arXiv subjects

R. Ruffini

Publications and source records attributed to R. Ruffini.

At least 19 recordsLinked to original sources

arXiv2026

The angular structure of the GW170817 jet from prompt emission alone

We determine the angular structure of the GW170817 jet by the prompt emission alone, without afterglow fitting, circumburst density or microphysical parameters. We assume that GRB 090510 and GW170817 have outflows of the same kind, observed respectively on-axis and at the interferometric viewing angle of $20^\circ$. We support this assumption with independent gravitational-wave data showing compatible binary masses and radiated energies. We show that for an observer whose beaming cone is filled with outflow, the point-source Doppler scalings do not apply: $E_{\rm iso}=4\pi\epsilon(\theta_v)$, with $\epsilon$ the energy radiated per unit solid angle along the line of sight, while the peak energy follows $E_{\rm p,i}\propto\Gamma(\theta_v)$. We obtain $n={\rm d}\ln\epsilon/{\rm d}\ln\Gamma = 3.76\pm0.29$ from the ratio of the two bursts, with no free parameter and no assumed angle. This excludes four structures in common use at $4.7\sigma$ to $13\sigma$; three remain above $4\sigma$ across the full reported range of the peak energy of the GW170817 jet. Two prompt spectra fix no angular scale; supplying it with the core Lorentz factor of GRB 090510 and the viewing angle gives $\epsilon\propto\theta^{-7.4}$ outside a core of $2^\circ$--$5^\circ$, in agreement with the width inferred from $367$ short bursts, the outflow remaining relativistic at $\Gamma=33$ on the line of sight. The exponent exceeds what the Lorentz boost of a uniform comoving flow can produce, so the structure is intrinsic to the outflow and not a consequence of the boost. The same structure fixes the emission radius, which contributes $0.41$~s of the $1.74$~s delay between the gravitational-wave signal and the gamma-rays, the remainder being the launch and breakout of the jet, with no free parameters. We conclude that the faintness lies in the structure of the GW170817 jet, not in the de-beaming of a bright core.

astro-ph.HE↗

arXiv2026

GRB 220101A: a most energetic $10^{54}$ erg long GRB triggered by two supernovae 3.5 seconds apart

GRB 220101A is a long GRB, with a total energy exceeding $10^{54}$ erg with a redshift $z = 4.61$ and one of the largest ever high-quality multi-wavelength observational coverage, from a large number of space-based and ground-based telescopes. We interpret this source in a doubly Binary driven peta nova (BdP-N) model. The progenitor is composed of a massive CO core of $\sim 10\,M_\odot$, highly magnetized with $B \sim 10^{6}$ G, associated to a neutron star (NS) and a white dwarf (WD) with orbital periods from minutes to hours. The large GRB luminosity is explained by a sequence of 7 episodes: episode 1 is triggered by a new kind of pair supernova (HB) which originates from the collapse of the strongly magnetized CO core. Accretion of the HB supernova ejecta (the ejecta) onto the white dwarf companion triggers after 3.5 sec the episode 2: the second supernova emitting neutrinos and creating a new neutron star ($\nu$NS). The ejecta, interacting with the magnetosphere of the binary NS companion originate the episode 3: the Ultra relativistic Prompt Emission (UPE) emission by far the most energetic episode of this GRB, with the formation of a powerful jet normal to the plane of the GRB. Following the UPE energy loss, the accretion of the ejecta on the NS companion leads to the episode 4: the formation of a black hole (BH) of $2.3 \ M_\odot$ leading to the observed GeV afterglow emission. Further accretion of the ejecta spin up the $\nu$NS to a period of $1.3$ ms which gives origin to the episode 5: the birth of a pulsar. The interaction of this milli-second pulsar with the remnants lead to the Episode 6: the synchrotron emission observed in the X-ray, optical and radio, The episode 7 is a 56.7 ms pulsar, as observed $10^{10}$ s after the first burst in the crab nebula.

astro-ph.HE↗

arXiv2025

Selected topics on: 1) proposal of interpreting the Crab supernova with a GRB 2) progress in identifying the seven GRBs episodes 3) the role of Sagittarius A in identifying the dark matter component (the X fermion)

