arXiv subjects

Tao An

Publications and source records attributed to Tao An.

At least 19 recordsLinked to original sources

arXiv2026

EP250302a: violent shell collision in a soft-X-ray-selected GRB-like transient

The Einstein Probe opens a previously unexplored soft X-ray window onto gamma-ray bursts, filling a critical observational gap in the soft X-ray coverage of their prompt emission. In this letter, we present EP250302a, a soft-X-ray-selected, GRB-like transient at $z=1.131$ detected by the Einstein Probe. Follow-up observations from X-ray to radio reveal a narrow X-ray flare at $\sim 1.1$\, ks and subsequent achromatic optical and X-ray rebrightening. These features challenge a standard single-component afterglow model and indicate the need for multiple ejecta components. A violent collision between a late relativistic shell and the decelerated leading blast wave provides a plausible interpretation: the flare arises from internal dissipation of the late ejecta, while the rebrightening is powered by the shocked emission produced in the collision. Quantitative modeling constrains the kinetic energy ratio between the late shell and the initial ejecta to $E_{\rm k,iso,2}/E_{\rm k,iso,1} \sim 5$ (with $E_{\rm k,iso,2} \sim 10^{53}$~erg and $E_{\rm k,iso,1} \sim 2\times10^{52}$~erg), as well as the Lorentz factor contrast to $Γ_{2,0}/Γ_{1,0} \approx 0.98$--$2.27$, required to reproduce the observed flare luminosity and rebrightening amplitude. Such an energetic late shell can be launched in a radiatively inefficient second episode of central-engine activity. Thanks to the well-sampled, early-time multiband coverage facilitated by the EP trigger, EP250302a provides a valuable case to test the physical connection between central-engine activity and shell collisions.

astro-ph.HE↗

arXiv2026

Searching for Black Hole Candidates in Quiescence by Using Multi-band Observations in Globular Cluster M22 (NGC 6656)

We present a multi-wavelength investigation of radio sources in the globular cluster M22 (NGC 6656) using the Karl G. Jansky Very Large Array, Chandra and Hubble Space Telescope. By cross-matching the radio and X-ray source catalogs, we identify eight radio/X-ray counterparts, of which VLA22 is the most promising stellar-mass black hole (BH) candidate. Its radio and X-ray luminosities are consistent with the established $L_{\rm X}-L_{\rm R}$ correlation for BH low-mass X-ray binaries. The observed X-ray variability supports an accreting nature. One possible optical counterpart ($M_{\mathrm{814}} \approx 16.695 \pm 0.011$ mag) is identified. Based on its inferred stellar parameters, the estimated orbital period of $P_{\rm orb} \sim 16 \pm 6~{\rm h}$ places the proposed counterpart predominantly in the BH region rather than in the NS region in the $L_{\rm X}-P_{\rm orb}$ plane. These results demonstrate the effectiveness of joint radio, X-ray, and optical observations in identifying quiescent BH candidates in globular clusters.

astro-ph.HE↗

arXiv2026

SN 2025fhm: A central-engine powered Ic-BL supernova associated with X-ray transient EP250304a

We present X-ray, optical, and radio follow-up observations of EP250304a, an extragalactic fast X-ray transient (EFXT) discovered by the Einstein Probe. Its X-ray light curve exhibits two broad pulses with comparable peak fluxes within the first $\sim$1~ks, a feature rarely seen among low-luminosity gamma-ray bursts or EFXTs. Optical follow-up observations were carried out using the Korea Microlensing Telescope Network, the Thai Robotic Telescope, the Las Cumbres Observatory 1~m global network, the Gemini Multi-Object Spectrograph on Gemini south telescope, and the Global Supernova Network. The fast-cooling phase (within 3 days) of optical data can be well fitted by a shocked cocoon model. However, during the supernova phase (SN 2025fhm, from 3 to 88 days), the late-time light curve cannot be explained solely by radioactive $^{56}$Ni decay, as demonstrated by a grid of simulations using the one-dimensional Lagrangian radiation hydrodynamics code SNEC, which reveals a significant energy excess at late epochs. To account for this excess, a central engine like a rapidly spinning, highly magnetized neutron star is needed to provide additional energy injection. This model yields a best-fit spin period of $\sim$12.60~ms and magnetic field strength of $\sim 3.52\times10^{15} \rm G$, and it successfully explains both the late-time bolometric light curve and the early X-ray pulse structures. Our results indicate that EP250304a/SN 2025fhm is likely powered by a central magnetar rather than by radioactive decay alone, offering new insights into the energy budget and physical origin of EFXTs and their associated supernovae.

