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Abstract In this letter, we investigate Bondi-like accretion flows with zero or low specific angular momentum by performing 3D general relativistic magnetohydrodynamic simulations. In order to check if relativistic jets can be launched magnetically from such flows, we insert a large-scale poloidal magnetic field into the accretion flow and consider a rapidly spinning black hole. We demonstrate that under such conditions the accretion flow needs to initially have specific angular momentum above a certain threshold to eventually reach and robustly sustain the magnetically arrested disk state. If the flow can reach such a state, it can launch very powerful jets at ≳100% energy efficiency. Interestingly, we also find that even when the accretion flow has initial specific angular momentum below the threshold, it can still launch episodic jets with an average energy efficiency of ∼10%. However, the accretion flow has nontypical behaviors such as having different rotation directions at different inclinations and exhibiting persistent outflows along the midplane even in the inner disk region. Our results give plausible explanations as to why jets can be produced from various astrophysical systems that likely lack large gas specific angular momenta, such as Sgr A*, wind-fed X-ray binaries, tidal disruption events, and long-duration gamma-ray bursts. 

Abstract We present the tidal disruption event (TDE) AT2022lri, hosted in a nearby (≈144 Mpc) quiescent galaxy with a low-mass massive black hole (10⁴M_⊙<M_BH< 10⁶M_⊙). AT2022lri belongs to the TDE-H+He subtype. More than 1 Ms of X-ray data were collected with NICER, Swift, and XMM-Newton from 187 to 672 days after peak. The X-ray luminosity gradually declined from 1.5 × 10⁴⁴erg s⁻¹to 1.5 × 10⁴³erg s⁻¹and remains much above the UV and optical luminosity, consistent with a super-Eddington accretion flow viewed face-on. Sporadic strong X-ray dips atop a long-term decline are observed, with a variability timescale of ≈0.5 hr–1 days and amplitude of ≈2–8. When fitted with simple continuum models, the X-ray spectrum is dominated by a thermal disk component with inner temperature going from ∼146 to ∼86 eV. However, there are residual features that peak around 1 keV, which, in some cases, cannot be reproduced by a single broad emission line. We analyzed a subset of time-resolved spectra with two physically motivated models describing a scenario either where ionized absorbers contribute extra absorption and emission lines or where disk reflection plays an important role. Both models provide good and statistically comparable fits, show that the X-ray dips are correlated with drops in the inner disk temperature, and require the existence of subrelativistic (0.1–0.3c) ionized outflows. We propose that the disk temperature fluctuation stems from episodic drops of the mass accretion rate triggered by magnetic instabilities or/and wobbling of the inner accretion disk along the black hole’s spin axis. 

Abstract The ∼100 tidal disruption events (TDEs) observed so far exhibit a wide range of emission properties both at peak and over their lifetimes. Some TDEs radiate predominantly at X-ray energies, while others radiate chiefly at UV and optical wavelengths. While the peak luminosities across TDEs show distinct properties, the evolutionary behavior can also vary between TDEs with similar peak emission properties. In particular, for optical TDEs, while their UV and optical emissions decline somewhat following the fallback pattern, some events can greatly rebrighten in X-rays at late time. In this Letter, we conduct three-dimensional general relativistic radiation magnetohydrodynamics simulations of TDE accretion disks at varying accretion rates in the regime of super-Eddington accretion. We make use of Monte Carlo radiative transfer simulations to calculate the reprocessed spectra at various inclinations and at different evolutionary stages. We confirm the unified model proposed by Dai et al., which predicts that the observed emission largely depends on the viewing angle of the observer with respect to the disk orientation. Furthermore, we find that disks with higher accretion rates have elevated wind and disk densities, which increases the reprocessing of the high-energy radiation and thus generally augments the optical-to-X-ray flux ratio along a particular viewing angle. This implies that at later times, as the accretion level declines, we expect that more X-rays will leak out along intermediate viewing angles. Such dynamical model for TDEs can provide a natural explanation for the diversity in the emission properties observed in TDEs at peak and along their temporal evolution.