As the fiftieth anniversary of our common effort in the field of relativistic astrophysics is approaching, we offer a new look to some of our acquired knowledge in a more complete view, which evidence previous unnoticed connections. They are gaining due prominence in reaching a more complete picture evidencing the main results. We outline the history of GRB observations along with a summary of the contributions made by our group to develop the BdHN interpreting model. We show the seven Episodes characterizing the most powerful BdHNe I occurred to date: GRB 190114C and GRB 220101A. New inferences for the explanation of the highest energy radiation in the TeV are presented.

astro-ph.HE↗

arXiv2025

Large Language Models for Limited Noisy Data: A Gravitational Wave Identification Study

This work investigates whether large language models (LLMs) offer advantages over traditional neural networks for astronomical data processing, in regimes with non-Gaussian, non-stationary noise and limited labeled samples. Gravitational wave observations provide an suitable test case, using only 90 LIGO events, finetuned LLMs achieve 97.4\% accuracy for identifying signals. Further experiments show that, in contrast to traditional networks that rely on large simulated datasets, additional simulated samples do not improve LLM performance, while scaling studies reveal predictable gains with increasing model size and dataset size. These results indicate that LLMs can extract discriminative structure directly from observational data and provide an efficient assessment for gravitational wave identification. The same strategy may extend to other astronomical domains with similar noise properties, such as radio or pulsar observations.

astro-ph.IM↗

arXiv2025

Vacuum breakdown around a Kerr black hole surrounded by a magnetic field

We present the invariant characterization of the region where vacuum breakdown into electron-positron ($e^+e^-$) pairs occurs due to an overcritical electric field, the dyadoregion, in the case of a Kerr black hole (BH) in the presence of an external, asymptotically uniform test magnetic field aligned with the BH rotation axis, using the Wald solution. We calculate the dyadoregion morphology, the electromagnetic energy available to the pairs, the pair-creation rate, the pair number density, the average energy per pair, and the pair energy density and pressure. These results provide initial conditions for simulating the subsequent dynamics of the pair-produced plasma and astrophysical applications in the context of high-energy transients involving BHs in strong electromagnetic fields.

gr-qc↗

arXiv2025

Short GRB 090510: a magnetized neutron star binary merger leading to a black hole

We model the short gamma-ray bursts (GRB) 090510 as the product of a magnetized neutron star (NS) binary merger. Accounting for the NS critical mass constraint given by the mass of PSR J0952--0607, we infer that GRB 090510 was a highly-magnetized NS-NS merger that left as remnant a Kerr black hole (BH) of $2.4 M_\odot$ with a low-mass accretion disk. The gamma-ray precursor is powered by the magnetic energy released during the merger of the NSs. The prompt emission originates at the transparency of an ultra-relativistic $e^+e^-$ pair-plasma produced by the overcritical electric field induced by the rotating strong magnetic field around the merged object before it reaches the critical mass, the GeV emission by the extractable energy of the newborn BH, and the X-ray afterglow by accretion onto it. We derive the masses of the merging NSs, their magnetic fields, the BH mass, spin, and irreducible mass, the strength of the magnetic field, the disk mass, and obtain an estimate of the gravitational-wave emission during the merger phase preceding the prompt short GRB emission. The inferred parameters agree with up-to-date numerical relativity simulations, confirming that strong magnetic fields above $10^{14}$ G develop in NS-NS mergers and that mergers leading to a central BH remnant have low-mass disks of $\sim 10^{-2} M_\odot$. We also advance the possibility that quasi-period oscillations of tens of Hz of frequency due to Lense-Thirring precession of the matter surrounding the merged object before BH formation can explain the successive spikes following the prompt emission peak.

astro-ph.HE↗

arXiv2025

Evidence for Two SNe Type Triggering GRB 220101A: a Pair SN and a Rotating Magnetized Core Collapse SN

