arXiv subjects

Yuanqi Liu

Publications and source records attributed to Yuanqi Liu.

At least 19 recordsLinked to original sources

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

Approximate maximum-likelihood decoding via truncated free energies

Maximum-likelihood decoding (MLD) achieves the minimum logical error rate of stabilizer codes under known i.i.d. Pauli noise, but its exact evaluation is \#P-hard. Practical pipelines therefore approximate MLD by minimum-weight decoding (MWD), retaining only the lowest-weight recovery per syndrome and discarding the coset degeneracy. The minimum-weight search is in turn implemented by stochastic solvers. We introduce approximate maximum-likelihood decoding (AMLD), a black-box framework that recycles the candidate samples discarded by stochastic inner decoders into a per-class truncated free-energy estimator. For every logical class represented in the candidate pool, the estimator is provably bounded below by the exact free energy and above by the empirical minimum weight. AMLD returns the logical class minimizing the estimated free energy with linear classical overhead. In SA-based Ising-decoder benchmarks, AMLD closes up to $83\%$ of the MWD--MLD threshold gap across the toric and color codes under bit-flip and depolarizing noise. The largest threshold improvement, from $17.28\%$ to $18.62\%$, occurs on the $6.6.6$ color code under depolarizing noise. We further demonstrate AMLD on the $[[144,12,12]]$ bivariate-bicycle code, whose bit-flip decoding problem has a hypergraph structure. This application requires neither matching-based enumeration nor code-specific tensor-network contraction. At $p=0.05$, AMLD reduces the logical error rate by $13\%$ relative to MWD evaluated on the same BP-OSD candidate pool.

quant-ph↗

arXiv2026

Real-time decoding of quantum error correction codes using high-performance computing

Quantum error correction (QEC) is indispensable for building scalable fault-tolerant quantum computers. Effective QEC demands stringent real-time decoding: the decoder must process syndrome measurements and determine corrections within a time scale--typically on the order of microseconds, to avoid data backlog. Scaling to large number of logical qubits further necessitates significant computational resources. In this work, we propose an architecture, called \emph{THQLink}, for real-time decoding of quantum error correction codes using high-performance computing (HPC) resources. The network connecting the HPC and the control system of quantum processing unit (QPU) is built on TH-Express and can be adapted to different quantum technologies and their associated control stacks. We report a round-trip latency of 2.944 $μ$s on average, with an incremental overhead of 130 ns per additional hop. Using a parallel window strategy, we demonstrate real-time decoding (1 $μ$s per QEC round) of the surface code up to distance 19 using a matching-based decoder on CPUs. Our work presents a scalable framework for real-time decoding in fault-tolerant quantum computing. It can be readily applied to quantum-centric supercomputers that feature tight integration between QPU and HPC resources, thereby enabling efficient support for hybrid quantum-classical algorithms and computation-intensive workloads offloaded from the QPU.

quant-ph↗

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

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

An iterative Ising decoder for quantum error correction codes

The Ising framework maps the decoding problem in quantum error correction onto ground-state optimization of a classical Hamiltonian, in which $X$-$Z$ error correlations enter as cross terms. Under phenomenological depolarizing noise, the exact joint formulation contains up to 8-body interactions for the toric code and 10-body for the $6.6.6$ color code. These high-order terms degrade solver convergence, inflate runtime, and raise the auxiliary spin overhead when embedding into native 2-body Ising hardware. In this work, we propose the iterative low-order decoding (ILOD) algorithm, which alternates between $X$- and $Z$-type sub-Hamiltonians, approximating cross-type correlations through Bayesian priors that reweight each type's couplings using the other type's inferred error configuration. This halves the maximum body count of interaction terms in the Hamiltonian, accelerating the solver, restoring convergence at larger code distances, and reducing the total spin count for 2-body embedding by a factor of $2.5$. For the toric code, ILOD attains a threshold of $4.73%$ versus $4.83%$ for the joint formulation, with the empirical runtime ratio scaling as $(0.81)^d$. For the $6.6.6$ color code, their thresholds agree within statistical uncertainty for small code distances, and ILOD remains convergent for larger distances where the joint formulation fails to converge despite a larger annealing budget.

quant-ph↗

arXiv2026

Synchrotron Self-Absorption Spectral Modeling Reveals a Magnetically Driven Shock-in-Jet Scenario in Blazar 1156+295

