A Christmas burst

Last Christmas something exploded in the constellation of Andromeda. Well, that’s not quite true. This gamma-ray burst (named GRB 101225A) went off a long, long time ago, but the resulting flash finally arrived last year and were picked up by the SWIFT satellite (which then probably interrupted several festive lunches with its Burst Alert alarm).

This is a cross posting with the Astronomy Twitter Journal Club who are going to be discussing this topic on twitter (search for the #astrojc hashtag) this Thursday at 20:10 GMT. If you’re interested please come and join in.

Artist's impression (with festive enhancement) of a supernova explosion and resulting gamma-ray burst. Photo credit: NASA with apologies

The majority of gamma ray bursts are thought to be massive stellar explosions in distant galaxies, but the Christmas event didn’t fit this picture; the initial burst of gamma rays lasted for an unusually long time and, despite the efforts of powerful optical telescopes, no convincing candidate for the host galaxy could be found.

Nearly a year on from the initial observation two groups of astronomers have come up with two different, but equally plausible, explanations for the odd GRB 101225A. The first team suggest that it was caused by something small, like a comet, breaking apart and then falling into a neutron star within our own Milky Way. The alternative theory, put forward by the second team, also involves a neutron star, but in this case it’s merging with a young red giant star in another galaxy.

Unless the host of this gamma ray burst is found, and its distance measured, there’s no easy way to choose between these two options. Hopefully deeper optical data with, for example, a telescope like Hubble will provide the answers and settle this debate.

Thöne CC, de Ugarte Postigo A, Fryer CL, Page KL, Gorosabel J, Aloy MA, Perley DA, Kouveliotou C, Janka HT, Mimica P, Racusin JL, Krimm H, Cummings J, Oates SR, Holland ST, Siegel MH, De Pasquale M, Sonbas E, Im M, Park WK, Kann DA, Guziy S, García LH, Llorente A, Bundy K, Choi C, Jeong H, Korhonen H, Kubànek P, Lim J, Moskvitin A, Muñoz-Darias T, Pak S, & Parrish I (2011). The unusual γ-ray burst GRB 101225A from a helium star/neutron star merger at redshift 0.33. Nature, 480 (7375), 72-4 PMID: 22129726 (alternative link for the paper here)

Campana S, Lodato G, D’Avanzo P, Panagia N, Rossi EM, Della Valle M, Tagliaferri G, Antonelli LA, Covino S, Ghirlanda G, Ghisellini G, Melandri A, Pian E, Salvaterra R, Cusumano G, D’Elia V, Fugazza D, Palazzi E, Sbarufatti B, & Vergani SD (2011). The unusual gamma-ray burst GRB 101225A explained as a minor body falling onto a neutron star. Nature, 480 (7375), 69-71 PMID: 22129725 (alternative link for the paper here)

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