4,021 research outputs found
The vicissitudes of "cannonballs": a response to criticisms by A.M. Hillas and a brief review of our claims
A.M. Hillas, in a review of the origins of cosmic rays, has recently
criticized the "cannonball" (CB) model of cosmic rays and gamma-ray bursts. We
respond to this critique and take the occasion to discuss the crucial question
of particle acceleration in the CB model and in the generally accepted models.
We also summarize our claims concerning the CB model.Comment: 3.3 pages, no figure
Is the diffuse gamma background radiation generated by galactic cosmic rays?
We explore the possibility that the diffuse gamma-ray background radiation
(GBR) at high galactic latitudes could be dominated by inverse Compton
scattering of cosmic ray (CR) electrons on the cosmic microwave background
radiation and on starlight from our own galaxy. Assuming that the mechanisms
accelerating galactic CR hadrons and electrons are the same, we derive simple
and successful relations between the spectral indices of the GBR above a few
MeV, and of the CR electrons and CR nuclei above a few GeV. We reproduce the
observed intensity and angular dependence of the GBR, in directions away from
the galactic disk and centre, without recourse to hypothetical extragalactic
sources.Comment: Submitted for publicatio
The Cannonball Model of Gamma Ray Bursts: Lines in the X-Ray Afterglow
Recent observations suggest that gamma-ray bursts (GRBs) and their afterglows
are produced by jets of highly relativistic cannonballs (CBs), emitted in
supernova explosions. The fully ionized CBs cool to a temperature below 4500 K
within a day or two, at which point electron-proton recombination produces an
intense Lyman- emission. The line energy is Doppler-shifted by the CBs'
motion to X-ray energies in the observer's frame. The measured line energies,
corrected for their cosmological redshift, imply Doppler factors in the range
600 to 1000, consistent with those estimated -in the CB model- from the
characteristics of the -ray bursts. All other observed properties of
the lines are also well described by the CB model. Scattering and
self-absorption of the recombination lines within the CB also produce a
wide-band flare-up in the GRB afterglow, as the observations indicate. A very
specific prediction of the CB model is that the X-ray lines ought to be narrow
and move towards lower line energies as they are observed: their current
apparently large widths would be the effect of time integration, and/or of the
blending of lines from CBs with different Doppler factors.Comment: 8 pages, no figure
The threat to life from Eta Carinae and gamma ray bursts
Eta Carinae, the most massive and luminous star known in our galaxy, is
rapidly boiling matter off its surface. At any time its core could collapse
into a black hole, which may result in a gamma-ray burst (GRB) that can
devastate life on Earth. Auspiciously, recent observations indicate that the
GRBs are narrowly beamed in cones along the rotational axis of the progenitor
star. In the case of Eta Carinae the GRBs will not point to us, but will be
ravaging to life on planets in our galaxy that happen to lie within the two
beaming cones. The mean rate of massive life extinctions by jets from GRBs, per
life-supporting planet in galaxies like ours, is once in 100 million years,
comparable to the rate of major extinctions observed in the geological records
of our planet.Comment: Published in Astrophysics and Gamma Ray Physics in Space (eds. A.
Morselli and P. Picozza), Frascati Physics Series Vol. XXIV (2002), pp.
513-52
The time ending the shallow decay of the X-ray light curves of long GRBs
We show that the mean values and distributions of the time ending the shallow
decay of the light curve of the X-ray afterglow of long gamma ray bursts
(GRBs), the equivalent isotropic energy in the X-ray afterglow up to that time
and the equivalent isotropic GRB energy, as well as the correlations between
them, are precisely those predicted by the cannonball (CB) model of GRBs.