The traditional interpretation of gamma ray bursts (GRBs) as originating from a single black hole has been extended by the Binary Driven Hypernova (BdHN) model, in which a GRB arises from a binary system composed of a carbon oxygen (CO) core and a neutron star (NS) companion. This framework successfully reproduces the six canonical emission episodes observed in GRBs. Recent observations of energetic events, such as GRB 220101 and GRB 240825, suggest a more powerful variant involving a rapidly rotating, strongly magnetized CO core in a binary system with an NS. In this scenario, the collapse and possible fission of the CO core lead to the formation of a highly magnetized, rapidly rotating newborn neutron star. A pair instability supernova (pair SN) is triggered when rotation and magnetic effects drive the core to instability, influencing its collapse dynamics. This process results in a millisecond neutron star that later evolves into a pulsar. Concurrently, accretion of supernova ejecta onto the NS companion can induce its collapse into a black hole, powering high energy emission. This framework introduces two distinct classes of supernovae: (i) pair instability supernovae leaving no compact remnant, and (ii) magnetized, rotating core collapses producing pulsars. The model further incorporates the role of magnetic field amplification and magnetohydrodynamic processes, including the generation of overcritical fields and electron positron pair production. This represents a significant departure from earlier non rotating models and aligns with modern pair SN scenarios. BdHNe are characterized by seven physical episodes; notably, in pair SN cases, the final episode is not powered by radioactive nickel decay but by pulsar formation. These modifications are described within a leading order analytical framework.

astro-ph.HE↗

arXiv2024

The long-short GRB connection

Long and short gamma-ray bursts (GRBs) are thought to arise from different and unrelated astrophysical progenitors. The association of long GRBs with supernovae (SNe) and the difference in the distributions of galactocentric offsets of long and short GRBs within their host galaxies have often been considered strong evidence of their unrelated origins. Long GRBs have been thought to result from the collapse of single massive stars, while short GRBs come from mergers of compact object binaries. Our present study challenges this conventional view. We demonstrate that the observational properties, such as the association with SNe and the different galactic offsets, are naturally explained within the framework of the binary-driven hypernova model, suggesting an evolutionary connection between long and short GRBs.

astro-ph.HE↗

arXiv2024

Kerr black hole energy extraction, irreducible mass feedback, and the effect of captured particles charge

We analyze the extraction of the rotational energy of a Kerr black hole (BH) endowed with a test charge and surrounded by an external test magnetic field and ionized low-density matter. For a magnetic field parallel to the BH spin, electrons move outward (inward) and protons inward (outward) in a region around the BH poles (equator). For zero charge, the polar region comprises spherical polar angles $-60^\circ\lesssim \theta \lesssim 60^\circ$ and the equatorial region $60^\circ\lesssim \theta \lesssim 120^\circ$. The polar region shrinks for positive charge, and the equatorial region enlarges. For an isotropic particle density, we argue the BH could experience a cyclic behavior: starting from a zero charge, it accretes more polar protons than equatorial electrons, gaining net positive charge, energy, and angular momentum. Then, the shrinking(enlarging) of the polar(equatorial) region makes it accrete more equatorial electrons than polar protons, gaining net negative charge, energy, and angular momentum. In this phase, the BH rotational energy is extracted. The extraction process continues until the new enlargement of the polar region reverses the situation, and the cycle repeats. We show that this electrodynamical process produces a relatively limited increase of the BH irreducible mass compared to gravitational mechanisms like the Penrose process, hence being a more efficient and promising mechanism for extracting the BH rotational energy.

gr-qc↗

arXiv2024

Occurrence of gravitational collapse in the accreting neutron stars of binary-driven hypernovae

The binary-driven hypernova (BdHN) model proposes long gamma-ray bursts (GRBs) originate in binaries composed of a carbon-oxygen (CO) star and a neutron star (NS) companion. The CO core collapse generates a newborn NS and a supernova that triggers the GRB by accreting onto the NSs, rapidly transferring mass and angular momentum to them. This article aims to determine the conditions under which a black hole (BH) forms from NS collapse induced by the accretion and the impact on the GRB observational properties and taxonomy. We perform three-dimensional, smoothed-particle-hydrodynamics simulations of BdHNe using up-to-date NS nuclear equations of state (EOS), with and without hyperons, and calculate the structure evolution in full general relativity. We assess the binary parameters leading either NS in the binary to the critical mass for gravitational collapse into a BH and its occurrence time, $t_{\rm col}$. We include a non-zero angular momentum of the NSs and find that $t_{\rm col}$ ranges from a few tens of seconds to hours for decreasing NS initial angular momentum values. BdHNe I are the most compact (about five minutes orbital period), promptly form a BH and release $\gtrsim 10^{52}$ erg. They form NS-BH binaries with tens of kyr merger timescale by gravitational-wave emission. BdHNe II and III do not form BHs, release $\sim 10^{50}$-$10^{52}$ erg and $\lesssim 10^{50}$ erg. They form NS-NS binaries with a range of merger timescales larger than for NS-BH binaries. In some compact BdHNe II, either NS can become supramassive, i.e., above the critical mass of a non-rotating NS. Magnetic braking by a $10^{13}$ G field can delay BH formation, leading to BH-BH or NS-BH of tens of kyr merger timescale.

