 provided by the fireshell model .
In particular , we test whether this burst is another example of a disguised short burst , after GRB 970228 and GRB 060614 , and , for this reason , whether it fulfills the Amati relation .

Methods : We simulate GRB 071227 light curves in the Swift BAT 15 – 50 keV bandpass and in the XRT ( 0.3 – 10 keV ) energy band within the fireshell model .

Results : We perform simulations of the tail in the 15 – 50 keV bandpass , as well as of the first part of the X-ray afterglow .
This infers that : E _ { tot } ^ { e ^ { \pm } } = 5.04 \times 10 ^ { 51 } erg , B = 2.0 \times 10 ^ { -4 } , E _ { P - GRB } / E _ { aft } \sim 0.25 , and \langle n _ { cbm } \rangle = 3.33 particles/cm ^ { 3 } .
These values are consistent with those of “ long duration ” GRBs .
We interpret the observed energy of the first hard emission by identifying it with the P-GRB emission .
The remaining long soft tail indeed fulfills the Amati relation .

Conclusions : Previously classified as a short burst , GRB 071227 on the basis of our analysis performed in the context of the fireshell scenario represents another example of a disguised short burst , after GRB 970228 and GRB 060614 .
Further confirmation of this result is that the soft tail of GRB 071227 fulfills the Amati relation .