[Show abstract][Hide abstract]ABSTRACT: Considering the contribution of emission from the host galaxies of gamma-ray bursts (GRBs) to radio afterglows, we investigate
the effect of host galaxies on observations statistically. For the three types of event, i.e. low-luminosity, standard and
high-luminosity GRBs, it is found that a tight correlation exists between the ratio of the radio flux (RRF) of the host galaxy
to the total radio peak emission and the observational frequency. Towards lower frequencies, in particular, the contribution
from the host increases significantly. The correlation can be used to obtain a useful estimate for the radio brightness of
those host galaxies that only have very limited radio afterglow data. Using this prediction, we reconsidered the theoretical
radio afterglow light curves for four kinds of event: high-luminosity, low-luminosity, standard and failed GRBs, taking into
account the contribution from host galaxies and aiming to explore the detectability of these events by the Five-hundred-metre
Aperture Spherical radio Telescope (FAST). Lying at a typical redshift of z = 1, most of the events can be detected easily by FAST. For the less fierce low-luminosity GRBs, their radio afterglows are
not strong enough to exceed the sensitivity limit of FAST at such distances. However, since a large number of low-luminosity
bursts actually happen very near to us, it is expected that FAST will still be able to detect many of them.
Full-text · Article · May 2015 · Monthly Notices of the Royal Astronomical Society
[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.
Full-text · Article · Feb 2014 · Research in Astronomy and Astrophysics
[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)
Preview · Article · Feb 2010 · Research in Astronomy and Astrophysics
[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.
Full-text · Article · Aug 2008 · Chinese Journal of Astronomy and Astrophysics