322 research outputs found
The Supercritical Pile GRB Model: The Prompt to Afterglow Evolution
The "Supercritical Pile" is a very economical GRB model that provides for the
efficient conversion of the energy stored in the protons of a Relativistic
Blast Wave (RBW) into radiation and at the same time produces - in the prompt
GRB phase, even in the absence of any particle acceleration - a spectral peak
at energy MeV. We extend this model to include the evolution of the
RBW Lorentz factor and thus follow its spectral and temporal features
into the early GRB afterglow stage. One of the novel features of the present
treatment is the inclusion of the feedback of the GRB produced radiation on the
evolution of with radius. This feedback and the presence of kinematic
and dynamic thresholds in the model are sources of potentially very rich time
evolution which we have began to explore. In particular, one can this way
obtain afterglow light curves with steep decays followed by the more
conventional flatter afterglow slopes, while at the same time preserving the
desirable features of the model, i.e. the well defined relativistic electron
source and radiative processes that produce the proper peak in the spectra. In this note we present the results of a specific set of
parameters of this model with emphasis on the multiwavelength prompt emission
and transition to the early afterglow.Comment: 11 pages, 4 figures, accepted for publication in ApJ Letter
On the numerical analysis of triplet pair production cross-sections and the mean energy of produced particles for modelling electron-photon cascade in a soft photon field
The double and single differential cross-sections with respect to positron
and electron energies as well as the total cross-section of triplet production
in the laboratory frame are calculated numerically in order to develop a Monte
Carlo code for modelling electron-photon cascades in a soft photon field. To
avoid numerical integration irregularities of the integrands, which are
inherent to problems of this type, we have used suitable substitutions in
combination with a modern powerful program code Mathematica allowing one to
achieve reliable higher-precission results. The results obtained for the total
cross-section closely agree with others estimated analytically or by a
different numerical approach. The results for the double and single
differential cross-sections turn out to be somewhat different from some
reported recently. The mean energy of the produced particles, as a function of
the characteristic collisional parameter (the electron rest frame photon
energy), is calculated and approximated by an analytical expression that
revises other known approximations over a wide range of values of the argument.
The primary-electron energy loss rate due to triplet pair production is shown
to prevail over the inverse Compton scattering loss rate at several (2)
orders of magnitude higher interaction energy than that predicted formerly.Comment: 18 pages, 8 figures, 2 tables, LaTex2e, Iopart.cls, Iopart12.clo,
Iopams.st
On the multiwavelength emission from Gamma Ray Burst afterglows
Aims: Drawing an analogy with Active Galactic Nuclei, we investigate the
one-zone SSC model of Gamma Ray Bursts afterglows in the presence of electron
injection and cooling both by synchrotron and SSC losses. Methods: We solve the
spatially averaged kinetic equations which describe the simultaneous evolution
of particles and photons, obtaining the multi-wavelength spectrum as a function
of time. We back up our numerical calculations with analytical solutions of the
equations using various profiles of the magnetic field evolution under certain
simplifying assumptions. Results: We apply the model to the afterglow evolution
of GRBs in a uniform density environment and examine the impact various
parameters have on the multiwavelength spectra. We find that in cases where the
electron injection and/or the ambient density is high, the losses are dominated
by SSC and the solutions depart significantly from the ones derived in the
synchrotron standard cases.Comment: 12 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
Is There a Disc in the Superluminal Quasars?
We present a new evidence of the accretion disc in active galactic nuclei, by
examining the properties of the Ha emission line versus viewing angle, in a
sample of superluminal (SL) quasars. Both line velocity width (FWHM) and rest
equivalent width (EW) correlate with viewing angle. These correlations are
quantitatively consistent with a disc geometry for both the line and the
underlying continuum source.Comment: 18 pages with 6 figures, accepted for publication in MNRA
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