Unveiling the launching and driving mechanisms of powerful jets in active galactic nuclei (AGNs) is crucial for understanding the co-evolution of supermassive black holes (SMBHs) and their host galaxies. 1156+295 is a blazar at a redshift of z=0.729 and exhibits significant variability in long-term radio monitoring. Using multi-frequency Effelsberg single-dish flux density data from 2007 to 2012, we performed synchrotron self-absorption (SSA) spectral modeling and extracted the turnover frequency and turnover flux density. By combining SSA spectral modeling with the core size and brightness temperature from quasi-simultaneous very long baseline interferometry (VLBI) images, we estimated the jet magnetic-field strength and magnetic flux, and investigated their temporal evolution in 1156+295. The evolution of radio flux density, spectral shape, and jet structure is consistent with the shock-in-jet framework. The inferred magnetic flux reaching or exceeding the magnetically arrested disk (MAD) threshold, together with evidence that magnetic energy release precedes the radio flares, supports a magnetically driven jet scenario. Overall, our results place magnetic-field measurements, spectral evolution, and inner-jet structural changes on a common timeline, providing observational constraints on their coupled evolution during flares.

astro-ph.HE↗

arXiv2025

A pilot VLBI study of the SQUAB quasar sample featuring multiple Gaia detections

Our previous work identified a class of SDSS quasars exhibiting multiple Gaia detections, classifying them as candidates for various astrophysical systems such as quasar-star pairs, dual quasars, and gravitationally lensed quasars. In this paper, we present a pilot VLBI study targeting a radio-bright subsample and report the first high-resolution imaging results. By leveraging the milliarcsecond-scale resolution of VLBI and its precise astrometric coordination incorporating with Gaia, we aim to refine the classification of these multiple matched sources, search for potential dual AGNs, and assess the efficacy of the combined Gaia-VLBI approach in resolving ambiguous quasar systems. We cross-matched the SQUAB quasar sample with the FIRST and NVSS catalogs, identifying 18 radio-emitting sources. The three brightest were selected for dual-frequency (1.6 and 4.9 GHz) VLBA observations. We performed VLBI imaging at both Gaia positions, constructed spectral index maps, and estimated brightness temperatures to characterize the radio morphology and physical properties. For the three target sources, our VLBI observations reveal compact radio structures consistent with single AGN at the primary Gaia positions. No significant emission is detected at the secondary Gaia locations. These results support the interpretation of the sources as quasar$-$star pairs, in line with earlier studies. This pilot study demonstrates the value of radio-VLBI high-resolution follow-ups on Gaia-selected quasar systems with multiple counterparts, showing how they can unambiguously reveal the true nature of these systems and help remove contaminants from dual AGN candidate samples.

astro-ph.HE↗

arXiv2025

Discovery of giant bubbles in the hot gaseous halo of the massive disk galaxy NGC 6286

Based on archival Chandra X-ray observation, optical integral-field spectroscopic data and radio interferometric data, we report the discovery of a pair of giant bubbles (with a projected radius ~ 5 kpc) of ionized gas emerging from a highly inclined starburst galaxy NGC 6286, which is undergoing strong tidal interactions with its close neighbor NGC 6285. The bubbles are manifested by extraplanar soft X-ray emission with an X-shaped morphology, which is tightly co-spatial with $\rm Hα$ line emission and partially coincident with radio continuum. Low surface brightness diffuse X-ray emission can be traced out to ~ 90 kpc from the galactic center, revealing the presence of an extended hot gaseous halo. X-ray spectral analysis of the bubbles yields a gas temperature of $0.70^{+0.16}_{-0.18}$ keV, a relatively high value among known galactic-scale bubbles in the local universe. An average energy injection rate of ~ $10^{43}$ erg $\rm s^{-1}$ is required to inflate the bubbles within an estimated dynamical age of ~ 6.4 Myr. The multi-wavelength properties of the bubbles can be understood with the conventional superwind scenario, in which disk/halo gas is swept up into an expanding, cooling shell by a hot tenuous wind. The current starburst in NGC 6286 is energetically sufficient to launch the superwind, although we cannot rule out the possibility of a more violent AGN in the recent past as the driving source. Future high-resolution spectroscopic observations will help to shed light on the origin of the superwind and its role as an important galactic feedback process.

astro-ph.GA↗

arXiv2025

A Deep VLA Search for a Persistent Radio Counterpart to the One-off FRB 20250316A

