arXiv subjects

Boris Betancourt-Kamenetskaia

Publications and source records attributed to Boris Betancourt-Kamenetskaia.

4 recordsLinked to original sources

arXiv2026

Deep Newtonian Afterglows: Theoretical Light Curves for Quasi-spherical Outflows

We investigate late-time gamma-ray burst (GRB) afterglows produced by quasi-spherical outflows propagating into a stratified circumburst medium during the deep Newtonian phase. Sub-relativistic ejecta generated in compact binary mergers or core-collapse explosions naturally develop velocity structures, while additional energy injection from a long-lived central engine, through spin-down luminosity and/or fallback accretion, can substantially modify the afterglow evolution. We develop an analytical framework for synchrotron emission from decelerated ejecta components undergoing energy injection in a stratified environment. The model provides multiwavelength light curves and corresponding closure relations for the deep Newtonian regime. We apply this framework to the late-time multiwavelength observations of GRB 171205A. In addition, we constrain the physical properties of quasi-spherical outflows using observations of short GRBs associated with kilonova candidates, together with long-term radio upper limits obtained years after the burst in a broader GRB sample. Our results show that late-time observations can place meaningful constraints on the dynamics, energetics, and energy-injection history of sub-relativistic quasi-spherical outflows from GRB progenitors.

astro-ph.HE↗

arXiv2025

Variation of Microphysical Parameters in Reverse-shock Scenario

Gamma-ray bursts (GRBs), among the most compelling astrophysical phenomena, are potential candidates for exploring the evolution of energy distribution among magnetic fields and particles through multiwavelength observations. The fraction of energy transferred between particles and the magnetic field is governed by microphysical parameters, typically assumed to be constant during relativistic shocks but may in fact vary with time. In this work, we derive the light curves and closure relations (CRs) of the synchrotron-self Compton (SSC) process from the external reverse shock (RS) with variations of microphysical parameters in a homogeneous and stellar-wind medium. We consider the evolution of the RS in the thick- and thin-shell regimes. We demonstrate that, depending on the microphysical parameters, this process can mimic plateau phases and produce temporal decay indices steeper than those predicted by high-latitude emission alone. The current model is employed to examine the evolution of the spectral and temporal indices of GRBs reported in the Second Fermi-LAT Gamma-ray Burst Catalog (2FLGC) and bursts detected at very high energies, using Markov Chain Monte Carlo (MCMC) simulations.

astro-ph.HE↗

arXiv2025

Late-afterglow Emission from a Quasi-spherical Outflow in a stratified environment

Gamma-ray bursts (GRBs) are cosmic events occurring at large distances beyond our galaxy. They provide a unique opportunity to study electromagnetic patterns not seen elsewhere. When the collimated GRB outflow interacts with the outer layers of a star or the wind generated by a binary neutron star merger, it releases energy, forming a quasi-spherical outflow around it. This broad outflow begins to radiate once it has transferred enough energy to the surrounding medium. We have developed a new analytical model that describes the synchrotron afterglow scenario of the quasi-spherical outflow, including factors such as stratified density, self-absorption regime, and the fraction of electrons accelerated by the shock front. We also successfully describe the multiwavelength observations of a sample of llGRB afterglows (GRB 980425, 031203, 060218, 100316D, 130603B, 150101B and 171205A) that exhibited a late component, analyzed in both stellar wind and constant-density environments. Our analysis shows that a constant-density environment is favored. Additionally, we consider the multiwavelength upper limits of the short bursts reported in the Swift-BAT database.

astro-ph.HE↗

arXiv2025

Magnetic Burial in Millisecond Magnetars and Late GRB Afterglow Signatures

Millisecond magnetars, one of the potential candidates for the central engine of Gamma-ray bursts (GRBs), can experience significant magnetic field enhancement shortly after their formation. In some cases, this evolution is further influenced by the accretion of stellar debris, which modifies the dipole magnetic field strength. During a hypercritical accretion phase that lasts seconds or longer after the progenitor explosion, a thin crust may form, submerging the magnetic field (the so-called magnetic burial scenario). Once hypercritical accretion ceases, the buried field can diffuse back through the crust, delaying the external dipole's reactivation. On the other hand, observations have shown that relativistic outflows ejected by these objects and decelerated by the circumburst environment cause a late and temporary emission known as afterglow. This work investigates how the submergence and subsequent reemergence of the magnetar magnetic field, on a few years timescales, affect the GRB afterglow dynamics. Specifically, we apply this phenomenological scenario to the late-time X-ray excess observed approximately three years post-burst in GW170817/GRB 170817A, exploring how the evolving magnetic field strength may contribute to this emission. Our modelling of GRB 170817A indicates that $\gtrsim90$ percent of the external dipole flux was initially buried, re-emerging on a timescale $τ_{B}=3-40$ yr and restoring a surface field $B\simeq(2-5)\times10^{15}\,$G; the late-time X-ray brightening is far better reproduced by this scenario than by models without burial.

astro-ph.HE↗