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Remo Ruffini

Publications and source records attributed to Remo Ruffini.

At least 109 records · Page 6Linked to original sources
arXiv2007

GRB970228 and a class of GRBs with an initial spikelike emission

(Shortened) The Swift and HETE-2 discovery of an afterglow associated possibly with short GRBs opened the new problematic of their nature and classification. This has been further enhanced by the GRB060614 observation and by a re-analysis of the BATSE catalog leading to the identification of a new GRB class with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission". We plan: a) to fit this new class of "hybrid" sources within our "canonical GRB" scenario, where all GRBs are generated by a "common engine" (i.e. the gravitational collapse to a black hole); b) to propose GRB970228 as the prototype of the such a class. We analyze BeppoSAX data on GRB970228 in the 40-700 keV and 2-26 keV energy bands within the "fireshell" model. We find that GRB970228 is a "canonical GRB", like e.g. GRB050315, with the main peculiarity of a particularly low CircumBurst Medium (CBM) average density n_{cbm}~10^{-3} #/cm^3. We also simulate the light curve corresponding to a rescaled CBM density profile with n_{cbm}=1 #/cm^3. From such a comparison it follows that the total time-integrated luminosity is a faithful indicator of the GRB nature, contrary to the peak luminosity which is merely a function of the CBM density. We call attention on discriminating the short GRBs between the "genuine" and the "fake" ones. The "genuine" ones are intrinsically short, with baryon loading B \la 10^{-5}, as stated in our original classification. The "fake" ones, characterized by an initial spikelike emission followed by an extended emission lasting tenths of seconds, have a baryon loading 10^{-4} \la B \leq 10^{-2}. They are observed as such only due to an underdense CBM consistent with a galactic halo environment which deflates the afterglow intensity.

astro-ph↗
arXiv2007

GRB060218 and GRBs associated with Supernovae Ib/c

We plan to fit the complete gamma- and X-ray light curves of the long duration GRB060218, including the prompt emission, in order to clarify the nature of the progenitors and the astrophysical scenario of the class of GRBs associated to SNe Ib/c. The initial total energy of the electron-positron plasma E_{e^\pm}^{tot}=2.32\times 10^{50} erg has a particularly low value similarly to the other GRBs associated with SNe. For the first time we observe a baryon loading B=10^{-2} which coincides with the upper limit for the dynamical stability of the fireshell. The effective CircumBurst Medium (CBM) density shows a radial dependence n_{cbm} \propto r^{-α} with 1.0<α<1.7 and monotonically decreases from 1 to 10^{-6} particles/cm^3. Such a behavior is interpreted as due to a fragmentation in the fireshell. Analogies with the fragmented density and filling factor characterizing Novae are outlined. The fit presented is particularly significant in view of the complete data set available for GRB060218 and of the fact that it fulfills the Amati relation. We fit GRB060218, usually considered as an X-Ray Flash (XRF), as a "canonical GRB" within our theoretical model. The smallest possible black hole, formed by the gravitational collapse of a neutron star in a binary system, is consistent with the especially low energetics of the class of GRBs associated with SNe Ib/c. We give the first evidence for a fragmentation in the fireshell. Such a fragmentation is crucial in explaining both the unusually large T_{90} and the consequently inferred abnormal low value of the CBM effective density.

astro-ph↗
arXiv2007

The Blackholic energy and the canonical Gamma-Ray Burst

We outline the main results of our GRB model, based on the three interpretation paradigms we proposed in July 2001, comparing and contrasting them with the ones in the current literature. Thanks to the observations by Swift and by VLT, this analysis points to a "canonical GRB" originating from markedly different astrophysical scenarios. The communality is that they are all emitted in the formation of a black hole with small or null angular momentum. The following sequence appears to be canonical: the vacuum polarization process creating an optically thick self accelerating electron-positron plasma; the engulfment of baryonic mass during the plasma expansion; the adiabatic expansion of the optically thick "fireshell" up to the transparency; the interaction of the remaining accelerated baryons with the interstellar medium (ISM). This leads to the canonical GRB composed of a proper GRB (P-GRB), emitted at the moment of transparency, followed by an extended afterglow. The parameters are the plasma total energy, the fireshell baryon loading and the ISM filamentary distribution around the source. In the limit of no baryon loading the total energy is radiated in the P-GRB. In this limit, the canonical GRBs explain as well the short GRBs.

