arXiv subjects

Yun-Peng Li

Publications and source records attributed to Yun-Peng Li.

6 recordsLinked to original sources

arXiv2026

Multi-wavelength Emission for a Post-merger Magnetar: The Magnetar-Driven Poynting Jet and Its Associated Pulsar Wind Nebula

A newborn, rapidly rotating magnetar may form in a binary neutron star merger and drive a Poynting-flux-dominated relativistic jet. As the jet propagates outward, a forward shock (FS) and a reverse shock (RS) are formed, inflating a pulsar wind nebula (PWN) between them. We present a systematic study of the emission from both the PWN and the jet, whose magnetic energy is subject to dissipation. By following the dynamics of the jet-ejecta-PWN system, we find that, in most cases, the RS is long-lived: it first lags behind the contact discontinuity and eventually coincides with both the contact discontinuity and the FS after the jet breakout into the external medium. As a result, the emission exhibits a characteristic temporal evolution. Depending on the optical depth, the emission is initially dominated by thermal radiation from the optically thick ejecta, then by a jet-powered X-ray plateau once the system becomes optically thin, and finally by synchrotron and inverse-Compton radiation from the PWN FS at late times. In particular, external inverse-Compton scattering of jet photons by the FS naturally produces a late-time GeV bump together with a substantial TeV component. Our model can simultaneously account for early thermal emission, X-ray plateaus, and late-time GeV excesses in merger-driven gamma-ray bursts, and also indicates that post-merger magnetar-driven PWNs are potential TeV photon sources.

astro-ph.HE↗

arXiv2026

L1 Regularization Paths in Linear Models by Parametric Gaussian Message Passing

The paper considers the computation of L1 regularization paths in a state space setting, which includes L1 regularized Kalman smoothing, linear SVM, LASSO, and more. The paper proposes two new algorithms, which are duals of each other; the first algorithm applies to L1 regularization of independent variables while the second applies to L1 regularization of dependent variables. The heart of the proposed algorithms is parametric Gaussian message passing (i.e., Kalman-type forward-backward recursions) in the pertinent factor graphs. The proposed methods are broadly applicable, they (usually) require only matrix multiplications, and their complexity can be competitive with prior methods in some cases.

cs.LG↗

arXiv2025

Jet precession in gamma-ray bursts: The roles of fallback accretion and disk dynamics

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.

astro-ph.HE↗

arXiv2025

Variabilities of Gamma-ray Bursts from the Dynamics of Fallback Material after Tidal Disruption

The gamma-ray burst (GRB) GRB 211211A and GRB 060614, believed to originate from the merger of compact objects, exhibit similarities to the jetted tidal disruption event (TDE) Sw J1644+57, by showing violent variabilities in the light-curve during the decay phase. Previous studies suggest that such fluctuations in TDE may arise from the fallback of tidal disrupted debris. In this paper, we introduce the fluctuations of the mass distribution ${\rm d}M/{\rm d}E$ for the debris ejected during the tidal disruption (with energy $E$) and study their impact on jet power. Turbulence induced by tidal force and the self-gravity of the debris may imprint variabilities in ${\rm d}M/{\rm d}E$ during fallback. We model these fluctuations with a power density spectrum $\propto f_{\rm E}^β$, where $f_{\rm E} = 1/E$ and $β$ is the power-law index. We find that the resulting light curve can preserve the fluctuation characteristics from ${\rm d}M/{\rm d}E$. In addition, the observed fluctuations in the light-curves can be reproduced for a given suitable $β$. Based on the observations, we find that the value of $β$ should be around $-1$.

astro-ph.HE↗

arXiv2025

Dual NUP Representations and Min-Maximization in Factor Graphs

Normals with unknown parameters (NUP) can be used to convert nontrivial model-based estimation problems into iterations of linear least-squares or Gaussian estimation problems. In this paper, we extend this approach by augmenting factor graphs with convex-dual variables and pertinent NUP representations. In particular, in a state space setting, we propose a new iterative forward-backward algorithm that is dual to a recently proposed backward-forward algorithm.

stat.ML↗

arXiv2024

Revisiting the Constraint on Equation of State of Neutron Star based on the Binary Neutron Star Mergers

The merger of neutron star (NS)-NS binary can form different production of the compact remnant, among which the supramassive NS (SMNS) could create an internal plateau and the followed steep decay marks the collapse of the SMNS. The proportion of SMNS and the corresponding collapse-time are often used to constrain the NS equation of state (EoS). This paper revisits this topic by considering the effect of an accretion disk on the compact remnant, which is not considered in previous works. Compared with previous works, the collapse-time distribution (peaks $\sim$100 s) of the SMNSs formed from NS-NS merger is almost unaffected by the initial surface magnetic ($B_{{\rm s},i}$) of NS, but the total energy output of the magnetic dipole radiation from the SMNSs depends on $B_{{\rm s},i}$ significantly. Coupling the constraints from the SMNS fraction, we exclude some EoSs and obtain three candidate EoSs, i.e., DD2, ENG, and MPA1. By comparing the distributions of the collapse-time and the luminosity of the internal plateau (in the short gamma-ray bursts) for those from observations with those obtained based on the three candidate EoSs, it is shown that only the EoS of ENG is favored. Our sample based on the ENG EOS and a mass distribution motivated by Galactic systems suggests that approximately $99\%$ of NS-NS mergers collapse to form a black hole within $10^7$s. This includes scenarios forming a BH promptly ($36.5\%$), a SMNS ($60.7\%$), or a stable NS that transitions into a BH or a SMNS following accretion ($2.1\%$). It also indicates that the remnants for GW170817 and GW190425, and the second object of GW190814 are more likely to be BHs.

astro-ph.HE↗