Binary Driven Hypernova: A Multi-Episode GRB Model

• BdHN is a framework describing long gamma-ray bursts arising from tight carbon–oxygen core and neutron star binaries undergoing hypercritical accretion, sometimes leading to neutron star collapse into a black hole.
• The model features a multi-episode emission sequence—from initial supernova and νNS rise to BH electrodynamics and synchronized afterglow—that clarifies distinct prompt and late-time signals.
• BdHN subclasses (I, II, III) are classified by orbital period and accretion strength, influencing GRB energetics, remnant formation, and gravitational wave predictions.

Binary Driven Hypernova (BdHN) denotes a class of long gamma-ray bursts (GRBs) interpreted as the outcome of a tight binary composed of a carbon–oxygen core at the end of nuclear evolution and a neutron-star companion. In the BdHN framework developed by Ruffini, Rueda, Becerra, and collaborators, the CO core collapses, forms a newborn neutron star ($\nu$NS), and launches a Type Ic supernova; the supernova ejecta then interact with the companion NS, driving hypercritical accretion, spinning up both compact objects, and, in the most compact systems, inducing the collapse of the companion NS into a black hole. The term therefore refers simultaneously to a specific binary progenitor, a hyper-energetic SN–GRB phenomenon, and a multi-episode, multi-wavelength emission sequence (Bianco et al., 2023).

1. Progenitor system and subclass taxonomy

The BdHN scenario originated in the induced gravitational collapse literature, where the most energetic long GRBs associated with Type Ib/c supernovae were attributed to a tight binary consisting of an evolved FeCO or CO core and a neutron-star companion rather than to the collapse of a single star. In this picture, the “in” state is a CO-core–NS binary and the “out” state depends mainly on orbital period, accretion history, and the critical mass of the NS companion (Ruffini et al., 2014).

Appendix A of the high-redshift BdHN study and later subclass papers identify three main families sharing the same basic progenitor but differing in compactness and outcome. The orbital period controls the ejecta density at the NS location, the accretion rate, and therefore whether the companion remains an NS or collapses to a BH (Bianco et al., 2023).

Subclass	Orbital scale and energetics	Outcome and representative events
BdHN I	$\approx 5$ min; $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$	NS companion collapses to a BH; GRB 130427A, 180720B, 190114C
BdHN II	$\approx 20$–$40$ min; $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$	No BH formation; final $\nu$NS + NS or MNS system; GRB 190829A, GRB 180728A
BdHN III	hours; $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$	Accretion onto the companion is negligible; GRB 171205A

BdHN II is described in complementary language in the detailed analyses of GRB 190829A and GRB 180728A: orbital periods of tens of minutes, hypercritical accretion onto the companion NS that does not reach the critical mass, and prompt luminosities consistent with accretion power of order $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$ (Wang et al., 2022). For BdHN III, the orbital period may extend to hours or even days, so the companion becomes observationally irrelevant and the event is effectively powered by fallback onto the $\nu$NS born in the CO-core collapse (Wang et al., 2022).

A recurrent point in the taxonomy is that the optical SN is not tightly correlated with the GRB energy. The comparison of GRB 130427A/SN 2013cq and GRB 180728A/SN 2018fip emphasizes that both events show similar broad-lined Type Ic spectra although their GRB energetics differ by $\approx 5$0, a result used to argue that the SN acts as the catalyst for the accretion-driven GRB rather than as the direct determinant of the GRB energy budget (Wang et al., 2018).

2. Multi-episode dynamical sequence

Later BdHN I work resolves the source into a seven-episode sequence. Episode I is the SN-rise: collapse of the CO core, formation of the $\approx 5$1NS, and launch of a Type Ic SN. In the high-redshift analysis, the SN-rise is an X–$\approx 5$2-ray transient lasting $\approx 5$3–4 s in the rest frame, with inferred energies $\approx 5$4 for GRB 220101A, $\approx 5$5 for GRB 090423, and $\approx 5$6 for GRB 090429B (Bianco et al., 2023).