astro-ph.HE↗

arXiv2026

The Intermediate-Mass Black Hole Reverberation Mapping Project: Scientific Overview and Sample Characteristics

Recent discoveries with the James Webb Space Telescope of massive black holes at high redshift have highlighted fundamental questions about black hole seed formation and the coevolution of black holes with their host galaxies. Because the initial seed population cannot yet be observed directly, nearby intermediate-mass black holes provide a complementary fossil record of black hole formation and early growth. Motivated by this opportunity, we present the Intermediate-Mass Black Hole Reverberation Mapping (IMBH-RM) project and construct a homogeneous Sloan Digital Sky Survey sample of active broad-line IMBHs by uniformly reanalyzing literature candidates with consistent spectral decomposition and black hole mass estimation. Our sample contains 192 reliable IMBH candidates at $z\lesssim0.3$ with $\log(M_{\rm BH}/M_\odot)<6$, including four particularly compelling sources with $\log(M_{\rm BH}/M_\odot)<5$. The primary goal of IMBH-RM is to obtain reliable black hole masses from direct measurements and characteristic sizes of the broad-line region and accretion disk for a carefully selected subsample. These measurements will provide robust low-mass anchors for calibrating single-epoch black hole mass estimates and extending black hole--galaxy scaling relations into the IMBH regime. By building a statistically meaningful reverberation-mapped sample spanning $10^4-10^6\,M_\odot$, we aim to constrain the local IMBH mass distribution and place observational constraints on competing black hole seed formation scenarios. The future Multi-Channel Imager aboard the Chinese Space-station Survey Telescope provides a particularly promising platform for achieving these goals.

astro-ph.GA↗

arXiv2026

Ultra-Precise Astrometric Search for Exoplanets with SKA-VLBI

The study of exoplanets is a rapidly developing field, driven by the discoveries of Kepler and TESS, among others. The recent detection of Jovian planetary companions of low-mass stars demonstrates that VLBI observations will be an excellent tool for indirect detection of planetary companions through precise radio astrometry of the host star. The anticipated sensitivity of SKA-VLBI and its capability to form multi-beam Tied Array Beams and MultiView analysis will allow us to achieve an order of magnitude increase in astrometric precision, providing much finer details for a wider range of exoplanets and hosts, which will revolutionize the field of exoplanets. Precise micro-arcsecond astrometric observations are crucial for detecting not only Jupiter-like planets, but also lower-mass planets. SKA-VLBI astrometric observations in L and C bands will open the possibility of indirect detection of thousands of planetary companions to radio-bright ultra cool dwarfs, M dwarfs and young stars. When a companion is also detected, the astrometric fit of the data will provide the dynamical masses of the components. In the case of binary systems with planets, fitting the astrometric data will provide the individual masses of stars and planets, as well as the mutual inclination angle of the system, which will show whether the planet is moving in prograde or retrograde orbit around its host star. The search for exoplanets at radio wavelengths will be complementary to other techniques and will allow for the detection of a population of exoplanets that is difficult to reach using other techniques.

astro-ph.EP↗

arXiv2026

The Total and Polarized Radio Emission from the Innermost Jets of a High-Redshift Quasar and a Candidate at Parsec-Scale Resolution

High-frequency very long baseline interferometry (VLBI) polarimetry probes synchrotron-emitting plasma closer to the central engines of radio-loud active galactic nuclei (AGNs), but observations above 43 GHz are technically demanding. We present 22-GHz European VLBI Network observations of the $z=4.31$ quasar J1510+5702 and J1606+3124, whose published spectroscopic redshift, $z=4.56$, is uncertain; a photometric estimate gives $z_{\rm phot}=0.9\pm0.1$. For the published $z>4$ redshifts, 22 GHz corresponds to rest-frame frequencies above 118 GHz. Polarized emission is detected in J1510+5702, and a low-level polarized signal is recovered from the brightest feature of J1606+3124. Adopting $z=4.56$, that feature has a brightness temperature of $T_{\mathrm{b,VLBI}}=(7.4\pm0.8)\cdot10^{10}$ K, allowing a mildly Doppler-boosted interpretation, while the young compact-source scenario also remains viable. The core of J1510+5702 has $T_{\mathrm{b,VLBI}}=(1.08\pm0.15) \cdot10^{12}$ K, implying a Doppler factor of ${\sim}22$ under the equipartition assumption. This component has a ${\sim}3.5$ % fractional polarization. These observations show that cm-wavelength VLBI can access rest-frame millimeter-band polarization in bright $z>4$ jets.

