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Discovery of an X-ray afterglow associated with the γ-ray burst of 28 February 1997

Abstract

Establishing the nature of γ-ray bursts is one of the greatest challenges in high-energy astrophysics. The distribution of these bursts is isotropic across the sky, but inhomogeneous in space, with a deficit of faint bursts1. It is currently unknown whether γ-ray bursts are produced in our Galaxy or at cosmological distances. The detection and identification of counterparts at other wavelengths are seen as crucial for resolving the origin of the events. Here we report the detection by the Beppo-SAX satellite2 of an X-ray ‘afterglow’, associated with the γ-ray burst of 28 February 1997 (GRB970228; ref. 3)—the first such detection for any γ-ray burst. The X-ray transient was found to contain a significant fraction of the total energy of the γ-ray burst and, following the initial detection4 eight hours after the main burst, faded within a few days with a power-law decay function. The rapid locating of this γ-ray burst instigated a multi-wavelength observational campaign that culminated in the identification5 of a fading optical transient in a position consistent6 with the X-ray transient reported here.

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Figure 1: Time profile of GRB970228 in the γ-ray (from the Gamma-Ray Burst Monitor) and X-ray (from the Wide Field Camera) bands.
Figure 2: False-colour images of the source 1SAX J0501.
Figure 3: Variation of source flux with time in the 2–10keV range.

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Acknowledgements

This research is supported by the Italian Space Agency (ASI) and Consiglio Nazionale Ricerche of Italy. Beppo-SAX is a joint program of ASI and the Netherlands Agency for Aerospace Programs (NIVR). We thank the staff at the Beppo-SAX Scientific Operation Centre and the Operation Control Centre for their contributions to the GRB research program.

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Costa, E., Frontera, F., Heise, J. et al. Discovery of an X-ray afterglow associated with the γ-ray burst of 28 February 1997. Nature 387, 783–785 (1997). https://doi.org/10.1038/42885

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