Episode II is the $\approx 5$7NS-rise and NS-rise, driven by accretion of supernova ejecta onto the central $\approx 5$8NS and onto the NS companion. This phase is crucial because it is the first direct electromagnetic manifestation of the $\approx 5$9NS, and because in BdHN I the companion NS reaches the critical mass and collapses to a BH at the end of the episode. The early-XRT analyses interpret the first rising X-ray component immediately after the SN-rise as precisely this fallback-driven spin-up phase of the $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$0NS (Bianco et al., 2023).

Episode III is the BH-rise or ultra-relativistic prompt emission (UPE). In BdHN I the newly formed BH, threaded by a strong magnetic field inherited from the NS and accretion flow, generates an overcritical electric field, creates an $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$1 pair plasma, and powers the prompt MeV emission. Episode IV is the GeV emission, attributed to continued extraction of BH rotational energy in less baryon-loaded directions. Episode V consists of “BH echoes,” including cavity emission and X-ray flares produced by interaction of the pair plasma with the cavity and surrounding ejecta (Moradi et al., 2021).

GRB 180720B provides a concrete episode decomposition in the first $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$2 s rest frame: SN-rise, UPE, cavity emission, hard X-ray flare, and soft X-ray flare. In that source the GeV luminosity decays as a power law and is attributed to BH electrodynamics, while the X-ray afterglow is attributed to the $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$3NS (Moradi et al., 2021). For GRB 190114C, the cavity itself was modeled explicitly: hypercritical accretion and collapse of the NS companion carve a low-density cavity of radius $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$4, part of the $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$5 plasma is reflected off the cavity wall, and the resulting featureless emission between $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$6 and $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$7 s is identified with a distinct BdHN I episode (Ruffini et al., 2019).

The original high-redshift BdHN paper had described a four-episode structure in the induced gravitational collapse language: Episode 1 as SN explosion and hypercritical accretion, Episode 2 as prompt GRB from NS collapse to BH, Episode 3 as the long-lived X-ray component, and Episode 4 as the optical SN bump (Ruffini et al., 2014). The later seven-episode sequence is therefore an extension and refinement, not a replacement, of the earlier phenomenology.

3. Accretion, $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$8NS spin evolution, and afterglow physics

The $E_{\rm iso}\sim 10^{52}-10^{54}\,\mathrm{erg}$9NS is the key long-lived engine in the BdHN framework. Matter fallback and binary-driven ejecta dynamics provide the early spin-up torque, while magnetic braking and synchrotron-powered ejecta emission govern the later afterglow. In the compact-binary simulations of the first minutes of a BdHN, the total torque is written as

$\approx 20$0

with accretion torque

$\approx 20$1

where $\approx 20$2 is the specific angular momentum at the ISCO or stellar surface and $\approx 20$3 is an angular-momentum transfer efficiency. Those simulations show a distinctive result: the rotational power of the $\approx 20$4NS has a unique double-peak structure, while that of the NS companion has a single dominant peak (Becerra et al., 2022).

The physical origin of the $\approx 20$5NS double peak is the two-component fallback history. There is an early fallback component analogous to a single-star core collapse, followed by a binary-enhanced second peak caused by the gravitational perturbation of the NS companion and by flow redirection from the thick disk around it. By contrast, the NS companion accretion rate shows one main peak associated with the densest ejecta crossing the companion’s capture region (Becerra et al., 2022). This result is used in the BdHN interpretation of double-pulse prompt emission in nearby events such as GRB 190829A, where one pulse is associated with accretion onto the companion NS and the other with the binary-enhanced second fallback peak onto the $\approx 20$6NS (Wang et al., 2022).

The early and late luminosity scalings are described in the high-redshift BdHN I analysis by the standard fallback and dipole relations

$\approx 20$7

together with

$\approx 20$8

At early times $\approx 20$9, so the $40$0NS spins up and the electromagnetic luminosity rises; once fallback wanes, spin-down dominates and the light curve becomes a power law with $40$1 typically in the range $40$2 to $40$3 (Bianco et al., 2023).

