Possible periodic features in fast radio bursts (FRBs) may provide insights into their astrophysical origins. Using extensive observations from the five-hundred-meter aperture spherical radio telescope (FAST), we conduct a multi-timescale periodicity search for the exceptionally active repeater FRB 20240114A. Our analysis is based on different datasets for different timescales: for short-timescale periodicity in time of arrivals (TOAs), we use 57 observations from January to August 2024; for long-timescale periodicity, we employ an extended TOA dataset comprising 111 observations spanning from January 2024 to October 2025; and for burst time series analysis, we utilize individual burst data from the 57 FAST observations. We identify three candidate short-timescale periodic signals (0.673, 0.635, and 0.536 s) with significances of 3.2σ-6σ, each detected in two independent observations. On longer timescales, we detect a significant (143.40 ± 7.19)-d periodicity with 5.2σ significance, establishing FRB 20240114A as a periodic repeater. In burst time series, we find quasi-periodic oscillations in the few hundred Hz range (3.4σ and 3.7σ) and periodic burst trains with periods of several to tens of milliseconds (3σ-3.9σ), though these periodic features appear transient and short-lived. The detection of periodic signals at these different timescales indicates that FRB 20240114A exhibits intriguing periodic self-similar characteristics. Despite the comprehensive dataset, no definitive periodicity linked to the source’s rotation is confirmed, placing stringent constraints on the intrinsic source properties and the modulation mechanisms. All data are available via the Science Data Bank.

Recent gravitational-wave (GW) observations have revealed binary black hole (BBH) mergers with both extreme mass ratios and large effective spin parameters (χ_eff). GW241011 is a notable example that shows these properties. Although hierarchical mergers (second-generation + first-generation BHs) can naturally produce high spins, they rarely produce such an extreme mass ratio (∼ 0.3), and are further limited by gravitational recoil kicks that can eject the second-generation BH from the host environment. Moreover, recent studies have argued against a dynamical origin for GW241011. Here, we investigate the formation of GW241011-like systems through the mass-ratio reversal (MRR) channel in isolated binary evolution. By quantifying the probability of producing such systems across a range of binary-evolution models, we identify the key dependencies on stellar-evolution and binary-interaction physics. Our results demonstrate the conditions under which the MRR channel can provide a viable alternative to hierarchical mergers and place constraints on the physical processes governing binary evolution.

The AT2017gfo kilonova transient remains a unique multi-messenger event thanks to its proximity (z = 0.00987) and the possibility to investigate time-resolved spectra, thus providing evidence of r-process nucleosynthesis. The kilonova signal was extensively studied in the spectral and time domains, providing key insights into the chemical composition and physical properties of the ejecta. Here, we report the discovery of a novel correlation between two fundamental observables: the peak energy of the E FE spectrum, Ep, and the isotropic-equivalent luminosity, Liso. In particular, we show that up to about 2.5 days after the merger, the AT2017gfo spectrum evolves according to: log10[Ep/eV] =-0.13+0.02-0.02 + 0.62+0.02-0.02 log10[Liso/(1041 erg s-1)] (68 % C.L.) while in the subsequent epochs, Ep remains almost constant with Liso, flattening around 1 eV. Exploiting simulations from a state-of-the-art radiative transfer code, we demonstrate that our kilonova model inherently predicts this peculiar correlation, hence suggesting a new diagnostic tool for comparing observables against simulations. Future kilonova observations will provide additional insight into the physics behind the Ep-Liso correlation.

