Swift时代伽马射线暴的观测和理论

Observations and Theories of GRBs in the Swift Era

伽马射线暴是宇宙中最剧烈的爆发现象之一。Swift卫星的快速定位和Fermi卫星的宽、高能段观测,使得伽马暴的观测可以全波段进行。通过Swift的观测可以对伽马暴现象的本质有进一步的理解,而Fermi卫星提供了一些暴高能光子的辐射数据,为进一步研究暴的辐射机制和伽马暴以及它的余辉提供了有力的依据。介绍了Swift和Fermi卫星发射后一些伽马暴的观测和理论研究进展。

Gamma-ray bursts（GRBs） are the most luminous phenomenon in the universe, and their origin and mechanism are very active areas of research and debate.Through nearly forty years development,today,gamma-ray bursts are accessible in full time window and in all electromagnetic wavelengths of the events,with the satellites Swift and Fermi.Swift,the NASA＇s dedicated GRB emission,was launched on 20th November 2004.With three instruments,Bursts Alert Telescope（BAT）,X-ray Telescope（XRT） and UV-Optical Telescope（UVOT）,Swift can ＂swiftly＂ catch the unpredictable bursts of gamma-ray in random direction of the sky within less than 100 s.With its rapid-response capability and multi-wavelength observatory,the swift satellite has provided high-quality observations of hundreds of bursts,and facilitated a wide range of follow-up observations within seconds of each event.Swift has brought new surprises and challenges to our understanding of cosmological GRBs.The major discoveries of Swift can be concluded as following four points.First discovery is the identification of a canonical X-ray afterglow behavior.Besides the prompt emission phase,there are five components in the X-ray light curves,that are,the steep decay phase,the shallow decay phase,the normal decay phase and the post jet break phase.The other one is the discovery and the location of some short bursts, which enabled much more detailed studies of the bursts environment,the host galaxy,and the intergalactic,and favored the idea that short bursts are related to mergers of two compact stellar objects.Thirdly,Swift observations showed faint soft gamma-ray extensions or tails of some short GRBs,which means that they are not necessarily short.The traditional ＂short long＂ classification regime breaks down,and another criteria is needed in order to define the two GRB categories.The fourth discovery of Swift is the detection of GRBs with redshift.GRB090423 has the unprecedented high redshift of z（？）8.2,and the mean redshift of the Swift bursts is2,which is a factor（？）2 higher than the mean of the BeppoSAX and GETE-2 redshifts.The detection of a long burst,GRB060218,is also the exciting result from Swift for it is the first time that a GRB/SN has been observed minutes after the gamma-ray trigger at X-ray and UV/optical wavelengths. The Fermi gamma-ray space telescope,includes two instruments,Gamma-ray Bursts Montior （GBM） and Large Area Telescope（LAT）,launched on 11th June 2008.Fermi has opened a new high-energy window in the study of GRBs and provided a powerful tool for study of the radiation mechanisms and the physical conditions for GRBs and their afterglows.