Astrophys. J., 636, 967-970 (2006/January-2)
The soft X-ray blast in the apparently subluminous GRB 031203.
WATSON D., VAUGHAN S.A., WILLINGALE R., HJORTH J., FOLEY S., FYNBO J.P.U., JAKOBSSON P., LEVAN A., O'BRIEN P.T., OSBORNE J.P., PEDERSEN K., REEVES J.N., TEDDS J.A. and WATSON M.G.
Abstract (from CDS):
GRB 031203 was a very low apparent luminosity γ-ray burst (GRB). Coincidentally, it was also the first GRB with a dust-scattered X-ray halo. The observation of the halo allowed us to infer the presence of a large soft X-ray fluence in the total burst output. It has also been claimed, however, that GRB 031203 was intrinsically subenergetic, representative of a class of spectrally hard, low-energy bursts quite different from other GRBs. A careful reanalysis of the available data confirms our original finding that GRB 031203 had a very large soft X-ray component, the time of which can be constrained to within a few minutes after the burst, strongly suggesting that while GRB 031203 did indeed have a very low apparent luminosity, it was also very soft. Notions propagated in the literature regarding the uncertainties in the determination of the soft X-ray fluence from the halo data and on the available constraints from the hard X-ray data are addressed: the properties of the scattering dust along the line of sight (grain sizes, precise location, and geometry) are determined directly from the high-quality X-ray data so that there is little uncertainty about the scatterer; constraints on the X-ray light curve from the INTEGRAL spacecraft at the time of the soft X-ray blast are not complete because of a slew in the spacecraft pointing shortly after the burst. Claims that GRB 031203 was intrinsically underenergetic and that it represents a deviation from the luminosity-peak-energy relation do not appear to be substantiated by the data, regardless of whether the soft X-ray component is (arbitrarily) declared part of the prompt emission or the afterglow. We conclude that the difference between the soft and hard X-ray spectra from XMM-Newton and INTEGRAL indicate that a second soft pulse probably occurred in this burst, as has been observed in other GRBs, notably GRB 050502B.
Gamma Rays: Bursts - X-Rays: General - X-Rays: ISM
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