Blazars and gamma-ray bursts (GRBs) are both cosmic beacons of extreme energy release powered by relativistic jets. However, they originate from tremendously different environments. Blazars are the sustained powerhouses driven by supermassive black holes at galactic centers, whereas GRBs are the transient death signals of massive stars or merging compact objects. Here we show that, despite the enormous differences, a universal physics defines the radiation spectra of blazars and GRBs. The blazar spectrum is well described by a “log-parabola” function. Employing a simple toy model with a single optically thin region of a decreasing magnetic field, we produce the log-parabola spectrum very naturally for blazars. We find that the blazar spectrum is shaped by the “cooling physics” of relativistic electrons in the fast-cooling regime, which we identify as the universal physics since we previously showed that the fast-cooling physics of electrons with a decreasing magnetic field also explains the mysterious low-energy spectral index of the gamma-ray spectrum for a majority of GRBs. This fast-cooling physics of electrons likely nails down the physical origin underlying the universal scaling of the jet energetics between blazars and GRBs, which was observationally suggested more than a decade ago. We highlight that the spectrum shaper in both blazars and GRBs is the cooling physics, not the acceleration mechanism. This finding is conventional-belief-defying and may open up new avenues in a wide range of astrophysics.

White dwarf (WD) tidal disruption events (TDEs) provide a unique window onto intermediate-mass black holes (IMBHs). We present a multi-messenger view of these systems in two papers. In this paper, we develop an accretion-disk model for WD–TDEs in which the bound debris accretes at extremely super-Eddington rates, ∼ 10^5–10^9 times higher than in typical (main-sequence) TDEs. The model includes magnetic pressure, nuclear-burning heating, wind mass loss, and neutrino production via e^± pair annihilation. At such high accretion rates, the gas and radiation temperatures of the inner flow can reach T≳ 10^9 K, enabling prolific pair production and MeV neutrino emission. We find that the disk is predominantly advection dominated over a broad range of accretion rates, while disk winds can partially cool the flow and reduce the inner temperature. The predicted thermal EM emission is nearly insensitive to the fallback rate in the super-Eddington regime: the luminosity only mildly exceeds the IMBH Eddington luminosity and the spectrum peaks at ∼ 0.1–1 keV, implying detectability with current X-ray facilities such as Einstein Probe. For low-mass IMBHs (∼ 10^3 M_⊙), the disk can also produce a burst of MeV neutrinos with luminosities up to ∼ 10^47 erg s^-1 for ONeMg WD–TDEs, although detectability with current neutrino detectors (e.g., Super-Kamiokande and JUNO) is limited to Galactic distances. Finally, we estimate the GW burst produced during the final passage prior to disruption, which peaks at ∼ 0.1–1 Hz, placing WD–TDEs in the target band of proposed decihertz detectors and motivating coordinated GW+EM+neutrino searches. We also present a first exploration of GWs from a precessing WD–TDE disk; this signal is much weaker, with a detection horizon ≲ 1 Mpc for these missions.

FRB 20240114A is an extremely active repeating fast radio burst for which plasma lensing has been proposed to explain its burst-rate variations, spectral evolution, and apparently “carbon-copy” burst pairs. Using FAST data and publicly available Parkes observations, we test this interpretation with a one-dimensional Gaussian plasma-lens model. Although the burst-rate enhancements can be fitted separately, the corresponding magnification peaks and demagnification troughs are offset by far more than predicted and show no consistent periodicity. Moreover, with more than 10,000 bursts detected, a few apparently “carbon-copy” pairs can readily occur by chance. The burst bandwidth is not systematically narrower during the proposed lensing interval, nor are the burst energies significantly enhanced during the predicted magnification interval. These results provide no compelling evidence that a single Gaussian plasma lens explains the observed variability, which is more likely dominated by intrinsic source activity.