Correlations between prompt and afterglow observables are important in that
they test the overall consistency of a GRB model. In the CB model, the prompt
and afterglow spectra, the endtime, the complex canonical shape of the X-ray
afterglows and the correlations between GRB observables are not surprises, but
predictions.Comment: 12 pages, 4 figure
Origin of the Ultrahigh-Energy Cosmic Rays and their Spectral Break
The energy spectrum, composition and arrival directions of ultrahigh energy
cosmic rays (UHECRs) with energy above the cosmic ray ankle, measured by the
Pierre Auger Observatory, are inconsistent if their origin is assumed to be
extragalactic. Their observed properties, however, are those expected from
UHECRs accelerated by the highly relativistic jets emitted in Galactic gamma
ray bursts, most of which are beamed away from Earth. If this alternative
interpretation is correct, the observed break in the energy spectrum of UHECRs
around 50 EeV is not the Greisen-Zatsepin-Kuzmin cutoff but the energy
threshold for free escape of ultrahigh energy iron cosmic rays from the Galaxy
and above their respective free-escape threshold-energies, UHECR nuclei should
point back to their Galactic sources or their remnants rather than to active
galactic nuclei (AGN) within the GZK horizon.Comment: Invited talk presentet by A. Dar at the Rencontre de La Thuile, 2011.
To be published in Nuovo Ciment
A common origin of all the species of high-energy cosmic rays?
Cosmic ray nuclei, cosmic ray electrons with energy above a few GeV, and the
diffuse gamma-ray background radiation (GBR) above a few MeV, presumed to be
extragalactic, could all have their origin or residence in our galaxy and its
halo. The mechanism accelerating hadrons and electrons is the same, the
electron spectrum is modulated by inverse Compton scattering on starlight and
on the microwave background radiation; the -rays are the resulting
recoiling photons. The spectral indices of the cosmic-ray electrons and of the
GBR, calculated on this simple basis, agree with observations. The angular
dependence and the approximate magnitude of the GBR are also explained.Comment: Includes a discussion of the contribution of inverse Compton
scattering of CR electrons by starlight in the halo to the gamma background
radiation. One corrected typo. Additional references, and figures to compare
predictions for the angular dependence of the gamma background radiation with
data. Conclusions are unchange
On the origin of the diffuse gamma-ray background radiation
We show that inverse Compton scattering of cosmic-microwave-background and
starlight photons by cosmic-ray electrons in the interstellar and intergalactic
space explains well the spectrum and intensity of the diffuse gamma-ray
background radiation (GBR), which was measured by EGRET aboard the Compton
Gamma Ray Observatory (CGRO) in directions away from the Galactic disk and
centre. The Gamma Ray Large Area Space Telescope (GLAST) will be able to
separate the Galactic foreground from the extragalactic gamma-rays, and to
provide stringent tests of the theory
On the Polarization of Gamma Ray Bursts and their Optical Afterglows
The polarization of the optical afterglow (AG) of Gamma-Ray Bursts (GRBs) has
only been measured in a few instances at various times after the GRB. In all
cases except the best measured one (GRB 030329) the observed polarization and
its evolution are simple and easy to explain in the most naive version of the
"Cannonball'' model of GRBs: the "intrinsic" AG polarization is small and the
observations reflect the "foreground" effects of the host galaxy and ours. The
polarization observed in GRB 030329 behaves chaotically, its understanding
requires reasonable but ad-hoc ingredients. The polarization of the gamma rays
of a GRB has only been measured in the case of GRB 021206. The result is
debated, but similar measurements would be crucial to the determination of the
GRB-generating mechanism.Comment: 10 pages, 13 figure
Is there a 1998bw-like supernova in the afterglow of gamma ray burst 011121?
We use the very simple and successful Cannonball Model (CB) of gamma ray
bursts (GRBs) and their afterglows (AGs) to analyze the observations of the
strongly extinct optical AG of the relatively nearby GRB 011121, which were
made with ground-based telescopes at early times, and with the HST at later
time. We show that GRB 011121 was indeed associated with a 1998bw-like
supernova at the GRB's redshift, as we had specifically predicted for this GRB
before the supernova could be observed.Comment: Submitted for publicatio
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