The nearby BdHN II case GRB 190829A provides the most explicit afterglow model. There the ejecta radius evolves as

$40$4

with magnetic field

$40$5

and electron distribution $40$6 governed by a kinetic equation with synchrotron and adiabatic losses. The energy injection law is parameterized as

$40$7

and the synchrotron luminosity then becomes a power law both in time and in frequency. An important consequence is that X-ray, optical, and radio afterglows must decay with the same temporal slope and fixed flux ratios when they lie in the same cooling regime, a feature reported for GRB 190829A after the early complex phase (Wang et al., 2022).

The same source is modeled with a combined dipole+quadrupole pulsar torque,

$40$8

where $40$9 is the quadrupole-to-dipole strength ratio. The fit gives $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$0 ms, $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$1 G, $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$2, $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$3, $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$4 s, $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$5, and $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$6 (Wang et al., 2022).

At the opposite end of the taxonomy, BdHN III is exemplified by GRB 171205A. There the $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$7NS is assumed to be born non-rotating and spun up by fallback accretion to a period of $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$8 ms; the modest rotational reservoir then powers a weak synchrotron afterglow, while the optical SN from radioactive nickel decay outshines the non-thermal optical component. The same modeling leads to the inference that the SN explosion had to occur at most $E_{\rm iso}\sim 10^{50}-10^{52}\,\mathrm{erg}$9 h before the GRB trigger (Wang et al., 2022).

4. Representative events across the BdHN families

The observational literature on BdHNe is organized around a set of archetypal bursts. For BdHN I, GRB 130427A, GRB 180720B, and GRB 190114C are the most frequently used prototypes. GRB 180720B, at $\nu$0 and $\nu$1 erg, is interpreted as a CO-core–NS system with $\nu$2 min, BH formation, long-lived GeV emission from the BH inner engine, and X-ray afterglow from the $\nu$3NS. Its H.E.S.S. 100–440 GeV emission, with total energy $\nu$4 erg and duration $\nu$5 s, is attributed to a glitch in the spinning $\nu$6NS during its slowing-down phase (Moradi et al., 2021).

For GRB 130427A, the GeV emission is treated as the prototype of the BdHN I “inner engine.” The BH is modeled as a Kerr BH immersed in a uniform magnetic field $\nu$7, aligned with the spin axis and surrounded by plasma of density $\nu$8. Matching the GeV energetics and transparency gives $\nu$9, $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$0, and $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$1 G; electrons accelerated near the horizon can reach $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$2 eV along the polar axis and produce GeV–TeV synchrotron emission at nonzero pitch angle (Ruffini et al., 2018).

GRB 190114C extends this BH-electrodynamic program. In the corresponding inner-engine treatment, a Kerr BH of mass $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$3, spin $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$4, and magnetic field $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$5 G is inferred from the GeV luminosity, the transparency requirement, and the synchrotron-radiation timescale. The same work argues for a broad GeV emission cone with semi-aperture angle of approximately $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$6 with respect to the BH rotation axis (Moradi et al., 2019).

BdHN II is anchored by GRB 190829A and GRB 180728A. GRB 190829A, at $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$7, is interpreted as a binary late-evolution event in which the prompt double pulse arises from accretion onto the companion NS and from the second peak of $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$8NS fallback accretion; the one-zone synchrotron model reproduces the radio, optical, and X-ray afterglows, while the H.E.S.S. TeV component is found to be incompatible with synchrotron self-Compton in that same zone and is therefore assigned to a different process or zone linked to the $E_{\rm iso}\lesssim 10^{50}\,\mathrm{erg}$9NS (Wang et al., 2022). GRB 180728A provides a cleaner prompt-phase BdHN II diagnostic: a precursor interpreted as SN shock breakout, a main spike interpreted as the onset of hypercritical accretion when the SN ejecta reach the NS companion, and a thermal blackbody component attributed to a convective-instability bubble in the accretion flow. The inferred binary separation is $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$0, and the $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$1NS initial spin inferred from the afterglow is $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$2 ms (Wang et al., 2018).

BdHN III is exemplified by GRB 171205A/SN 2017iuk, a low-luminosity, long-duration GRB associated with a broad-line Type Ic hypernova. The wide binary separation makes the companion effectively irrelevant for observables; fallback onto the $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$3NS powers the prompt emission, and the $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$4NS later spins down from a period of $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$5 ms, powering a weak synchrotron afterglow. The low rotational energy explains the low-luminosity character and the dominance of the SN optical light over the optical synchrotron (Wang et al., 2022).

