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GRB 080319B was a very bright gamma‐ray burst with a total isotropic energy ∼1054 erg. It was also distinguished by the strong prompt optical emission with a peak magnitude ∼5th. In this work we interpret the prompt optical (soft γ—ray) emission as the synchrotron (synchrotron self‐Compton) radiation of internal shocks at a rather large radius ∼1016 cm. In this model, the GRB outflow is baryonic rather than Poynting‐flux dominated. The 2nd‐order Inverse Compton radiation of the internal shocks may have not been effectively suppressed and a GeV‐TeV flare as energetic as the keV—MeV emission is plausible, which is detectable by a satellite like GLAST or AGILE.

Before 2004, nearly all GRB afterglow data could be understood in the context of the external shocks model. This situation has changed in the past two years, when it became clear that some afterglow components should be attributed to the activity of the central engine; i.e., the {\it central engine afterglow}. We review here the afterglow emission that is directly related to the GRB central engine. Such an interpretation proposed by Katz, Piran & Sari, peculiar in pre-{\it Swift} era, has become generally accepted now., 4 pages including 1 figure. Presented at the conference "Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China)

Line‐shaped plasma was produced by ablating plasma from multi‐groove Aluminum surface of a groove period of 100 μm, on which the direction of groove (50 μm in depth and 50 μm in width) is perpendicular to the focal line of 1.05 μm 120 ps (FWHM) heating laser. Comparison with the results of flat‐slab target, different spatial profiles of electron density and temperature and line emission intensity were found. Enhancement of on‐axis emission of candidate lasing line of Al10+which maybe originate from enhanced GL value were observed.

We will report recent progress on shorter wavelength recombination X‐ray laser research at SIOFM, including the observation of lasing at 46.8 A of the lithium‐like Ti19+ 4f‐3d transition, which was conducted at LF12 laser facility of SIOFM with Ti slab targets driven by an about 110 ps‐duration FWHM quasi‐Gaussian pulse (λ=1.05 μm). Comparison of long‐pulse (∼900 ps) and short pulse (∼110) driving Li‐like Si and Ca ions and H‐like F ion recombination X‐ray lasers will also be presented.

Presented are time‐ and space‐resolved investigation of recombination x‐ray lasers. An improved method for gain determination was put forward, by which the laser gain of the Li‐like Si 4f‐3d transition at 13.0 nm was measured, which is in good agreement with theoretical simulation. Plasma parameters of electron density and temperature estimated from spectral Stark broadening and characteristic recombination time, respectively, were in qualitative agreement with the plasma conditions given by the theory for the 4f‐3d gain.

Spectral diagnostic technique was used to study the properties of line‐shaped laser plasmas. Electron temperature and electron density profiles were deduced from the spectra obtained by a pinhole crystal spectrograph. The Stark‐broadened line‐wings of hydrogenic ions were used to deduce the electron density beyond the critical surface, and the results were compared with the theoretical model of planar laser‐driven ablation. Time integrated properties of line‐shaped laser plasma were also discussed and compared with those of spot‐shaped laser plasma and the laser absorption theoretical estimations.

A program was developed using the Marquardt algorithm method to fit the Stark‐broadened line wings of hydrogenic ions, which can be conveniently used to measure electron density in laser‐produced plasma. Applications of the method are illustrated using space‐resolved 2p‐1s resonance lines in line‐shaped laser plasmas of Mg slab targets irradiated with different laser intensity. Space‐resolved electron densities higher than the critical density are obtained by fitting the Stark‐broadened line wings with the program.