REVIEW
Jet precession in gamma-ray bursts: The roles of fallback accretion and disk dynamics
High Energy Astrophysical Phenomena · Submitted 27 Jun 2025 · 73 references
Pith's verdict: The two-phase precession period evolution is a genuinely new model result, but the two observational fits are too weak and the long-GRB branch rests on an untested envelope breakout assumption.
T0 · AI review
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Referee report
The paper
The paper claims
The gamma-ray burst jet precession period follows the accretion history: it drops during fallback and then rises nearly linearly as the disk spreads, explaining the widening pulse intervals seen in long and short bursts.
The reading
What carries the argument
The load-bearing object is the tilted thick accretion disk precessing almost as a rigid body under the Lense-Thirring torque, with period $T_{\rm prec}=2\pi\sin\psi\,J_d/N_d$, where $J_d=2\pi\int_{r_{\rm in}}^{r_{\rm out}}\Sigma(r,t)\Omega(r)r^3\,dr$ and $N_d=(4\pi G^2M_{\rm BH}^2a_{\rm BH}/c^3)\int_{r_{\rm in}}^{r_{\rm out}}\Sigma(r,t)\Omega(r)\,dr$. The disk's surface density $\Sigma$ is evolved from the fallback source term, while the black hole mass and spin evolve under accretion and Blandford-Znajek feedback; the precession angle $\psi(t)$ between the jet and a fixed observer then modulates a Gaussian structured jet, turning the period evolution into pulse intervals, widths, and amplitudes.
Extended reading notes
Core claim
On the paper's own terms, the discovery is that jet precession must be treated as a dynamical quantity tied to the same accretion that powers the burst. Combining a fallback rate with a diffusive disk equation and the Blandford-Znajek jet power, the authors evolve both the disk surface density and the black hole mass and spin, and feed the result into the rigid-body Lense-Thirring precession formula $T_{\rm prec} = 2\pi \sin\psi\, J_d/N_d$. The output is a two-phase period evolution: a rapid decrease while fallback dominates, then a near-linear increase, $T_{\rm prec}\propto t$, as the disk diffuses outward. They further show that high viscosity, thick disks, massive black holes, low spin, small fallback mass, and large fallback radius all lengthen the period or steepen its growth, while only the angles $\theta_p$, $\theta_c$, and $\theta_{\rm obs}$ control pulse amplitude. Fitting the resulting synthetic light curves to GRB 171126A and GRB 211129A is presented as evidence that precession explains their growing pulse intervals and widths, with the former attributed to a black hole-neutron star merger and the latter to a low-spin collapsar whose jet needs an additional power source.
Load-bearing premise
The long-GRB part of the paper assumes the jet keeps its precession pattern after breaking out of the progenitor envelope; if envelope interactions damp, misalign, or destroy the pattern, the fits to Type II bursts are unsupported.
Editorial extensions
If this is right
- The precession period of a GRB jet is a derived, time-dependent quantity, so fixed-period fits to multi-pulse light curves are at best a first approximation.
- Type I bursts whose pulse intervals widen are naturally explained as precessing jets from black hole-neutron star mergers, with GRB 171126A as a specific example.
- Type II bursts can show the same precession signature if the jet survives envelope breakout; GRB 211129A is fit with a low-spin black hole and may need neutrino-annihilation or Blandford-Payne power on top of the BZ mechanism.
- The predicted near-linear growth of $T_{\rm prec}$ smears out periodicity over a burst, which the authors link to why quasi-periodic oscillations are rare in Type I GRBs.
Reading between the lines
- If the linear-growth phase holds over many cycles, the precession phase advances quadratically, so bursts with many well-resolved pulses offer a cleaner test than the two fits presented; the paper itself does not perform this test.
- The black hole-neutron star interpretation of GRB 171126A implies that growing pulse intervals in short bursts could be used as a prompt-emission discriminator for compact-object mergers, connecting to gravitational-wave source classification.
- Because the breakout assumption is untested by simulation, a natural extension is to use general-relativistic magnetohydrodynamic simulations of jets crossing a stellar envelope to see whether and when the precession pattern survives; the long-burst conclusions depend on that answer.
Original abstract
The precession phenomenon of the jet in a gamma-ray burst (GRB) is a key probe of the physics of the central engine. Previous studies generally assumed a fixed precession period when analysing the temporal profiles in GRBs; however, the dynamic evolution of the fallback process and accretion disk can significantly affect the precession behaviour. In this work we present a jet precession model that incorporates the co-evolution of fallback accretion and the central black hole (BH). Our model demonstrates that the jet precession period initially decreases rapidly during the early fallback phase and subsequently increases nearly linearly as the disk evolves. We find that a higher accretion disk viscosity and a slower BH spin lead to longer precession periods and faster precession period growth rates, and that the geometric structure of the precession system modulates the pulse amplitude of the light curve. By fitting the model to observational data of GRBs with multi-pulse structures, we show that jet precession can naturally explain the increasing pulse intervals and broadened pulse widths observed in both long and short GRBs.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
The precession phenomenon of the jet in a gamma-ray burst (GRB) is a key probe of the physics of the central engine. Previous studies generally assumed a fixed precession period when analysing the temporal profiles in GRBs; however, the dynamic evolution of the fallback process and accretion disk can significantly affect the precession behaviour. In this work we present a jet precession model that incorporates the co-evolution of fallback accretion and the central black hole (BH). Our model demonstrates that the jet precession period initially decreases rapidly during the early fallback phase and subsequently increases nearly linearly as the disk evolves. We find that a higher accretion disk viscosity and a slower BH spin lead to longer precession periods and faster precession period growth rates, and that the geometric structure of the precession system modulates the pulse amplitude of the light curve. By fitting the model to observational data of GRBs with multi-pulse structures, we show that jet precession can naturally explain the increasing pulse intervals and broadened pulse widths observed in both long and short GRBs.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The precession phenomenon of the jet in a gamma-ray burst (GRB) is a key probe of the physics of the central engine. | background 1.00 | 0.05 | 0.03 | asserted 1.00 |
| s1 | Previous studies generally assumed a fixed precession period when analysing the temporal profiles in GRBs; however, the dynamic evolution of the fallback process and accretion disk can significantly affect the precession behaviour. | gap 0.84 | 0.05 | 0.06 | asserted 0.81 |
| s2 | In this work we present a jet precession model that incorporates the co-evolution of fallback accretion and the central black hole (BH). | contribution 0.85 | 0.94 | 0.07 | asserted 0.96 |
| s3 | Our model demonstrates that the jet precession period initially decreases rapidly during the early fallback phase and subsequently increases nearly linearly as the disk evolves. | result 1.00 | 0.96 | 0.35 | asserted 1.00 |
| s4 | We find that a higher accretion disk viscosity and a slower BH spin lead to longer precession periods and faster precession period growth rates, and that the geometric structure of the precession system modulates the pulse amplitude of the light curve. | result 1.00 | 0.95 | 0.18 | asserted 1.00 |
| s5 | By fitting the model to observational data of GRBs with multi-pulse structures, we show that jet precession can naturally explain the increasing pulse intervals and broadened pulse widths observed in both long and short GRBs. | result 0.80 | 0.96 | 0.68 | asserted 1.00 |
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Figures
Figures reproduced from arXiv:2506.22043 by the authors.
References
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Discussion
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