astro-ph.HE↗

arXiv2024

The role of the irreducible mass in repetitive Penrose energy extraction processes in a Kerr black hole

The concept of the irreducible mass ($M_{\rm irr}$) has led to the mass-energy ($M$) formula of a Kerr black hole (BH), in turn leading to its surface area $S=16\pi M_{\rm irr}^2$. This also allowed the coeval identification of the reversible and irreversible transformations, soon followed by the concepts of "extracted" and "extractable" energy. This new conceptual framework avoids inconsistencies recently evidenced in a repetitive Penrose process. We consider repetitive decays in the ergosphere of an initially extreme Kerr BH and show the processes are highly irreversible. For each decay, the particle that the BH captures causes an increase of the irreducible mass (so the BH horizon), much larger than the extracted energy. The energy extraction process stops {when the BH reaches a positive spin lower limit set by the process boundary conditions}. Thus, the reaching of a final non-rotating Schwarzschild BH state through this accretion process is impossible. We have assessed such processes for selected decay radii and incoming particle with rest mass $1\%$ of the BH initial mass $M_0$. For $r= 1.2 M$ and $1.9 M$, the sequence stops after $8$ and $34$ decays, respectively, at a spin $0.991$ and $0.857$, the energy extracted has been only $1.16\%$, and $0.42\%$, the extractable energy is reduced by $17\%$ and $56\%$, and the irreducible mass increases by $5\%$ and $22\%$, all values in units of $M_0$. These results show the highly nonlinear change of the BH parameters, dictated by the BH mass-energy formula, and that the BH rotational energy is mainly converted into irreducible mass. Thus, evaluating the irreducible mass increase in any energy extraction processes in the Kerr BH ergosphere is mandatory.

gr-qc↗

arXiv2024

Ten Supernova-rise in Binary Driven Gamma-ray Bursts

The observation of a gamma-ray burst (GRB) associated with a supernova (SN) coincides remarkably with the energy output from a binary system comprising a very massive carbon-oxygen (CO) core and an associated binary neutron star (NS) by the Binary-Driven Hypernova (BdHN) model. The dragging effect in the late evolution of such systems leads to co-rotation, with binary periods on the order of minutes, resulting in a very fast rotating core and a binary NS companion at a distance of $\sim 10^5$ km. Such a fast-rotating CO core, stripped of its hydrogen and helium, undergoes gravitational collapse and, within a fraction of seconds, leads to a supernova (SN) and a newly born, fast-spinning neutron star ($\nu$NS), we name the emergence of the SN and the $\nu$NS as the SN-rise and $\nu$NS-rise. Typically, the SN energies range from $10^{51}$ to $10^{53}$ erg. We address this issue by examining 10 cases of Type-I BdHNe, the most energetic ones, in which SN accretion onto the companion NS leads to the formation of a black hole (BH). In all ten cases, the energetics of the SN events are estimated, ranging between $0.18$ and $12 \times 10^{52}$ erg. Additionally, in all 8 sources at redshift $z$ closer than $4.61$, a clear thermal blackbody component has been identified, with temperatures between $6.2$ and $39.99$ keV, as a possible signature of pair-driven SN. The triggering of the X-ray afterglow induced by the $\nu$NS-rise are identified in three cases at high redshift where early X-ray observations are achievable, benefits from the interplay of cosmological effects.

