Could the GRB-Supernovae GRB 031203 and XRF 060218 be Cosmic Twins?
  The gamma-ray burst (GRB) / X-ray flash (XRF) events GRB 031203, discovered
by INTEGRAL, and XRF 060218, discovered by Swift, represent two of only five
GRB-SNe with optical spectroscopic confirmation of their SN components. Yet
their observed high-energy properties offer a sharp contrast: While GRB 031203
was detected as a short 40-s burst with a spectrum peaking at E_peak > 190 keV,
XRF 060218 was a T_90 ~ 2100-s long, smoothly-evolving burst with peak energy
E_peak = 4.9 keV. At the same time, the properties of the two expanding
dust-scattered X-ray halos observed in a fast-response XMM-Newton observation
of GRB 031203 reveal that this event was accompanied by an "X-ray blast" with
fluence comparable to or greater than that of the prompt gamma-ray event.
Taking this observation as our starting point, we investigate the likely
properties of the X-ray blast from GRB 031203 via detailed modeling of the XMM
data, discovering a third halo due to scattering off a more distant dust sheet
at d_3 = 9.94 +/- 0.39 kpc, and constraining the timing of the X-ray blast
relative to the GRB trigger time to be t_0 = 11 +/- 417 s. Using our
constraints, we compare the properties of GRB 031203 to those of other GRB-SNe
in order to understand the likely nature of its X-ray blast, concluding that a
bright X-ray flare, as in GRB 050502B, or shock breakout event, as in XRF
060218, provide the most likely explanations. In the latter case, we consider
the added possibility that XRF 060218 may have manifested an episode of bright
gamma-ray emission prior to the burst observed by Swift, in which case GRB
031203 and XRF 060218 would be "cosmic twin" explosions with nearly identical
high-energy properties.
