375 research outputs found
The EMBH model in GRB 991216 and GRB 980425
This is a summary of the two talks presented at the Rome GRB meeting by C.L.
Bianco and R. Ruffini. It is shown that by respecting the Relative Space-Time
Transformation (RSTT) paradigm and the Interpretation of the Burst Structure
(IBS) paradigm, important inferences are possible: a) in the new physics
occurring in the energy sources of GRBs, b) on the structure of the bursts and
c) on the composition of the interstellar matter surrounding the source.Comment: 8 pages, 3 figures, in the Proceedings of the "Third Rome Workshop on
Gamma-Ray Bursts in the Afterglow Era", 17-20 September 2002, M. Feroci, F.
Frontera, N. Masetti, L. Piro (editors
On the physical processes which lie at the bases of time variability of GRBs
The relative-space-time-transformation (RSTT) paradigm and the interpretation
of the burst-structure (IBS) paradigm are applied to probe the origin of the
time variability of GRBs. Again GRB 991216 is used as a prototypical case,
thanks to the precise data from the CGRO, RXTE and Chandra satellites. It is
found that with the exception of the relatively inconspicuous but
scientifically very important signal originating from the initial ``proper
gamma ray burst'' (P-GRB), all the other spikes and time variabilities can be
explained by the interaction of the accelerated-baryonic-matter pulse with
inhomogeneities in the interstellar matter. This can be demonstrated by using
the RSTT paradigm as well as the IBS paradigm, to trace a typical spike
observed in arrival time back to the corresponding one in the laboratory time.
Using these paradigms, the identification of the physical nature of the time
variablity of the GRBs can be made most convincingly. It is made explicit the
dependence of a) the intensities of the afterglow, b) the spikes amplitude and
c) the actual time structure on the Lorentz gamma factor of the
accelerated-baryonic-matter pulse. In principle it is possible to read off from
the spike structure the detailed density contrast of the interstellar medium in
the host galaxy, even at very high redshift.Comment: 11 pages, 5 figure
GRB 970228 Within the EMBH Model
We consider the gamma-ray burst of 1997 February 28 (GRB 970228) within the
ElectroMagnetic Black Hole (EMBH) model. We first determine the value of the
two free parameters that characterize energetically the GRB phenomenon in the
EMBH model, that is to say the dyadosphere energy,
ergs, and the baryonic remnant mass in units of ,
. Having in this way estimated the
energy emitted during the beam-target phase, we evaluate the role of the
InterStellar Medium (ISM) number density (n) and of the ratio between the effective emitting area and the total surface area of the GRB
source, in reproducing the observed profiles of the GRB 970228 prompt emission
and X-ray (2-10 keV energy band) afterglow. The importance of the ISM
distribution three-dimensional treatment around the central black hole is also
stressed in this analysis.Comment: 4 pages, 1 figure, to appear in the Proceedings of the Los Alamos
"Gamma Ray Burst Symposium" in Santa Fe, New Mexico, September 8-12 2003 (AIP
Conf. Ser.), CHAPTER: GRB Connection to Supernova
On the structures in the afterglow peak emission of gamma ray bursts
Using GRB 991216 as a prototype, it is shown that the intensity substructures observed in what is generally called the "prompt emission" in gamma ray bursts (GRBs) do originate in the collision between the accelerated baryonic matter (ABM) pulse with inhomogeneities in the interstellar medium (ISM). The initial phase of such process occurs at a Lorentz factor . The crossing of ISM inhomogeneities of sizes cm occurs in a detector arrival time interval of s implying an apparent superluminal behavior of . The long lasting debate between the validity of the external shock model vs. the internal shock model for GRBs is solved in favor of the first
New perspectives in physics and astrophysics from the theoretical understanding of Gamma-Ray Bursts
If due attention is given in formulating the basic equations for the
Gamma-Ray Burst (GRB) phenomenon and in performing the corresponding
quantitative analysis, GRBs open a main avenue of inquiring on totally new
physical and astrophysical regimes. This program is one of the greatest
computational efforts in physics and astrophysics and cannot be actuated using
shortcuts. A systematic approach has been highlighted in three paradigms: the
relative space-time transformation (RSTT) paradigm, the interpretation of the
burst structure (IBS) paradigm, the GRB-supernova time sequence (GSTS)
paradigm. In fundamental physics new regimes are explored: (1) the process of
energy extraction from black holes; (2) the quantum and general relativistic
effects of matter-antimatter creation near the black hole horizon; (3) the
physics of ultrarelativisitc shock waves with Lorentz gamma factor . In astronomy and astrophysics also new regimes are explored: (i) the
occurrence of gravitational collapse to a black hole from a critical mass core
of mass M\agt 10M_\odot, which clearly differs from the values of the
critical mass encountered in the study of stars ``catalyzed at the endpoint of
thermonuclear evolution" (white dwarfs and neutron stars); (ii) the extremely
high efficiency of the spherical collapse to a black hole, where almost 99.99%
of the core mass collapses leaving negligible remnant; (iii) the necessity of
developing a fine tuning in the final phases of thermonuclear evolution of the
stars, both for the star collapsing to the black hole and the surrounding ones,
in order to explain the possible occurrence of the "induced gravitational
collapse". A new class of space missions to acquire information on such extreme
new regimes are urgently needed.Comment: RevTeX4, 93 pages, 50 figures, to appear in the "Proceedings of the