astro-ph↗
arXiv2007

Equations of motion, initial and boundary conditions for GRB

We compare and contrast the different approaches to the optically thick adiabatic phase of GRB all the way to the transparency. Special attention is given to the role of the rate equation to be self consistently solved with the relativistic hydrodynamic equations. The works of Shemi and Piran (1990), Piran, Shemi and Narayan (1993), Meszaros, Laguna and Rees (1993) and Ruffini, Salmonson, Wilson and Xue (1999,2000) are compared and contrasted. The role of the baryonic loading in these three treatments is pointed out. Constraints on initial conditions for the fireball produced by electro-magnetic black hole are obtained.

astro-ph↗
arXiv2007

GRB 050315: A step toward the uniqueness of the overall GRB structure and the true nature of long GRBs

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, 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 confirms a clear hard-to-soft behavior encompassing, continuously, the "prompt emission" all the way to the latest phases of the afterglow. Consequences of the instrumental threshold on the definition of "short" and "long" GRBs are discussed.

astro-ph↗
arXiv2007

The role of GRB 031203 in clarifying the astrophysical GRB scenario

The luminosity and the spectral distribution of the afterglow of GRB 031203 have been presented within our theoretical framework, which envisages the GRB structure as composed by a proper-GRB, emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the "prompt emission" as due to external shocks. In addition to the GRB emission, there appears to be a prolonged soft X-Ray emission lasting for 10^6-10^7 seconds followed by an exponential decay. This additional source has been called by us URCA-3. It is urgent to establish if this component is related to the GRB or to the Supernova (SN). In this second case, there are two possibilities: either the interaction of the SN ejecta with the interstellar medium or, possibly, the cooling of a young neutron star formed in the SN 2003lw process. The analogies and the differences between this triptych GRB 031203 / SN 2003lw / URCA-3 and the corresponding ones GRB 980425 / SN 1998bw / URCA-1 and GRB 030329 / SN 2003dh / URCA-2, as well as GRB 060218 / SN 2006aj are discussed.

astro-ph↗
arXiv2007

Theoretical interpretation of GRB 011121

GRB011121 is analyzed as a prototype to understand the ``flares'' recently observed by Swift in the afterglow of many GRB sources. Detailed theoretical computation of the GRB011121 light curves in selected energy bands are presented and compared and contrasted with observational BeppoSAX data.

astro-ph↗
arXiv2007

GRB970228 as a prototype for short GRBs with afterglow

GRB970228 is analyzed as a prototype to understand the relative role of short GRBs and their associated afterglows, recently observed by Swift and HETE-II. Detailed theoretical computation of the GRB970228 light curves in selected energy bands are presented and compared with observational BeppoSAX data.

astro-ph↗
arXiv2007

Theoretical predictions of spectral evolution of short GRBs

We present the properties of spectrum of radiation emitted during gravitational collapse in which electromagnetic field strengths rise over the critical value for $e^+e^-$ pair creation. A drift from soft to a hard energy and a high energy cut off have been found; a comparison with a pure black body spectrum is outlined.

astro-ph↗
arXiv2006

Effective Lagrangian of QED

From the Euler-Heisenberg formula we calculate the exact real part of the one-loop effective Lagrangian of Quantum Electrodynamics in a constant electromagnetic field, and determine its strong-field limit.

hep-th↗
arXiv2006

Charged massive particle at rest in the field of a Reissner-Nordström black hole

The interaction of a Reissner-Nordström black hole and a charged massive particle is studied in the framework of perturbation theory. The particle backreaction is taken into account, studying the effect of general static perturbations of the hole following the approach of Zerilli. The solutions of the combined Einstein-Maxwell equations for both perturbed gravitational and electromagnetic fields at first order of the perturbation are exactly reconstructed by summing all multipoles, and are given explicit closed form expressions. The existence of a singularity-free solution of the Einstein-Maxwell system requires that the charge to mass ratios of the black hole and of the particle satisfy an equilibrium condition which is in general dependent on the separation between the two bodies. If the black hole is undercritically charged (i.e. its charge to mass ratio is less than one), the particle must be overcritically charged, in the sense that the particle must have a charge to mass ratio greater than one. If the charge to mass ratios of the black hole and of the particle are both equal to one (so that they are both critically charged, or "extreme"), the equilibrium can exist for any separation distance, and the solution we find coincides with the linearization in the present context of the well known Majumdar-Papapetrou solution for two extreme Reissner-Nordström black holes. In addition to these singularity-free solutions, we also analyze the corresponding solution for the problem of a massive particle at rest near a Schwarzschild black hole, exhibiting a strut singularity on the axis between the two bodies. The relations between our perturbative solutions and the corresponding exact two-body solutions belonging to the Weyl class are also discussed.

