arXiv subjects

Rin Oikawa

Publications and source records attributed to Rin Oikawa.

3 recordsLinked to original sources

arXiv2026

Launching Jets in Tidal Disruption Events: Magnetic Flux Advection and Plasma Loading

A tidal disruption event (TDE) occurs when a star approaches a black hole (BH) and is disrupted by its tidal forces. Although several hundred TDEs have been identified to date, only a small fraction are accompanied by relativistic jets. These jets are thought to be Poynting-flux-dominated outflows powered by the Blandford--Znajek (BZ) mechanism. However, the origin of the magnetic flux and plasma needed to power BZ jets remain unclear. In this Letter, we propose a scenario in which magnetic flux is initially stored in a pre-existing low-Eddington accretion disk around BH, and is subsequently advected toward the BH by the super-Eddington accretion flow formed after the stellar disruption. We show that stars with low densities, such as red giants, can supply sufficient magnetic flux to power a BZ jet. Once sufficient magnetic flux accumulates near the BH, an equatorial current sheet forms where magnetic reconnection produces high-energy gamma rays. We find that photon--photon pair production by these gamma rays supplies the BH magnetosphere with sufficient plasma to launch and sustain a BZ jet. We further show that this mechanism simultaneously provides enough radiating particles to account for the observed prompt emission.

astro-ph.HE↗

arXiv2026

Non-uniform particle injection into black hole jets by radiative magnetic reconnection

Active galactic nuclei often exhibit highly collimated relativistic plasma outflows launched from the vicinity of their central black holes. One of the key theoretical challenges in understanding black hole jet formation is the origin of the plasma that feeds the jet, which remains poorly understood, particularly in explaining the observed jet emission. In this study, we focus on electron positron pair production generated by high energy photons from non axisymmetric magnetic reconnection near the black hole, as suggested by recent three dimensional general relativistic magnetohydrodynamics simulations. By employing general relativistic ray tracing, we calculate the spatial distribution of the pair production rate in the jet, taking into account photon propagation and collision angles in curved spacetime. We find that our scenario can naturally supply a sufficient amount of plasma to explain the observed radio emission from the M87 jet, even when photon anisotropy is considered. Furthermore, we show that a spinning black hole plays a crucial role in shaping the spartial dsitribution of the pairs, which in turn affects jet acceleration and very high energy emission from the jet base.

astro-ph.HE↗

arXiv2026

Successive Partial Disruptions with Orbital Precession in a White Dwarf-Black Hole System for Repeating GRB 250702B

The peculiar gamma-ray burst GRB 250702B is the longest event ever observed, lasting about one day and exhibiting four prompt-emission flares of $\sim100$ s with irregular recurrence intervals of at least one hour. To explain this hierarchy of timescales, we consider a scenario in which a stellar object undergoes repeated partial tidal disruptions by a black hole (BH). We find that if a white dwarf (WD) is on a highly eccentric orbit ($e\approx0.97$) around an intermediate-mass black hole (BH) with $M_{\rm BH}\lesssim10^{6}\,M_\odot$ and $a = 50\,R_\odot\left(M_{\rm BH}/10^{6}\,M_\odot\right)^{1/3}$, the observed properties of GRB 250702B can be naturally reproduced. In this framework, the duration of each flare is determined by the viscous accretion timescale of material stripped near pericenter, with a typical mass $\Delta M \approx 2\times10^{-2}\,M_\odot$. The minimum recurrence time corresponds to the orbital period, while the total activity period is set by the secular orbital evolution timescale leading to the complete disruption of the WD. Furthermore, if $M_{\rm BH}\gtrsim10^{5}\,M_\odot$ and the orbit has a minimum polar angle relative to the BH equatorial plane of $\theta_{\rm min}\gtrsim0.12 {\rm rad}$, relativistic frame dragging induces $\gtrsim0.1$ rad precession of the orbital angular momentum between successive pericenter passages, comparable to a typical GRB jet half-opening angle, resulting in intermittent alignment with the observer and irregular flare spacing. The WD experiences $\approx40$ jet-launch episodes before complete disruption, but only four are expected to be observed on-axis. The remaining off-axis jets become visible at late times, enhancing the radio afterglow by about an order of magnitude, providing a testable prediction of this scenario.

astro-ph.HE↗