This study investigates the morphological classification and drifting rate measurement of the repeating fast radio burst (FRB) source FRB 20240114A using the Five-hundred-meter Aperture Spherical Telescope. Detected on 2024 January 14, FRB 20240114A exhibited an exceptionally high burst rate, revealing unique properties. Through observational campaigns over several months, we selected a data set comprising 3203 bursts (2109 burst clusters) during a continuous monitoring session (15,780 s) on 2024 March 12. Improving upon previous work, we clarify the definitions of sub-bursts, bursts, and burst clusters. Using an average dispersion measures of 529.2 pc cm ^−3 , we classified the burst clusters into Downward Drifting, Upward Drifting, No Drifting, No Evidence for Drifting, Not-Clear, and Complex burst clusters. Among the 978 burst clusters that exhibit drifting behavior, 233 (23.82%) show upward drifting. Additionally, if 142 upward-drifting single-component burst clusters are excluded, upward-drifting double- and multicomponent burst clusters still account for 10.89% of the 836 burst clusters exhibiting drifting behavior, equating to 91 burst clusters. Furthermore, if only upward-drifting burst clusters with consecutive time intervals (or upward-drifting bursts) are considered, only nine bursts remain. Drifting rate comparisons with other physical quantities reveal that the drifting rate increases with peak frequency for single-component burst clusters with drifting behavior. Moreover, in single-component burst clusters, those with upward drifting exhibit smaller effective widths, bandwidths, and fluxes than their downward-drifting counterparts. A Kolmogorov–Smirnov test further indicates that upward-drifting burst clusters possess longer consecutive time intervals than downward-drifting ones, suggesting distinct underlying physical mechanisms.

Fast radio bursts (FRBs), highly polarized, mostly have a nearly constant polarization position angle (PA) during each burst. Their PAs are observed to vary from burst to burst, with the statistical properties remaining stable across different observation sessions. We found that the intrinsic PAs of repeating FRBs are approximately Gaussian distributed, suggesting that the emission likely originates from a localized region within the neutron star's magnetosphere. A periodicity search of the PA time series using the Lomb-Scargle periodogram reveals no credible periodic signal in the period range from 10 ms to 10^7 ms, and similar analyses of several active observations also yield null detections. We interpret these properties by extending the rotating vector model to include a dynamically evolving magnetosphere, in which the effective magnetic axis varies from burst to burst due to stochastic perturbations. In this framework, the observed PA distributions can naturally arise from geometric projection effects, and the absence of periodicity reflects the random wandering of the magnetic axis within a confined region. This scenario provides a natural explanation for both repeating and apparently non-repeating FRBs.

Massive stars die as core-collapse supernovae, whose optical light emerges days after the implosion. Theory predicts that the initial collapse-driven shock, upon breaking through the star and dense circumstellar medium, emits a brief thermal flash of soft X-rays and ultraviolet. Yet these elusive first signals have remained largely undetected, owing to limited wide-field soft X-ray monitoring. Here we report the discovery of a soft X-ray flash, EP260321a, followed days later by a broad-lined supernova from an envelope-stripped progenitor. Its X-ray spectrum, best modeled with blackbody, establishes it as the long-sought archetypal shock breakout. The burst's duration and energetics place the breakout at a radius of 300 solar radii, tracing a dense surrounding shell and revealing abrupt mass ejection within the final month before collapse.

The formation channels of magnetars remain an open question. Although core-collapse supernovae of isolated massive stars are important, binary interactions—such as tidal interaction, common envelope evolution, and stellar mergers—may also play a significant role in making magnetars. Understanding the relative contributions of these channels is crucial for linking magnetars to their observed properties and host environments. In this paper, we investigate potential magnetar formation channels using population synthesis simulations, considering both single-star and isolated binary system evolution. By conducting simulations with different parameters, we compare the effects of various evolution processes on magnetar formation. Additionally, we study the delay times and kick velocities across all formation channels, and analyze the orbital properties and companion types of surviving magnetar binaries. We find that the majority of magnetars are observed as single objects (≥90%), although a large fraction of them were originally in binary systems and experienced either a kick disruption or merger. Surviving binaries are most likely to host main-sequence companions and exhibit different distributions of eccentricities due to different supernova mechanisms. These findings show the critical role of binary evolution in magnetar formation and provide predictions for the properties of magnetar populations that can be tested with future observations.