gr-qc↗
arXiv2006

Electrodynamics for Nuclear Matter in Bulk

A general approach to analyze the electrodynamics of nuclear matter in bulk is presented using the relativistic Thomas-Fermi equation generalizing to the case of $N \simeq (m_{\rm Planck}/m_n)^3$ nucleons of mass $m_n$ the approach well tested in very heavy nuclei ($Z \simeq 10^6$). Particular attention is given to implement the condition of charge neutrality globally on the entire configuration, versus the one usually adopted on a microscopic scale. As the limit $N \simeq (m_{\rm Planck}/m_n)^3$ is approached the penetration of electrons inside the core increases and a relatively small tail of electrons persists leading to a significant electron density outside the core. Within a region of $10^2$ electron Compton wavelength near the core surface electric fields close to the critical value for pair creation by vacuum polarization effect develop. These results can have important consequences on the understanding of physical process in neutron stars structures as well as on the initial conditions leading to the process of gravitational collapse to a black hole.

astro-ph↗
arXiv2006

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.

astro-ph↗
arXiv2006

Baryonic loading and e^+e^- rate equation in GRB sources

The expansion of the electron-positron plasma in the GRB phenomenon is compared and contrasted in the treatments of Meszaros, Laguna and Rees, of Shemi, Piran and Narayan, and of Ruffini et al. The role of the correct numerical integration of the hydrodynamical equations, as well as of the rate equation for the electron-positron plasma loaded with a baryonic mass, are outlined and confronted for crucial differences.

astro-ph↗
arXiv2006

Exact versus approximate beaming formulas in Gamma-Ray Burst afterglows

We present the exact analytic expressions to compute, assuming the emitted Gamma-Ray Burst (GRB) radiation is not spherically symmetric but is confined into a narrow jet, the value of the detector arrival time at which we start to "see" the sides of the jet, both in the fully radiative and adiabatic regimes. We obtain this result using our exact analytic expressions for the EQuiTemporal Surfaces (EQTSs) in GRB afterglows. We re-examine the validity of three different approximate formulas currently adopted for the adiabatic regime in the GRB literature. We also present an empirical fit of the numerical solutions of the exact equations, compared and contrasted with the three above approximate formulas. The extent of the differences is such as to require a reassessment on the existence and entity of beaming in the cases considered in the current literature, as well as on its consequences on the GRB energetics.

astro-ph↗
arXiv2006

GRB 050315: A step in the proof of the uniqueness of the overall GRB structure

Using the Swift data of GRB 050315, we progress in proving the uniqueness of our theoretically predicted Gamma-Ray Burst (GRB) structure as composed by a proper-GRB, emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the "prompt radiation" as due to external shocks. Detailed light curves for selected energy bands are theoretically fitted in the entire temporal region of the Swift observations ranging over 10^6 seconds.

astro-ph↗
arXiv2005

Theoretical interpretation of luminosity and spectral properties of GRB 031203

The X and gamma-ray observations of the source GRB 031203 by INTEGRAL are interpreted within our theoretical model. In addition to a complete space-time parametrization of the GRB, we specifically assume that the afterglow emission originates from a thermal spectrum in the co-moving frame of the expanding baryonic matter shell. By determining the two free parameters of the model and estimating the density and filamentary structure of the ISM, we reproduce the observed luminosity in the 20-200 keV energy band. As in previous sources, the prompt radiation is shown to coincide with the peak of the afterglow and the luminosity substructure are shown to originate in the filamentary structure of the ISM. We predict a clear hard-to-soft behavior in the instantaneous spectra. The time-integrated spectrum over 20 seconds observed by INTEGRAL is well fitted. Despite this source has been considered "unusual", it appears to us a normal low energetic GRB.

astro-ph↗