Fast Radio Burst (FRB) 20250316A, detected by CHIME on 2025 March 16 with a fluence of $1.7\pm0.1~\mathrm{Jy\,ms}$ and a dispersion measure of $161.3\pm0.4~\mathrm{pc\,cm^{-3}}$, ranks among the brightest extragalactic FRBs at $\sim 40$ Mpc. We obtained deep Karl G. Jansky Very Large Array follow-up at 15~GHz on 2025 April 5 and 9 and find no persistent radio source (PRS). Our best image reaches an rms of $2.8~μ\mathrm{Jy\,beam^{-1}}$, yielding a $3σ$ upper limit of $<8.4~μ\mathrm{Jy}$ at the FRB position, corresponding to $νL_ν< 2.4\times10^{35}~\mathrm{erg\,s^{-1}}$. These results represent among the most stringent constraints for a non-repeating FRB, lying $\gtrsim 3$ orders of magnitude below the $νL_ν$ of compact persistent radio sources around well-studied repeaters, thereby disfavoring bright magnetar-nebula scenarios and pointing to low-density, weakly magnetized environments. Interpreting our limit through pulsar-/magnetar-wind synchrotron frameworks places joint constraints on ambient density and engine power. If the empirical PRS--rotation-measure trend reported for repeaters extends to one-off sources, our limit implies $\vert \mathrm{RM} \vert \lesssim 30~\mathrm{rad\,m^{-2}}$, consistent with a clean magneto-ionic sight line and progenitor channels such as neutron-star mergers or giant flares from older magnetars.

astro-ph.HE↗

arXiv2025

A Jetted Wandering Massive Black Hole Candidate in a Dwarf Galaxy

Wandering massive black holes (MBHs) are thought to form through gravitational recoil or galaxy mergers, but observational confirmation of their displacement in dwarf galaxies, critical laboratories for early-universe SMBH seeding, remains scarce. Using multi-epoch very long baseline interferometry (VLBI), we identify a displaced MBH in the dwarf galaxy MaNGA 12772-12704, located 0.94 kilo-parsec from its optical center. The source exhibits unambiguous signatures of an accreting MBH: a brightness temperature exceeding $10^9$K, a parsec-scale jet, and flux density variability over a 30-year baseline. This system provides the first robust evidence that dynamical black hole interactions predicted in hierarchical galaxy evolution occur even in low-mass hosts. The discovery challenges models requiring centralized gas reservoirs for MBH growth and directly informs high-redshift seeding scenarios.

astro-ph.GA↗

arXiv2025

Lunar Orbital VLBI Experiment: motivation, scientific purposes and status

The Lunar Orbital VLBI Experiment (LOVEX) is a scientific component of the Chinese Lunar Exploration Project (CLEP) Chang'E-7. The spaceborne component of LOVEX is implemented onboard the relay satellite QueQiao-2, which was launched on 2024 March 20, and later placed into an elliptical selenocentric orbit. The LOVEX-specific payload consists of an X-band cryogenic receiver, a hydrogen maser frequency standard, and VLBI data formatting and acquisition electronics. Several components of the QueQiao-2 nominal onboard instrumentation, such as the 4.2-meter antenna, the data storage device, and the downlink communication system, contribute to the overall spaceborne VLBI instrumentation. This allows us to form a space radio telescope capable of co-observing with Earth-based radio telescopes in VLBI mode. In this space VLBI system, the length of the baseline extends up to approximately 380,000 km. This paper presents the LOVEX scientific objectives, architecture, instrumentation, pre-launch tests, in-flight verification and calibration, and the first in-flight detections of interferometric response (''fringes'') achieved through observations of the quasar AO 0235+164 and the Chang'E-6 orbital module, positioned at the Sun-Earth Lagrange point L2. These initial results demonstrate the successful performance of LOVEX, verifying its capability for both astronomical and spacecraft tracking observations at ultra-long VLBI baselines.

astro-ph.IM↗

arXiv2025

High-redshift quasars at $z \geq 3$ -- III. Parsec-scale jet properties from VLBI observations

High redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z $\geq$ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35\% unresolved cores, 59\% core-jet structures, and only 6\% core-double jet morphology. Brightness temperatures are generally lower than expected for highly radiative sources. The jet proper motions are surprisingly slow compared to lower-redshift samples. We observe a high fraction of young and/or confined peak-spectrum sources, providing insights into early AGN evolution in dense environments during early cosmic epochs. The observed trends may reflect genuine evolutionary changes in AGN structure over cosmic time, or selection effects favoring more compact sources at higher redshifts. These results stress the complexity of high-redshift radio-loud AGN populations and emphasize the need for multi-wavelength, high-resolution observations to fully characterize their properties and evolution through cosmic history.

astro-ph.HE↗

arXiv2025

First Detection of Radio Emission from the Intermediate Mass Black Hole in POX 52: Deep Multi-Band Observations with ATCA and VLA