astro-ph.HE↗

arXiv2024

On the formation of compact-object binaries from binary-driven hypernovae

We present smoothed-particle-hydrodynamics (SPH) simulations of the binary-driven hypernova (BdHN) scenario of long gamma-ray bursts (GRBs), focusing on the binary stability during the supernova (SN) explosion. The BdHN progenitor is a binary comprised of a carbon-oxygen (CO) star and a neutron star (NS) companion. The core collapse of the CO leads to an SN explosion and a newborn NS ($\nu$NS) at its center. Ejected material accretes onto the NS and the $\nu$NS. BdHNe of type I have compact orbits of a few minutes, the NS reaches the critical mass, forming a black hole (BH), and the energy release is $\gtrsim 10^{52}$ erg. BdHNe II have longer periods of tens of minutes to hours; the NS becomes more massive, remains stable, and the system releases $\sim 10^{50}$-$10^{52}$ erg. BdHN III have longer periods, even days, where the accretion is negligible, and the energy released is $\lesssim 10^{50}$ erg. We assess whether the system remains gravitationally bound after the SN explosion, leading to an NS-BH in BdHN I, an NS-NS in BdHN II and III, or if the SN explosion disrupts the system. The existence of bound systems predicts an evolutionary connection between the long and short GRB populations. We determine the binary parameters for which the binary remains bound after the BdHN event. For these binaries, we derive fitting formulas of the numerical results for the main parameters, e.g., the mass loss, the SN explosion energy, orbital period, eccentricity, center-of-mass velocity, and the relation between the initial and final binary parameters, which are useful for outlined astrophysical applications.

astro-ph.HE↗

arXiv2023

Baryon-induced collapse of dark matter cores into supermassive black holes

Non-linear structure formation for fermionic dark matter particles leads to dark matter density profiles with a degenerate compact core surrounded by a diluted halo. For a given fermion mass, the core has a critical mass that collapses into a supermassive black hole (SMBH). Galactic dynamics constraints suggest a $\sim 100$ keV/$c^2$ fermion, which leads to $\sim 10^7 M_\odot$ critical core mass. Here, we show that baryonic (ordinary) matter accretion drives an initially stable dark matter core to SMBH formation and determine the accreted mass threshold that induces it. Baryonic gas density $\rho_b$ and velocity $v_b$ inferred from cosmological hydro-simulations and observations produce sub-Eddington accretion rates triggering the baryon-induced collapse in less than a Gyr. This process produces active galactic nuclei in galaxy mergers and the high-redshift Universe. For TXS 2116-077, merging with a nearby galaxy, the observed $3\times 10^7 M_\odot$ SMBH, for $Q_b = \rho_b/v_b^3 = 0.125 M_\odot/(100 \text{km/s pc})^3$, forms in $\approx 0.6$ Gyr, consistent with the $0.5$-$2$ Gyr merger timescale and younger jet. For the farthest central SMBH detected by the \textit{Chandra} X-ray satellite in the $z=10.3$ UHZ1 galaxy observed by the James Webb Space Telescope (\textit{JWST}), the mechanism leads to a $4\times 10^7 M_\odot$ SMBH in $87$-$187$ Myr, starting the accretion at $z=12$-$15$. The baryon-induced collapse can also explain the $\approx 10^7$-$10^8 M_\odot$ SMBHs revealed by the JWST at $z\approx 4$-$6$. After its formation, the SMBH can grow to a few $10^9 M_\odot$ in timescales shorter than a Gyr via sub-Eddington baryonic mass accretion.

astro-ph.GA↗

arXiv2023

Neutron star binaries produced by binary-driven hypernovae, their mergers, and the link between long and short GRBs

The binary-driven hypernova (BdHN) model explains long gamma-ray bursts (GRBs) associated with supernovae (SNe) Ic through physical episodes that occur in a binary composed of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit. The CO core collapse triggers the cataclysmic event, originating the SN and a newborn NS (hereafter $\nu$NS) at its center. The $\nu$NS and the NS accrete SN matter. BdHNe are classified based on the NS companion fate and the GRB energetics, mainly determined by the orbital period. In BdHNe I, the orbital period is of a few minutes, so the accretion causes the NS to collapse into a Kerr black hole (BH), explaining GRBs of energies $>10^{52}$ erg. BdHN II, with longer periods of tens of minutes, yields a more massive but stable NS, accounting for GRBs of $10^{50}$--$10^{52}$ erg. BdHNe III have still longer orbital periods (e.g., hours), so the NS companion has a negligible role, which explains GRBs with a lower energy release of $<10^{50}$ erg. BdHN I and II might remain bound after the SN, so they could form NS-BH and binary NS (BNS), respectively. In BdHN III, the SN likely disrupts the system. We perform numerical simulations of BdHN II to compute the characteristic parameters of the BNS left by them, their mergers, and the associated short GRBs. We obtain the mass of the central remnant, whether it is likely to be a massive NS or a BH, the conditions for disk formation and its mass, and the event's energy release. The role of the NS nuclear equation of state is outlined.

