[Show abstract][Hide abstract] ABSTRACT: Using the generic hydrodynamic model of Gamma-Ray Burst (GRB) afterglows, we
calculate the radio afterglow light curves of low luminosity, high luminosity,
failed and standard GRBs in different observational bands of FAST's energy
window. The GRBs are assumed to be located at different distances from us. Our
results show that the possibilities of detecting GRB radio afterglows decrease
in order for high luminosity, standard, failed and low luminosity GRBs
correspondingly. We predict that almost all types of radio afterglows except
that of low luminosity GRBs could be observed by the worldwide largest radio
telescope as long as the domains of time and frequency are appropriate. It is
important to note that FAST can detect relatively weak radio afterglows at a
higher frequency of 2.5 GHz for very high redshift up to z=15 or even more.
Radio afterglows of low luminosity GRBs can be detected only if FAST is
available in its second phase. We expect that FAST will largely expand the
current sample of GRB radio afterglows in the near future.
[Show abstract][Hide abstract] ABSTRACT: Multiple rebrightenings have been observed in the multiband afterglow of GRB 030329. Especially, a marked and quick rebrightening occurred at about t ~ 1.2 * 10^5 s. Energy injection from late and slow shells seems to be the best interpretation for these rebrightenings. Usually it is assumed that the energy is injected into the whole external shock. However, in the case of GRB 030329, the rebrightenings are so quick that the usual consideration fails to give a satisfactory fit to the observed light curves. Actually, since these late/slow shells coast freely in the wake of the external shock, they should be cold and may not expand laterally. The energy injection then should only occur at the central region of the external shock. Considering this effect, we numerically re-fit the quick rebrightenings observed in GRB 030329. By doing this, we were able to derive the beaming angle of the energy injection process. Our result, with a relative residual of only 5% - 10% during the major rebrightening, is better than any previous modeling. The derived energy injection angle is about 0.035. We assume that these late shells are ejected by the central engine via the same mechanism as those early shells that produce the prompt gamma-ray burst. The main difference is that their velocities are much slower, so that they catch up with the external shock very lately and manifest as the observed quick rebrightenings. If this were true, then the derived energy injection angle can give a good measure of the beaming angle of the prompt gamma-ray emission. Our study may hopefully provide a novel method to measure the beaming angle of gamma-ray bursts. Comment: 8 pages, 6 figures, Has been accepted by RAA (Research in Astronomy and Astrophysics)
Research in Astronomy and Astrophysics 02/2010; · 1.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: When the axis of a gamma-ray burst (GRB) does not coincide with the spin axis of its source, there may result a ring-shaped jet. Using some refined jet dynamics, we calculate multi-wavelength afterglow light curves for such ring-shaped jets. In the R-band we find an obvious break in the afterglow light curve due to the beaming effect and the break is affected by many parameters, such as the electron energy fraction ξe, the magnetic energy fraction ξB2, the width of ring Δθ and the medium number density n. The overall light curve can be divided into three power-law stages, i.e., an ultra-relativistic stage, an after-break stage and a deep Newtonian stage. For each stage the power-law index is larger in the ring-shaped jet than in the corresponding conical jet.
Chinese Journal of Astronomy and Astrophysics 08/2008; 8(4):411. · 0.89 Impact Factor