Mildly relativistic X-ray transient 080109 and SN2008D: Towards a continuum from energetic GRB/XRF to ordinary Ibc SN
Abstract
We analyze the hitherto available space-based X-ray data as well as ground-based optical data of the X-ray transient 080109/SN2008D. From the data we suggest that (i) The initial transient ( 800 sec) is attributed to the reverse shock emission of a mildly relativistic ( a few) outflow stalled by the dense stellar wind. (ii) The subsequent X-ray afterglow ( 2× 104 sec) can be ascribed to the forward shock emission of the outflow, with a kinetic energy 1046 erg, when sweeping up the stellar wind medium. (iii) The late X-ray flattening ( 2× 104$ sec) is powered by the fastest non-decelerated component of SN2008D's ejecta. (iv) The local event rate of X-ray transient has a lower limit of 1.6× 104 yr-1 Gpc-3, indicating a vast majority of X-ray transients have a wide opening angle of 100 degree. The off-axis viewing model is less likely. (v) Transient 080109/SN2008D may lead to a continuum from GRB-SN to under-luminous GRB-/XRF-SN to X-ray transient-SN and to ordinary Ibc SN (if not every Ibc SN has a relativistic jet), as shown in Figure 2 of this Letter.