- Polarization light curves and position angle variation
of beamed gamma-ray bursts
Gabriele Ghisellini & Davide Lazzati
MNRAS, 309, L7 (1999)
In this paper we present a model for the origin
and evolution of linear polarization from beamed GRB jets. Net polarization
is observed if the line of sight does not coincide with the jet symmetry
axis. The polarization-curve is characterized by two maxima separated by
a moment of null polarization that coincides with the break time in the light-curve.
At the moment of null polarization the position angle rotates abruptly by
90 degrees.
- Iron line in the afterglow: a key to unveil gamma-ray burst
progenitors
Davide Lazzati, Sergio Campana & Gabriele Ghisellini
MNRAS, 304, L31 (1999)
This is the first paper ever presented on the
interpretation of iron emission lines in the early afterglow of GRBs. We
consider a model in which part of the GRB and early afterglow photons are
re-processed into lines by material at ~1 light day from the source. Several
radiation mechanism are considered, the more promising being reflection from
a cold slab of material. Limits for the involved mass of iron are derived.
- Compton-dragged Gamma-Ray Bursts Associated with Supernovae
Davide Lazzati, Gabriele Ghisellini, Annalisa Celotti &
Martin J. Rees
ApJ, 529, L17 (2000)
We consider Compton Drag (inverse compton emission
powered by the bulk kinetic energy of the flow) as a mechanism for the preduction
of the prompt gamma-ray phtons in GRBs. The possibility is particularly intriguing
if GRBs are associated with SN explosions that can provide a large amount
of soft seed photons of the correct energy. We show that this mechanism
can explain the energetics of GRBs, can in principle give very high efficiencies
(compared to internal shocks) and explain the lightcurve variability witout
invoking extreme inhomegeneities of the flow.
- Possible detection of hard X-ray afterglows of short gamma
-ray bursts
Davide Lazzati, Enrico Ramirez-Ruiz & Gabriele Ghisellini
A&A, 379, L39 (2001)
We present an analysis of the BATSE lightcurve
of 76 bright short-hard GRBs. The analysis is aimed at detecting possible
tails of emission after the prompt GRB phase. We detect the presence of excess
emission in the softer channels of BATSE in the coadded background subtracted
lightcurve. The hardness ratio reveals that this emission tails is softer
than typical GRB lightcurves, suggesting that this emission is better characterized
as an afterglow component.
- Time-dependent photoionization in a dusty medium - III. The
effect of dust on the photoionization of metals
Davide Lazzati & Rosalba Perna
MNRAS, 340, 694 (2003)
We study the time-dependent evolution of opacity
of a cloud of ISM suddenly illuminated by a powerful source of light. The
ISM is composed by a mixture of dust grains (silicates and graphite) and
gas. Dust destruction and photoionization are followed and the dependence
of the opacity evolution on the source spectrum is analyzed in detail.