Recently, polarization angle (PA) orthogonal jumps over millisecond timescales were discovered from three bursts of the repeating fast radio burst source FRB 20201124A by the FAST telescope. In general, PA jumps can arise from the coherent or incoherent superposition of two electromagnetic waves, with the total polarization fraction remaining constant in the former and not in the latter. The observations seem to be more consistent with incoherent superposition. The amplitudes of the two orthogonal modes are required to be comparable when jumps occur. We provide general constraints on FRB emission and propagation mechanisms based on the data. Physically, it is difficult to produce PA jumps through switching the dominance of the two orthogonal modes within millisecond timescales, and a geometric effect due to rotation of the source is more plausible. This requires that the emission region be within the magnetosphere of a spinning central engine, likely a magnetar. The two orthogonal modes in different directions can arise when the rotation of the source brings two independent emission regions with different dominant modes successively into the line of sight, due to either intrinsic radiation mechanisms or the O-mode undergoing a delayed transparency because of the Alfvén–O-mode conversion. Splitting of emission directions for the two modes due to plasma birefringence is not easy to achieve when the plasma is moving relativistically. For intrinsic radiation mechanisms, curvature radiation always predicts ∣ E _X / E _O ∣ ≳ 1, and it is difficult to produce jumps; whereas inverse Compton scattering can achieve the conversion amplitude ratio ∣ E _X / E _O ∣ = 1 to allow jumps to occur under special geometric configurations.

Polarization measurements of fast radio bursts (FRBs) probe the magnetized plasma surrounding their central engines. FRB 20240114A is an exceptionally active repeating source, with 17,356 bursts detected between 2024 January 28 and 2025 May 30 by FAST, enabling studies of the temporal evolution of its polarization properties. In this work, we present a polarimetric catalog of 6131 bright bursts (with a signal-to-noise ratio (S/N) >= 20, 35.3% of the total sample), including arrival time (MJDtopo), dispersion measure (DM), burst width (Weff), bandwidth, Faraday rotation measure (RM), linear and circular polarization degrees (L/I, V/I), and intrinsic polarization angle (PA0). We confirm a clear temporal evolution of RM: after an initial stable phase, it decreases linearly by similar to 200 rad m-2 over 200 days, forming a bimodal distribution, whereas DM remains stable at 529.3 +/- 1.2 pc cm-3. The linear polarization fraction is generally high, with the 3 sigma lower bound around 76%, while circular polarization is low, with 1157 of 17,356 bursts (6.67%) having divided by V divided by/I >= 10%. We perform a power-law fit between divided by V divided by/I and divided by RM divided by, which yields an index of -2.98 +/- 0.80. It is found that the combined 2D distribution of L/I versus V/I remains stable, implying that the emission mechanism is largely invariant. Our PA0 measurements show a broad, nonuniform distribution, implying a complex emission geometry. These results suggest that FRB 20240114A resides in a dynamically evolving magneto-ionic environment. This catalog provides a foundation for studies of repeating FRB progenitors and their environments.

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients, some of which are associated with compact persistent radio sources (PRSs), hinting at a physical connection. While several models have been proposed to explain PRSs and their connection to FRBs, direct observational tests remain limited. Here, we report for the first time a correlated trend between the long-term variation of the PRS flux density and the burst energetics of FRB 20190520B and FRB 20240114A, suggesting a physical coupling between the PRS and FRB activity. We further examine additional repeaters with compact PRSs and find no clear correlation between PRS luminosity and burst activity, likely due to the limited observations. These results are consistent with scenarios in which both the PRS and FRB activity may be powered by a common energy reservoir, such as the magnetic or rotational energy of a magnetar.