5. High-redshift diagnostics, gravitational waves, and population structure

A distinctive methodological development in BdHN research is the use of cosmological time dilation to access early X-ray rest-frame times despite the $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$6 s repointing delay of Swift/XRT. Defining the observer-frame delay as OTD and the rest-frame delay as

$10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$7

the high-redshift study of 368 Swift GRBs showed that while the minimum OTD is $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$8 s, RTD can reach $10^{48}-10^{49}\,\mathrm{erg\,s^{-1}}$9–10 s at $\nu$0–10. This made it possible to analyze GRB 220101A ($\nu$1, RTD $\nu$2 s), GRB 090423 ($\nu$3, RTD $\nu$4 s), and GRB 090429B ($\nu$5, RTD $\nu$6 s) in the time interval immediately after the SN-rise, and to identify directly the $\nu$7NS-rise followed by power-law afterglow decay (Bianco et al., 2023).

For those three BdHN I candidates, the decaying XRT component is fitted as

$\nu$8

with $\nu$9 for GRB 220101A, $\approx 5$00 for GRB 090423, and $\approx 5$01 for GRB 090429B. The same work interprets this as direct evidence, at $\approx 5$02–9.4, for CO-core collapse and $\approx 5$03NS formation triggering the GRB, early $\approx 5$04NS spin-up by fallback, and subsequent $\approx 5$05NS spin-down powering the afterglow (Bianco et al., 2023).

GRB 090423 has also served as an early test case for BdHN scaling laws. By comparing it with the prototype BdHN GRB 090618 in the common rest frame, the induced gravitational collapse study identified the overlap of the late X-ray Episode 3 power law and proposed this late X-ray component as a possible standard candle. The same paper argued that the presence of a BdHN at $\approx 5$06 implies that SN events leading to NS formation already occurred at 650 Myr after the Big Bang and may have originated from $\approx 5$07–$\approx 5$08 binaries, probing Population II stars after the completion and possible disappearance of Population III stars (Ruffini et al., 2014).

The $\approx 5$09NS also provides a specific gravitational-wave prediction. In the Jacobi–Maclaurin treatment of GRB 180720B and GRB 190114C, the observed $\approx 5$10NS-rise and afterglow are powered by the release of rotational energy of a Maclaurin spheroid beginning at the bifurcation point to the Jacobi sequence. The implication is that the $\approx 5$11NS was initially triaxial, radiated copiously in gravitational waves, and transitioned into an axisymmetric configuration before the observed $\approx 5$12NS-rise. Using

$\approx 5$13

the paper estimates $\approx 5$14, a duration $\approx 5$15 s, and a characteristic strain

$\approx 5$16

at frequencies $\approx 5$17–4 kHz (Rueda et al., 2022). The high-redshift BdHN I paper expresses a related idea more phenomenologically, as a brief GW signal associated with a fast-spinning $\approx 5$18NS triaxial-to-axisymmetric transition separating the $\approx 5$19NS-rise from the settled power-law afterglow (Bianco et al., 2023).

BdHN studies also extract population-level consequences. In the 368-GRB Swift sample with measured redshift and XRT delay, the long-GRB redshift distribution is double-peaked, with maxima around $\approx 5$20–1.5 and $\approx 5$21–2.5. Restricting to a pre-2019 subsample, 216 sources are identified as BdHN I, 64 as BdHN II/III candidates, and 21 as short GRBs. The redshift distributions of BdHN I and BdHN II/III are clearly different ($\approx 5$22 in a K–S test), while BdHN II/III vs short GRBs gives $\approx 5$23, interpreted as not significantly different. The inference proposed is that BdHN II and III leave behind bound compact binaries that later merge and produce short GRBs (Bianco et al., 2023).

