Björnsson 2007 GRB060218的光学成分来自于同步自吸收

主要内容:
认为此暴和一般的暴差不多，只不过磁场比较强，洛仑兹因子比较低。然后同步字吸收频率比较高，使得光学和UV也在自吸收频率以下。

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文章信息:

arXiv:0709.1855 [ps, pdf, other]

Title: GRB 060218: The nature of the optical-UV component

Authors: C.-I. Björnsson (Stockholm Observatory)

Comments: 16 pages, 1 figure, accepted to ApJ

Subjects: Astrophysics (astro-ph)

The optical-UV component in GRB 060218 is assumed to be due to optically thick cyclotron emission. The key aspect of this model is the high temperature of the absorbing electrons. The heat input derives from nuclei accelerated in semi-relativistic internal shocks, like in ordinary gamma-ray bursts. Coulomb collisions transfer part of that energy to electrons. Inverse Compton cooling on the X-ray photons leads to electron temperatures around 100 keV. Such a high brightness temperature for the optical-UV emission implies an emitting area roughly equal to that of the thermal X-ray component. This suggests a model in which the radio, optical-UV and thermal X-ray emission are closely related: Although the optical-UV and thermal X-ray emission are two separate spectral components, it is argued that they both come from the photosphere of a quasi-spherical, continuous outflow, whose interaction with the circumstellar medium gives rise to the radio emission. The properties of GRB 060218, as measured in the co-moving frame, are similar to those of ordinary gamma-ray burst; i.e., the main difference is the much lower value of the bulk Lorentz factor in GRB 060218. The cyclotron absorption implies a magnetic field in rough equipartition with the matter energy density in the outflow. Hence, the magnetic field could have a dynamically important role, possibly with a magnetar as the central engine.