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A Very Low Luminosity X-Ray Flash: XMM-Newton Observations of GRB 031203

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posted on 2009-12-08, 16:24 authored by D. Watson, J. Hjorth, Andrew J. Levan, P. Jakobsson, Paul T. O'Brien, Julian P. Osborne, K. Pedersen, J. N. Reeves, J. A. Tedds, Simon A. Vaughan, M. J. Ward, Richard Willingale
GRB 031203 was observed by XMM-Newton twice, first with an observation beginning 6 hr after the burst and again after 3 days. The afterglow had average 0.2-10.0 keV fluxes for the first and second observations of img1.gif × 10-13 and img2.gif × 10-13 ergs cm-2 s-1, respectively, decaying very slowly according to a power law with an index of -0.55 ± 0.05. The prompt soft X-ray flux, inferred from a detection of the dust echo of the prompt emission, strongly implies that this burst is very soft and should be classified as an X-ray flash (XRF) and further, implies a steep temporal slope (lesssim-1.7) between the prompt and afterglow phases or in the early afterglow, very different from the later afterglow decay slope. A power law (Γ = 1.90 ± 0.05) with absorption at a level consistent with the Galactic foreground absorption fits the afterglow spectrum well. A bright low-redshift (z = 0.105) galaxy lies within 0farcs5 of the X-ray position and is likely to be the gamma-ray burst (GRB) host. At this redshift, GRB 031203 is the closest GRB or XRF known after GRB 980425. It has a very low equivalent isotropic gamma-ray energy in the burst (~3 × 1049 ergs) and X-ray luminosity in the afterglow (9 × 1042 ergs s-1 at 10 hr), 3-4 orders of magnitude less than typical bursts, though higher than either the faint XRF 020903 or GRB 980425. The rapid initial decline and subsequent very slow fading of the X-ray afterglow is also similar to that observed in GRB 980425, indicating that GRB 031203 may be representative of low-luminosity bursts.



Astrophysical Journal Letters, 2004, 605 (2), pp.101-104

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