* Astronomy

Blobrana · L

GRB 101225A

Blobrana · L

NASA's Swift Finds a Gamma-Ray Burst With a Dual Personality

A peculiar cosmic explosion first detected by NASA's Swift observatory on Christmas Day 2010 was caused either by a novel type of supernova located billions of light-years away or an unusual collision much closer to home, within our own galaxy. Papers describing both interpretations appear in the Dec. 1 issue of the journal Nature.
The Christmas burst, also known as GRB 101225A, was discovered in the constellation Andromeda by Swift's Burst Alert Telescope at 1:38 p.m. EST on Dec. 25, 2010. The gamma-ray emission lasted at least 28 minutes, which is unusually long. Follow-up observations of the burst's afterglow by the Hubble Space Telescope and ground-based observatories were unable to determine the object's distance.
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Blobrana · L

Title: An unusual stellar death on Christmas Day
Authors: C. C. Thöne, A. de Ugarte Postigo, C. L. Fryer, K. L. Page, J. Gorosabel, D. A. Perley, C. Kouveliotou, H. T. Janka, M. A. Aloy, P. Mimica, J. L. Racusin, H. Krimm, J. Cummings, S. R. Oates, S. T. Holland, M. H. Siegel, M. De Pasquale, E. Sonbas, M. Im, W.-K. Park, D. A. Kann, S. Guziy, L. Hernandez Garcia, K. Bundy, A. J. Castro-Tirado, C. Choi, H. Jeong, H. Korhonen, P. Kubanek, J. Lim, A. Llorente, A. Moskvitin, T. Muñoz Darias, S. Pak, I. Parrish

Massive stars can end their lives in many different ways. Long Gamma-Ray Bursts (GRBs) are the most dramatic examples, releasing ultra-relativistic ejecta that produce non-thermal emission when interacting with the surrounding medium (Zhang et al. 2004). Usually, those events are accompanied by a supernova (SN) (Woosley et al. 2006). In a few low-redshift GRB-SNe we could observe the actual breakout of the shock front from the surface of the star (Campana et al. 2006). Here we present GRB 101225A, a very peculiar event at a distance of 1.6 Gpc. A bright X-ray transient with a thermal component and an unusual optical counterpart followed an exceptionally long gamma-ray event. During the first 10 days, the optical emission evolved as an expanding, cooling blackbody with a large initial radius, after which a faint SN was observed. The absence of a normal GRB afterglow implies that some dense material, likely ejected by the progenitor star, completely thermalised the high-energy emission. A possible progenitor is a helium star/neutron star binary which underwent a common envelope phase, expelling its hydrogen envelope prior to the explosion. The final merging process created a GRB-like event where we observe the shock breakout of the secondary star before the high-energy emission gets thermalised in the collision with the previously expelled shell, until finally the emission from the SN itself takes over. GRB 101225A defines a new, rare type of blackbody-dominated GRB which explodes in a dense environment created by the progenitor system itself.

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