astro-ph.GA↗

arXiv2026

Fidelity Before Structure: Verbatim Chunks Beat Lossy Artifact Extraction in Long-Conversation LLM Memory

A growing class of conversational-memory systems compresses dialogue history into structured artifacts (extracted facts, decisions, or events) on the premise that distilled structure retrieves better than raw text. We test this premise with a controlled ablation: within one fixed retrieval--rerank--reasoning pipeline, we swap only the stored representation (LLM-extracted typed artifacts versus verbatim conversation chunks), holding the model, retriever, reranker, and judge constant. Verbatim chunks win by 15.9 points on LoCoMo (43.9% vs. 28.0%) and 22.0 points on LongMemEval-S (67.4% vs. 45.4%); a 1-hop semantic graph does not recover the gap, and six confound controls reproduce the effect. The mechanism is lossy distillation, not structure per se: accuracy tracks how much source text survives in the store, and the extracted-artifact pipeline does not beat naive RAG in overall accuracy (though chunks abstain worse; see Limitations). For the extraction designs we test, structured memory should augment verbatim text rather than replace it: adding artifacts alongside chunks preserves accuracy; substituting them forfeits the gap. Code and data: https://github.com/tao-hpu/cog-canvas

cs.AI↗

arXiv2026

X-rays breaking out of pre-explosion ejecta mark a supernova's first light

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.

astro-ph.HE↗

arXiv2026

Advancing Astrophysics with the SKA II

Advancing Astrophysics with the SKA II (AASKAII), written by our science community, outlines the transformative scientific advances that will be enabled by the SKA telescopes. In the decade since the publication of the previous edition, telescope designs have matured, construction has commenced, and the SKA Organisation has evolved into the SKA Observatory (SKAO). At the same time, observations from SKA precursor and pathfinder telescopes have provided new insights into longstanding scientific challenges while revealing entirely new phenomena. Published in advance of the first science verification campaign for the SKA Observatory, this volume looks ahead to the coming decades of discovery and innovation in radio astronomy. AASKAII spans the broad range of scientific research enabled by the SKA telescopes, SKA-Mid and SKA-Low. The contributions are organised into six thematic categories according to their scientific focus. The opening section presents overview chapters from the SKA Science Working Groups, around which our community is organised. Each overview provides the broader context that connects the contributions in this volume to the key scientific questions being pursued by their respective communities.

astro-ph.IM↗

arXiv2026

The SKA-VLBI Perspective on Radio-Quiet AGN

The accretion-ejection mechanism in Active Galactic Nuclei (AGN) remains a central open problem in astrophysics, tied to the role of AGN feedback in galaxy formation and evolution. Radio-quiet AGN dominate the observed AGN population. Lacking luminous jets, their radio emission traces a rich set of processes spanning the host galaxy kpc scales down to the vicinity of the supermassive black hole: star formation, AGN-driven winds and shocks, free-free emission from photo-ionized gas, low-power jets, and coronal activity close to the inner accretion disk. The Square Kilometre Array (SKA) will probe these processes across a wide frequency range with unprecedented sensitivity, wide-field survey capability, and, critically, high-resolution VLBI imaging. Flux, spectral, and polarization monitoring will constrain dynamics and environmental coupling, while mapping nuclear regions on sub-pc to kpc scales will disentangle compact cores from host emission, resolving the diversity of radio activity across accretion regimes and jet powers from the local Universe to the cosmic dawn. At the full AA4 deployment, the SKA-MID phased into global VLBI arrays will deliver sub-milliarcsecond imaging and $μ$Jy sensitivity over 0.35--15\,GHz, enabling the first population-level census of radio-quiet AGN nuclei. Earlier AA$\ast$ operations will support pilot studies of the brightest nearby systems.

