| GRB 051221A | |
| Event Type: | Gamma-ray burst |
| Detected By: | Swift |
| Discovery: | 5 billion years ago (detected 21 December 2005) |
| Duration: | 1.4 seconds |
| Redshift: | 0.5464 |
| Constellation: | Pegasus |
| Distance: | 5 billion ly |
GRB 051221A was a gamma ray burst (GRB) that was detected by NASA's Swift Gamma-Ray Burst Mission on December 21, 2005. The coordinates of the burst were α=, δ=, and it lasted about 1.4 seconds.[1] The same satellite discovered X-ray emission from the same object, andthe GMOS Instrument on the Gemini Observatory discovered an afterglow in the visible spectrum. This was observed for the next ten days, allowing a redshift of Z = 0.5464 to be determined for the host galaxy.[2]
The gamma ray emission from this object is of the variety known as a short-hard burst. The energy emission is consistent with the model of a merger by compact objects. It was the most distant short-hard burst found to that date for which a redshift could be determined.[2] The X-ray light curve showed evidence of three distinct breaks, possibly representing a strong energy injection.[3] The energy may have been injected by a millisecond magnetar. That is, a rapidly rotating pulsar with a strong magnetic field, estimated at 1014 gauss (1010 teslas).[4]