Xth Brazilian School of Cosmology and Gravitation", M. Novello, editor, AIP,
in pres
A New Astrophysical "Triptych": GRB030329/SN2003dh/URCA-2
We analyze the data of the Gamma-Ray Burst/Supernova GRB030329/SN2003dh
system obtained by HETE-2 (GCN [1]), R-XTE (GCN [2]), XMM (Tiengo et al. [3])
and VLT (Hjorth et al. [4]) within our theory (Ruffini et al. [5] and
references therein) for GRB030329. By fitting the only three free parameters of
the EMBH theory, we obtain the luminosity in fixed energy bands for the prompt
emission and the afterglow (see Fig.1). Since the Gamma-Ray Burst (GRB)
analysis is consistent with a spherically symmetric expansion, the energy of
GRB030329 is E = 2.1 * 10^{52} erg, namely ~ 2 * 10^3 times larger than the
Supernova energy. We conclude that either the GRB is triggering an
induced-supernova event or both the GRB and the Supernova are triggered by the
same relativistic process. In no way the GRB can be originated from the
supernova. We also evidence that the XMM observations (Tiengo et al. [3]), much
like in the system GRB980425/SN1998bw (Ruffini et al. [6], Pian et al. [7]),
are not part of the GRB afterglow, as interpreted in the literature (Tiengo et
al. [3]), but are associated to the Supernova phenomenon. A dedicated campaign
of observations is needed to confirm the nature of this XMM source as a newly
born neutron star cooling by generalized URCA processes.Comment: 4 pages, 1 figure, to appear in the Proceedings of the Los Alamos
"Gamma Ray Burst Symposium" in Santa Fe, New Mexico, September 8-12 2003 (AIP
Conf. Ser.), CHAPTER: GRB03032
Antideuterons as a Signature of Supersymmetric Dark Matter
Once the energy spectrum of the secondary component is well understood,
measurements of the antiproton cosmic-ray flux at the Earth will be a powerful
way to indirectly probe for the existence of supersymmetric relics in the
galactic halo. Unfortunately, it is still spoilt by considerable theoretical
uncertainties. As shown in this work, searches for low-energy antideuterons
appear in the mean time as a plausible alternative, worth being explored. Above
a few GeV/n, a dozen spallation antideuterons should be collected by the future
AMS experiment on board ISSA. For energies less than about 3 GeV/n, the
antideuteron spallation component becomes negligible and may be supplanted by a
potential supersymmetric signal. If a few low-energy antideuterons are
discovered, this should be seriously taken as a clue for the existence of
massive neutralinos in the Milky Way.Comment: 16 pages, 9 figure
GRB 050315: A step toward the uniqueness of the overall GRB structure
Using the Swift data of GRB 050315, we progress on the uniqueness of our theoretically predicted Gamma-Ray Burst (GRB) structure as composed by a proper-GRB (P-GRB), emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the so called "prompt emission" as due to external shocks. Thanks to the Swift observations, the P-GRB is identified and for the first time we can theoretically fit detailed light curves for selected energy bands on a continuous time scale ranging over 10^6 seconds. The theoretically predicted instantaneous spectral distribution over the entire afterglow is presented, confirming a clear hard-to-soft behavior encompassing, continuously, the "prompt emission" all the way to the latest phases of the afterglow
Positrons from particle dark-matter annihilation in the Galactic halo: propagation Green's functions
We have made a calculation of the propagation of positrons from dark-matter
particle annihilation in the Galactic halo in different models of the dark
matter halo distribution using our 3D code, and present fits to our numerical
propagation Green's functions. We show that the Green's functions are not very
sensitive to the dark matter distribution for the same local dark matter energy
density. We compare our predictions with computed cosmic ray positron spectra
(``background'') for the ``conventional'' CR nucleon spectrum which matches the
local measurements, and a modified spectrum which respects the limits imposed
by measurements of diffuse Galactic gamma-rays, antiprotons, and positrons. We
conclude that significant detection of a dark matter signal requires favourable
conditions and precise measurements unless the dark matter is clumpy which
would produce a stronger signal. Although our conclusion qualitatively agrees
with that of previous authors, it is based on a more realistic model of
particle propagation and thus reduces the scope for future speculations.
Reliable background evaluation requires new accurate positron measurements and
further developments in modelling production and propagation of cosmic ray
species in the Galaxy.Comment: 8 pages, 6 ps-figures, 3 tables, uses revtex. Accepted for
publication in Physical Review D. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Positron Propagation and Fluxes from Neutralino Annihilation in the Halo
Supersymmetric neutralinos are one of the most promising candidates for the
dark matter in the Universe. If they exist, they should make up some fraction
of the Milky Way halo. We investigate the fluxes of positrons expected at the
Earth from neutralino annihilation in the halo. Positron propagation is treated
in a diffusion model including energy loss. The positron source function
includes contributions from both continuum and monochromatic positrons. We find
that, for a "canonical" halo model and propagation parameters, the fluxes are
generally too low to be visible. Given the large uncertainties in both
propagation and halo structure, it is however possible to obtain observable
fluxes. We also investigate the shapes of the positron spectra, including fits
to a feature indicated by the results of the HEAT experiment.Comment: 16 pages, 19 figures, uses revte
- …