astro-ph.GA↗

arXiv2026

Transforming X-ray Binary Astrophysics with SKA+VLBI

X-ray binaries (XRBs) are unique laboratories where accretion, jets, strong gravity and magnetic fields can be probed on humanly tractable timescales. The phased SKA-Mid operating as a single, ultra-sensitive Very Long Baseline Interferometry (VLBI) element will transform radio studies of XRBs primarily through its time-domain capabilities: substantially improved sensitivity on VLBI baselines that include SKA-Mid in Bands 2 and 5, together with connected-element SKA-Mid imaging extending down to 0.35--1 GHz (Band 1), microarcsecond-precision astrometry for bright systems, high-fidelity polarimetry for the most strongly polarized sources, and rapid target-of-opportunity response. In synergy with global VLBI networks, SKA+VLBI will track the evolution of compact ejecta and compact jets on astronomical unit (AU) scales, measure frequency-dependent core shifts to infer magnetic field strengths and gradients, resolve disk--jet coupling during state transitions in real time, and determine precise distances and natal kicks via parallaxes and proper motions. Joint campaigns with future X-ray and optical telescopes will enable strictly simultaneous, multi-band constraints on accretion--ejection physics and on jet composition. We outline a quantitative program for \aastar\ and AA4, including cadenced, multi-frequency VLBI ``movies'' of jets over the first days of outbursts, an XRB astrometric census, and a core-shift survey, and we provide representative detection rates, magnetic field measurements and distance accuracies. These outcomes will set the microphysical foundation for jet physics across the mass scale from stellar-mass black holes and neutron stars to active galactic nuclei, and will establish SKA+VLBI as the definitive facility for time-domain, high-resolution XRB astrophysics.

astro-ph.HE↗

arXiv2026

Unraveling the mysteries of supernovae with SKA+VLBI

Supernovae (SNe) drive cosmic chemical enrichment and shape galactic feedback, yet the link between progenitors and explosion outcomes remains poorly constrained because the earliest phases are rarely resolved. Radio emission traces synchrotron radiation where the fastest ejecta interact with the circumstellar medium (CSM), providing a uniquely penetrating probe of these phases. SKA-Mid phased into global VLBI will move from simple detections to routine interferometric imaging of nearby extragalactic SNe. Sub-$μ$Jy sensitivity and mas-scale SKA+VLBI imaging, complemented by visibility-domain model fitting for sub-beam radius measurements at 5-15 GHz will allow us to follow the expanding shocks of stripped-envelope SNe out to $\sim$25 Mpc, measure deceleration indices ($m$) and axial ratios to $\approx 5-10\%$, and directly test jet-assisted versus neutrino-driven explosion mechanisms. For interacting SNe (Type IIn/Ibn), SKA+VLBI will resolve clumpy and toroidal CSM on progenitor scales, constraining the timing and geometry of eruptive pre-explosion mass loss. Deep limits on Type Ia SNe will tightly restrict the allowed single-degenerate parameter space, while late-time imaging will search for nascent compact remnants and pulsar wind nebulae. In synergy with optical, X-ray and gravitational wave facilities, SKA+VLBI will turn nearby SNe into laboratories for time-resolved shock physics and progenitor mapping.

astro-ph.HE↗

arXiv2026

Exploring Tidal Disruption Events with SKA and VLBI: Unveiling the Mystery of Black Hole Feeding and Outflows

Tidal disruption events (TDEs) probe the birth and evolution of black hole accretion flows and jets on human timescales. Radio emission traces shocks and outflows from thermal TDEs and powerful relativistic jets in the rare jetted class. SKA Mid, phased for VLBI and used together with global networks, will deliver milliarcsecond imaging, tens of microarcsecond astrometry, and microJy sensitivity, enabling: (i) proper motion measurements that discriminate off axis relativistic jets from subrelativistic winds; (ii) resolved morphologies and magnetic field diagnostics via polarimetry; and (iii) precise nuclear localization to distinguish SMBH vs. IMBH and to reveal recoiling or binary systems. SKA's wide frequency coverage (0.35 to 15.4 GHz) and 1h continuum sensitivities of 3 to 10 microJy per beam, together with multibeam tiedarray VLBI and a transient buffer for rapid triggers, are transformational. LSST, Einstein Probe, and SVOM will increase TDE alerts to hundreds per year, and late time radio flares appear common, ensuring rich SKA VLBI samples. We provide observing strategies, detection forecasts, and predictions, e.g., about 5 proper motion detections of jetted (or off axis) TDEs per year and routine core shift constraints at the microarcsecond level. This program will establish TDEs as laboratories for exploring jet launching, particle acceleration (including neutrinos), black hole accretion history and demographics, and properties of circumnuclear medium.

