Late phase nebular spectra and photometry of Type Ib Supernova ( SN ) 2005bf taken by the Subaru telescope at \sim 270 and \sim 310 days since the explosion are presented .
Emission lines ( [ OI ] \lambda \lambda 6300 , 6363 , [ CaII ] \lambda \lambda 7291 , 7324 , [ FeII ] \lambda 7155 ) show the blueshift of \sim 1 , 500 - 2 , 000 km s ^ { -1 } .
The [ OI ] doublet shows a doubly-peaked profile .
The line luminosities can be interpreted as coming from a blob or jet containing only \sim 0.1 - 0.4 M _ { \odot } , in which \sim 0.02 - 0.06 M _ { \odot } is ^ { 56 } Ni synthesized at the explosion .
To explain the blueshift , the blob should either be of unipolar moving at the center-of-mass velocity v \sim 2 , 000 - 5 , 000 km s ^ { -1 } , or suffer from self-absorption within the ejecta as seen in SN 1990I .
In both interpretations , the low-mass blob component dominates the optical output both at the first peak ( \sim 20 days ) and at the late phase ( \sim 300 days ) .
The low luminosity at the late phase ( the absolute R magnitude M _ { R } \sim - 10.2 mag at \sim 270 days ) sets the upper limit for the mass of ^ { 56 } Ni \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ < $ } } 0.08 M% _ { \odot } , which is in contradiction to the value necessary to explain the second , main peak luminosity ( M _ { R } \sim - 18.3 mag at \sim 40 days ) .
Encountered by this difficulty in the ^ { 56 } Ni heating model , we suggest an alternative scenario in which the heating source is a newly born , strongly magnetized neutron star ( a magnetar ) with the surface magnetic field B _ { mag } \sim 10 ^ { 14 - 15 } gauss and the initial spin period P _ { 0 } \sim 10 ms. Then , SN 2005bf could be a link between normal SNe Ib/c and an X-Ray Flash associated SN 2006aj , connected in terms of B _ { mag } and/or P _ { 0 } .