The magnetar 1E 1841-045 exhibited a new active episode starting on 2024 August 20, marked by X-ray bursts and enhanced persistent emission. Using data from the Einstein Probe (EP), we report on the timing and spectral results following the onset of this outburst. The pulse profile displays a multipeaked structure, with notable phase shifts in the secondary peak. Energy-resolved pulse profile analysis indicates a transition in the dominant peak of the pulse profile above 5.8 keV. The 0.5-10 keV X-ray spectrum is well modeled by a combined blackbody and power-law (BB+PL) model, showing a similar to 20% flux increase following the outburst. Phase-resolved spectroscopy indicates a correlation between BB temperature and pulse profile intensity, along with spectral hardening at a specific pulse phase. The high spatial resolution of EP enables effective separation of the supernova remnant emission, which is crucial for measuring the intrinsic pulse emission of the source. These findings underscore the intricate relationship between magnetar outbursts, pulse profile evolution, and spectral characteristics.

Gamma-ray bursts (GRBs) are generally classified as Type I GRBs, which originate from compact binary mergers, and Type II GRBs, which originate from massive collapsars. The traditional correspondence between short Type I GRBs and long Type II GRBs, separated by a duration of 2 s, has been challenged by recent observations of long GRBs associated with kilonovae (i.e., Type I-L GRBs) and a short GRB associated with a supernova. In this paper, we focus on GRBs with precursor emission (PE) and compile 366 GRBs detected by Fermi/GBM. Applying the unsupervised machine learning methods t-distributed stochastic neighbor embedding and uniform manifold approximation and projection, we are able to distinguish Type I (including subclass Type I-L) and Type II GRBs for the first time and identify PE as a key feature for distinguishing GRBs of different origins. Inspired by results of machine learning, we propose a diagnostic parameter, the E-p,E-ME-precursor index (EPI), defined as log 10 (E-p,ME(2)/(T-100,T- PE T-100 , QE1 (1/2) T-MV T,T- PE)), where most Type I GRBs have EPI > 6.2 and most Type II GRBs have EPI < 6.2. This parameter can help the community to diagnose the origin of any GRB with PE based solely on its prompt emission and rapidly plan for follow-up observations. The validation using Swift GRBs provides illustrative evidence that our method may also be applicable to GRBs observed by instruments other than Fermi.

GRB 221009A is the brightest gamma-ray burst observed to date. We analyze its precursor and Phase I of the main burst, using Fermi/Gamma-ray Burst Monitor data and aiming to investigate the jet composition during these two phases of the prompt emission. We find that spectral analyses reveal thermal emission in both phases. Within the framework of the hybrid jet model of Gao & Zhang, the dimensionless entropy η and magnetization parameter (1 + σ _0 ) significantly exceed unity, indicating a substantial contribution from the Poynting-flux component in addition to the thermal fireball component in the prompt emission jet. For an engine radius of ∼10 ^7 cm, the time-resolved magnetization parameter $(1+{\sigma }_{{r}_{15}})$ is essentially unity in both phases, suggesting that the nonthermal emission may originate from internal shock (IS). Furthermore, the Lorentz factor Γ _ph and photospheric radius r _ph derived at this engine radius are also consistent with the values and evolutionary behavior expected from the fireball model. In the case r _0 ∼ 10 ^8 cm, the precursor suggests that the nonthermal radiation may still arise from IS, whereas portions of the main burst are likely produced by ICMART events. Nonetheless, independent of whether IS or ICMART dominates, the jet consistently carries a significant Poynting flux. Additionally, both phases exhibit broadly similar correlations of kT _obs and E _p with F _obs , as well as a positive Γ _ph – L _γ _,iso relation. These results suggest that the precursor and main burst Phase I share common properties and likely originate from the same physical source.