astro-ph.HE↗

arXiv2026

Gamma-ray Bursts in the Radio Sky: the Role of the SKA-VLBI

Radio observations of $γ$-ray bursts (GRBs) employing the very long baseline interferometry (VLBI) technique provide us with fundamental information on the dynamics and the geometry of the GRB blast wave. With its high angular resolution ($\sim$milli-arcsecond), VLBI allows us to measure the apparent superluminal expansion, to characterise the structure of the jet and to constrain the viewing angle and jet opening angle. While this information is crucial to understand these transient events, such studies have been possible only for three GRBs to date, owing to both the poor sensitivity of current radio facilities and the paucity of close and bright GRBs. In this chapter, we estimate the impact that the SKA-Mid will have on these studies, when included in a VLBI network. We performed a series of dedicated simulations of VLBI observations of GRBs, considering five VLBI networks and the SKA-Mid, both in its AA* and AA4 configurations. We show that including the SKA-Mid in a global-VLBI experiment will: (i) allow us to measure the size and the expansion of a GRB up to a redshift $z\simeq 0.25$ (at a confidence level of $3σ$); (ii) constrain the size $\gtrsim$2 times better than the current global-VLBI array; (iii) improve the localisation precision in Declination from 4 to 30 times; (iv) detect the apparent proper motion of GRBs seen slightly off-axis with a confidence level 3 times better than current VLBI networks. Ultimately, the SKA-Mid will open a new window on a portion of the GRB population that has been inaccessible so far.

astro-ph.HE↗

arXiv2026

Extending the SKA Across Africa: The Case for a Continental African VLBI Network

The African continent holds the key to unlocking the full potential of global Very Long Baseline Interferometry (VLBI). Strategic placement of radio telescopes across Africa provides the crucial north-south and intermediate baselines that are currently missing from the global VLBI network. This expansion will dramatically enhance imaging fidelity and resolution. In this chapter, we propose a vision for a continental African VLBI Network (AVN) that will operate in close synergy with SKA-Mid, enabling transformational science across all cosmic scales. While only the Hartebeesthoek Radio Astronomy Observatory (HartRAO) in South Africa and the Ghana Radio Astronomy Observatory (GRAO) are currently operational, several partner countries are in the process of refurbishing or converting existing antennas. Here, we advocate for the expansion of this network through the deployment of a limited number of SKA-Mid-type telescopes across the continent, creating an "African arm" of SKA-VLBI. With a maximum baseline of ~ 9000 km (from Rabat, Morocco to Cassis, Mauritius), the proposed continental facility will surpass for example, the resolution that will be achieved by the next generation Very Large Array (ngVLA) by ~ 10 % at similar observing frequencies and significantly enhance global VLBI coverage. Beyond the scientific and technical gains, the AVN represents a unique opportunity for sustainable growth in human capital, education, and innovation across Africa. Developing and operating a continental VLBI array will train the next generation of engineers, data scientists, and astronomers, stimulate local industry, and inspire public engagement in science and technology. We outline the current status, challenges, and potential roadmap towards realizing this vision, and we highlight how a continental African VLBI network will position Africa at the forefront of global radio astronomy.

astro-ph.IM↗

arXiv2026

Multiwavelength Analysis of the Einstein Probe X-ray Transient EP240305a

We report multiwavelength observations of EP240305a, an uncatalogued X-ray transient detected by the Einstein Probe on March 5, 2024. The source exhibits distinct characteristics across the X-ray, optical, near-infrared, and radio bands. The soft X-ray observations show two significant flares lasting ~100-250 s, accompanied by rapid flux decay in a few days, and the optical and near-infrared data reveal a faint, candidate counterpart. In contrast, the radio observations expose a long-term spectral evolution from a self-absorbed to an optically thin state within two months, implying discrete jet ejection. We compare EP240305a with known classes of X-ray transients and find that it is unlikely to be associated with long-timescale transients such as jetted tidal disruption events or X-ray binaries. Its properties also disfavor a short-timescale stellar flare origin. Although the absence of optical spectroscopy prevents a redshift determination, the source exhibits properties similar to those of gamma-ray-dark gamma-ray burst-like transients, which may be associated with relativistic jets viewed off-axis or with choked jets. The discovery of EP240305a, along with other uncataloged transients detected by the Einstein Probe, underscores the scientific potential of highly sensitive X-ray survey telescopes and rapid-response multiwavelength follow-up observations in exploring the nature of atypical astronomical transients.

