Could the GRB-supernovae GRB031203 and XRF060218 be cosmic twins?

The gamma-ray burst (GRB)/X-ray flash (XRF) events GRB031203, discovered by INTEGRAL, and XRF060218, discovered by Swift, represent two of the only five GRB-supernovae (GRB-SNe) with optical spectroscopic confirmation of their SN components. Yet, their observed high-energy properties offer a sharp contrast: while GRB031203 was detected as a short 40 s burst with a spectrum peaking at E_peak > 190keV, XRF060218 was a T₉₀ ~ 2100 s long, smoothly evolving burst with peak energy E_peak = 4.9keV. At the same time, the properties of the two expanding dust-scattered X-ray haloes observed in a fast-response XMM-Newton observation of GRB031203 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 GRB031203 via detailed modelling of the XMM data, discovering a third halo due to scattering off a more distant dust sheet at d<sub>3</sub> = 9.94 +/- 0.39kpc, and constraining the timing of the X-ray blast relative to the GRB trigger time to be t<sub>0</sub> = 11 +/- 417s. Using our constraints, we compare the properties of GRB031203 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 GRB050502B, or shock breakout event, as in XRF060218, provides the most likely explanation. In the latter case, we consider the added possibility that XRF060218 may have manifested an episode of bright gamma-ray emission prior to the burst observed by Swift, in which case GRB031203 and XRF060218 would be `cosmic twin' explosions with nearly identical high-energy properties.