6. Compact remnants, model comparisons, and outstanding issues

Three-dimensional SPH simulations place the BdHN scenario on a dynamical basis. The 2024 remnant-formation study simulates CO-core–NS binaries through the SN explosion and asks whether the system remains bound. It finds that BdHNe I have compact orbits of a few minutes, the NS reaches the critical mass and forms a BH, and the energy release is $\approx 5$24 erg; BdHNe II have longer periods of tens of minutes to hours, the NS remains stable, and the energy release is $\approx 5$25–$\approx 5$26 erg; BdHN III have longer periods, even days, with negligible accretion and energy release $\approx 5$27 erg. For bound systems, the post-SN remnant is NS–BH in BdHN I and NS–NS in BdHN II and III (Becerra et al., 2024).

That work also shows that the classical instantaneous-mass-loss criterion is inadequate for BdHNe: many systems remain bound even when more than half the total mass is lost, because the mass loss is not instantaneous and because accretion onto the compact objects reduces the effective loss and transfers momentum. The final energy can be fit as a quadratic in

$\approx 5$28

and the maximum initial orbital period for which the binary remains bound is fit as a function of $\approx 5$29 (Becerra et al., 2024). The companion paper on accretion-induced collapse then adds full general-relativistic NS-structure evolution with modern EOSs and finds that in compact BdHNe I the collapse time $\approx 5$30 ranges from a few tens of seconds to hours for decreasing NS initial angular momentum values. It also identifies compact BdHNe II in which either NS can become supramassive, so that magnetic braking by a $\approx 5$31 G field can trigger delayed BH formation and ultimately produce NS–BH or BH–BH binaries with tens-of-kyr GW merger timescales (Becerra et al., 2024).

These remnant studies reinforce the proposed evolutionary link between the long- and short-GRB populations. BdHN I systems form NS–BH binaries with merger timescales of tens of kyr by gravitational-wave emission, whereas BdHN II and III form NS–NS binaries with a broader distribution of merger timescales (Becerra et al., 2024). A plausible implication is that the subclass taxonomy is not only an electromagnetic classification but also a compact-remnant classification.

Relative to competing GRB models, the BdHN framework differs most sharply in four respects. First, it replaces the single-star collapsar progenitor with a CO-core–NS binary. Second, it assigns distinct physical engines to distinct episodes: $\approx 5$32NS formation and fallback, NS-collapse–induced BH formation, BH electrodynamics, cavity echoes, and $\approx 5$33NS-powered afterglow (Bianco et al., 2023). Third, it makes the $\approx 5$34NS central to both the early X-ray rise and the long-term X-ray/optical/radio afterglow, rather than treating the afterglow solely as an external forward shock. Fourth, in several detailed cases it treats very-high-energy emission as incompatible with a one-zone synchrotron or synchrotron-self-Compton scenario and instead ties it to distinct zones or to $\approx 5$35NS activity (Wang et al., 2022).

The framework is nevertheless accompanied by explicit caveats. The high-redshift BdHN I analysis models only three events in detail and notes RTD-based selection biases, the absence of GW detections, and degeneracy with external-shock power-law decays (Bianco et al., 2023). The GRB 190829A afterglow study uses a one-zone synchrotron model with spherical symmetry and leaves the VHE component unexplained within that same zone (Wang et al., 2022). The first-minutes SPH study computes large-scale hydrodynamics in Newtonian gravity and parameterizes the angular momentum of accreted matter through the ISCO rather than extracting it directly from the SPH flow (Becerra et al., 2022). The accretion-induced collapse study includes full general relativity for the NS structure but still treats the large-scale ejecta hydrodynamics in SPH and leaves magnetic-field burial and detailed neutrino transport outside the scope of the calculation (Becerra et al., 2024).

Future tests are correspondingly specific. Proposed X-ray missions such as THESEUS and HERMES are invoked as ways to observe Episodes I and II without relying on cosmological time dilation, while Einstein Telescope and Cosmic Explorer are invoked as the natural facilities for testing the predicted brief, kHz-band $\approx 5$36NS gravitational-wave signal and the compact-remnant merger channel (Bianco et al., 2023). Within the present literature, Binary Driven Hypernovae therefore constitute a tightly linked program in which progenitor binary evolution, hypercritical accretion, NS and BH criticality, multi-episode GRB phenomenology, and compact-binary remnants are treated as different manifestations of the same physical system.