astro-ph.HE↗

arXiv2023

On the occurrence of stellar fission in binary-driven hypernovae

The binary-driven hypernova (BdHN) model address long gamma-ray bursts (GRBs) associated with type Ic supernovae (SNe) through a series of physical episodes that occur in a binary composed of a carbon-oxygen (CO) star (of mass about 10 solar mass) and a neutron star (NS) companion (of mass about 2 solar mass) in a compact orbit. The SN explosion of the CO star triggers sequence of seven events. The BdHN model has followed the traditional picture of the SN from the CO iron's core collapse. However, the lack of a solution to the problem of producing successful SNe leaves room for alternative scenarios. We here show that tidal synchronization of the CO-NS binary can lead the CO star to critical conditions for fission, hence splitting into two stellar remnants, e.g., about 8.5 solar mass + 1.5 solar mass. We give specific examples of the properties of the products for various orbital periods relevant to BdHNe. The astrophysical consequences of this scenario are outlined.

astro-ph.HE↗

arXiv2023

Probing electromagnetic-gravitational wave emission coincidence in type I binary-driven hypernova family of long GRBs at very-high redshift

The repointing time of the XRT instrument on the Neil Gehrels Swift Observatory satellite has posed challenges in observing and studying the early X-ray emissions within $\approx40$ s after a gamma-ray burst (GRB) trigger. To address this issue, we adopt a novel approach that capitalizes on the cosmological time dilation in GRBs with redshifts ranging from $3$ to $9$. Applying this strategy to Swift/XRT data, we investigate the earliest X-ray emissions of $368$ GRBs from the Swift catalog, including short and long GRBs. We compare the time delay between the GRB trigger and the initial Swift/XRT observation, measured in the GRB observer frame (OTD) and the cosmological rest-frame (RTD). This technique is here used in the analysis of GRB 090423 at $z=8.233$ (RTD $\sim8.2$ s), GRB 090429B at $z\approx9.4$ (RTD $\sim10.1$ s), and GRB 220101A at $z=4.61$ (RTD $\sim14.4$ s). The cosmological time dilation enables us to observe the very early X-ray afterglow emission in these three GRBs. We thus validate the observation of the collapse of the carbon-oxygen (CO) core and the coeval newborn neutron star ($\nu$NS) formation triggering the GRB event in the binary-driven hypernova (BdHN) scenario. We also evidence the $\nu$NS spin-up due to supernova ejecta fallback and its subsequent slowing down due to the X-optical-radio synchrotron afterglow emission. A brief gravitational wave signal may separate the two stages due to a fast-spinning $\nu$NS triaxial-to-axisymmetric transition. We also analyze the long GRB redshift distribution for the different BdHN types and infer that BdHNe II and III may originate the NS binary progenitors of short GRBs.

astro-ph.HE↗

arXiv2023

On the growth of supermassive black holes formed from the gravitational collapse of fermionic dark matter cores

Observations support the idea that supermassive black holes (SMBHs) power the emission at the center of active galaxies. However, contrary to stellar-mass BHs, there is a poor understanding of their origin and physical formation channel. In this article, we propose a new process of SMBH formation in the early Universe that is not associated with baryonic matter (massive stars) or primordial cosmology. In this novel approach, SMBH seeds originate from the gravitational collapse of fermionic dense dark matter (DM) cores that arise at the center of DM halos as they form. We show that such a DM formation channel can occur before star formation, leading to heavier BH seeds than standard baryonic channels. The SMBH seeds subsequently grow by accretion. We compute the evolution of the mass and angular momentum of the BH using a geodesic general relativistic disk accretion model. We show that these SMBH seeds grow to $\sim 10^9$-$10^{10} M_\odot$ in the first Gyr of the lifetime of the Universe without invoking unrealistic (or fine-tuned) accretion rates.

astro-ph.CO↗