astro-ph.HE↗

arXiv2026

EP250827b/SN 2025wkm: An X-ray Flash-Supernova Powered by a Central Engine and Circumstellar Interaction

We present the discovery of EP250827b/SN 2025wkm, an X-ray Flash (XRF) discovered by the Einstein Probe (EP), accompanied by a broad-line Type Ic supernova (SN Ic-BL) at $z = 0.1194$. EP250827b possesses a prompt X-ray luminosity of $\sim 10^{45} \, \rm{erg \, s^{-1}}$, lasts over 1000 seconds, and has a peak energy $E_{\rm{p}} < 1.5$ keV at 90\% confidence. SN 2025wkm possesses a double-peaked optical light curve (LC), though its bolometric luminosity plateaus after its initial peak for $\sim 20$ days, consistent with a central engine injecting additional energy into the explosion. Its spectrum transitions from a blue to red continuum with clear blueshifted broad absorption features consistent with a SN Ic-BL classification. We do not detect any transient radio emission and rule out the existence of an on-axis, energetic jet $\gtrsim 10^{50}~$erg assuming a typical LGRB circumburst constant density ($n \approx 10^{-3}$--$10^{-1}~{\rm cm}^{-3}$) and microphysical parameters ($ε_{\rm e} = 0.1$ and $ε_{\rm B} = 0.01$). In the model we invoke, the collapse gives rise to a long-lived magnetar, potentially surrounded by an accretion disk. Magnetically--driven winds from the magnetar and the disk mix together and break out with a velocity $\sim 0.35c$ and interact with an extended circumstellar medium with radius $\sim 10^{13}$ cm, generating X-ray breakout emission through non-thermal free-free processes. The disk outflows and magnetar winds power blackbody photospheric emission as they cool adiabatically and thermalize, producing the first SN peak. The spin-down luminosity of the magnetar and radioactive decay of $^{56}$Ni powers the late-time emission. We end by discussing the landscape of XRF-SNe within the context of EP's recent discoveries.

astro-ph.HE↗

arXiv2026

Time-domain Radio-loudness of Active Galactic Nuclei: Intermittency, Memory, and Jet Escape

The classical radio-loudness parameter $R \equiv f_ν(5\,\mathrm{GHz})/f_ν(4400\,\textÅ)$ divides a radio flux density by an optical/UV accretion tracer, but the two terms do not probe the same clock. The radio numerator can blend compact-core emission from the current engine, lobe and relic plasma left by earlier jet episodes, and host-galaxy synchrotron emission. We introduce a time-domain radio-loudness (TDRL) description that keeps these contributions separate. The radio numerator is written as compact-core and extended-lobe terms, with recovered fractions set by observing frequency, angular resolution, and surface-brightness sensitivity. For a single intermittently jetted AGN population, a two-state duty cycle filtered by exponential lobe fading gives an exact stationary Beta distribution for the normalized extended-radio response. Its mean is $\fduty$, while its variance scales as $(1+χ_ν)^{-1}$, where $χ_ν\equiv\taunu/t_{\rm switch}$. In this reference limit, the familiar GHz valley near the classical radio-loud/radio-quiet boundary can arise from short radio memory alone, without requiring two intrinsic engine classes. Metre-wave surveys that recover diffuse emission and subtract the host contribution should therefore progressively fill the valley. In the $(\Rcore,\Rlobe)$ plane, a core--lobe mismatch index separates triggering, sustained, and remnant phases, provided orientation-dependent core beaming is modelled or controlled. A complementary two-barrier picture, involving horizon-threading magnetic flux and jet escape through the nuclear medium, separates jet launching from the formation of large-scale radio structure. This view makes radio loudness a probe of jet duty cycle, radio memory, and escape through the host environment.

astro-ph.GA↗