EP241113a, a soft X-ray transient detected by the Einstein Probe (EP), has an isotropic-equivalent energy (E_γ,iso∼ 10^51 erg) comparable to classical gamma-ray bursts (GRBs) but an exceptionally low peak energy (E_p≲ 1 keV), placing it off the canonical E_p–E_γ,iso (Amati) relation at >3σ confidence. The afterglow of EP241113a is also unusual, with an extremely low plateau luminosity and no jet break up to the latest observation. Such properties have been interpreted as arising from an energetic “dirty fireball,” i.e., a relativistic jet with energy comparable to classical GRBs but much higher baryon loading, leading to a bulk Lorentz factor of Γ∼ 20. In this Letter, we propose that low E_p arises from dissipative photospheric emission in such a low-Γ jet. As Γ decreases, the photosphere shifts outward while the internal shock radius moves inward, causing dissipation to occur well below the photosphere and making the prompt emission photosphere-dominated. Meanwhile, the thermalization radius also moves outward, reducing the comoving radiation temperature where the spectral peak is established. Combined with weaker Lorentz boosting, these effects naturally shift the observed E_p into the soft X-ray band. We further suggest that such a low-Γ jet may be powered by neutrino–antineutrino (ν) annihilation in a hyperaccreting disk formed during the core collapse of a massive star. Compared with the Blandford–Znajek process, neutrino annihilation can produce a dirtier jet through baryon entrainment from a neutrino-driven wind. EP241113a-like events therefore offer new insight into the dissipation physics and launching mechanisms of jets from collapsing massive stars.

Context. Unstable mass transfer may occur during white dwarf–neutron star (WD–NS) mergers, in which the WD can be tidally disrupted and form an accretion disk around the NS. Such an accretion disk can produce unbound wind ejecta with synthesized 56Ni mixed in. Numerical simulations reveal that this unbound ejecta should be strongly polar-dominated, which may cause the subsequent radioactive-powered thermal transient to be viewing-angle-dependent–an issue that has so far received limited investigation. Aims. We investigated how the intrinsically nonspherical geometry of WD–NS wind ejecta affects the viewing-angle dependence of the thermal transients. Methods. Using a two-dimensional axisymmetric ejecta configuration and incorporating heating from the radioactive decay of 56Ni, we employed a semi-analytical discretization scheme to simulate the observed viewing-angle-dependent photospheric evolution, as well as the resulting spectra and light curves. Results. The observed photosphere evolves over time and shows a strong dependence on the viewing angle: off-axis observers can see deeper, hotter inner layers of the ejecta and larger projected photospheric areas compared to on-axis observers. For a fiducial WD–NS merger producing 0.3 M⊙ of ejecta and 0.01 M⊙ of synthesized 56Ni, the resulting peak optical absolute magnitudes of the transient span from ≃ − 12 mag along the polar direction to ≃ − 16 mag along the equatorial direction, corresponding to luminosities of ∼1040–1042 erg s−1. The typical peak timescales are expected to be 3–10 d. Conclusions. We present the first exploration of the viewing-angle effect on WD–NS merger transients. Since their ejecta composition and energy sources resemble those of supernovae, yet WD–NS merger transients are dimmer and evolve more rapidly, we propose using “mini-supernovae” to describe the thermal emission following WD–NS mergers. Our study highlights the critical role of geometry in the interpretation of WD–NS mini-supernovae and motivates further exploration of their diversity in observation.

The potential association between gravitational waves (GWs) and fast radio bursts offers a unique multimessenger probe for cosmology. In this paper, we develop a redshift-independent framework to constrain cosmological parameters using the luminosity distance–dispersion measure (DM) relation, accounting for realistic astrophysical uncertainties. We perform a comprehensive comparative analysis across different GW detector sensitivities and modeling assumptions. Specifically, we investigate the performance of the current LIGO-Virgo (LV) network (at z < 0.2) versus the future Cosmic Explorer (CE). Our study further evaluates the impact of different DM distributions—specifically the corrected Macquart’s probability density function (Zhuge et al. 2026) and the log-normal distribution—and explores the influence of including or excluding host galaxy DM contributions. Using realistic simulated observations, we find that while the current LV network lacks the precision to provide meaningful constraints, CE will enable high-precision cosmology. Even without spectroscopic redshifts, CE observations can effectively break parameter degeneracies and robustly constrain both cosmology and host galaxy parameters. These results highlight the necessity of next-generation detectors.