We present the first multi-band centimeter detection of POX 52, a nearby dwarf galaxy believed to habor a robust intermediate mass black hole (IMBH). We conducted the deep observations using the Australia Telescope Compact Array (ATCA), spanning frequencies from 4.5 to 10 GHz, as well as the sensitive observations from the Karl G. Jansky Very Large Array (VLA) operating in its most extended A-configuration at S band (2--4 GHz) and C band (4--8 GHz). In the ATCA observations, the source shows a compact morphology, with only one direction marginally resolved. The higher resolution of the VLA allowed us to slightly resolve the source, fitting it well with a two-dimensional Gaussian model. The detected radio emission confirms the presence of Active Galactic Nucleus (AGN) activity, indicating either a low-power jet or AGN-driven winds/outflows. Our dual-epoch observations with ATCA and VLA, together with previous non-detection flux density upper limits, reveal radio emission variability spanning two decades. In addition, we find that POX 52 aligns well with the low-mass extension of the fundamental plane for high-accretion, radio-quiet massive AGNs.

astro-ph.GA↗

arXiv2024

The RAdio Galaxy Environment Reference Survey (RAGERS): Evidence of an anisotropic distribution of submillimeter galaxies in the 4C 23.56 protocluster at z=2.48

High-redshift radio(-loud) galaxies (H$z$RGs) are massive galaxies with powerful radio-loud active galactic nuclei (AGNs) and serve as beacons for protocluster identification. However, the interplay between H$z$RGs and the large-scale environment remains unclear. To understand the connection between H$z$RGs and the surrounding obscured star formation, we investigated the overdensity and spatial distribution of submillimeter-bright galaxies (SMGs) in the field of 4C\,23.56, a well-known H$z$RG at $z=2.48$. We used SCUBA-2 data ($σ\,{\sim}\,0.6$\,mJy) to estimate the $850\,{\rm μm}$ source number counts and examine the radial and azimuthal overdensities of the $850\,{\rm μm}$ sources in the vicinity of the H$z$RG. The angular distribution of SMGs is inhomogeneous around the H$z$RG 4C\,23.56, with fewer sources oriented along the radio jet. We also find a significant overdensity of bright SMGs (${\rm S}_{850\rm\,μm}\geq5\,$mJy). Faint and bright SMGs exhibit different spatial distributions. The former are concentrated in the core region, while the latter prefer the outskirts of the H$z$RG field. High-resolution observations show that the seven brightest SMGs in our sample are intrinsically bright, suggesting that the overdensity of bright SMGs is less likely due to the source multiplicity.

astro-ph.GA↗

arXiv2024

VLBI observations of the high-redshift X-ray bright blazar SRGE J170245.3+130104

Aims. The X-ray luminous and radio-loud AGN SRGE J170245.3+130104 discovered at z $\sim$ 5.5 provides unique chances to probe the SMBH growth and evolution with powerful jets in the early Universe. Methods. We present 1.35 - 5.1 GHz Very Long Baseline Array (VLBA) results on the radio continuum emission and spectrum analysis for this quasar in a low flux density state. Results. This source is unresolved at three frequencies with the total flux densities of 8.35$\pm$0.09 mJy beam-1, 7.47$\pm$0.08 mJy beam-1, and 6.57$\pm$0.02 mJy beam-1 at 1.73 GHz, 2.26 GHz, and 4.87 GHz, respectively. Meanwhile, the brightness temperature is higher than 109 K. Conclusions. Compared with previous radio observations with arcsec-scale resolution, nearly all the radio emission from this source concentrates in the very central milli-arcsecond (mas) scale area. We confirm this source is a bright blazar at z > 5. This young AGN provide us the great chances to understand the first generation of strong jets in the early Universe.

astro-ph.GA↗

arXiv2024

Diverse molecular gas excitations in quasar host galaxies at z \sim 6

We present observations using the NOrthern Extended Millimetre Array (NOEMA) of CO and $\rm H_{2}O$ emission lines, and the underlying dust continuum in two quasars at $z \sim 6$, i.e., P215-16 at $z$ = 5.78 and J1429+5447 at $z$ = 6.18. Notably, among all published CO SLEDs of quasars at $z \sim 6$, the two systems reveal the highest and the lowest CO level of excitation, respectively. Our radiative transfer modeling of the CO SLED of P215-16 suggests that the molecular gas heated by AGN could be a plausible origin for the high CO excitation. For J1429+5447, we obtain the first well-sampled CO SLED (from transitions from 2-1 to 10-9) of a radio-loud quasar at $z\gtrsim 6$. Analysis of the CO SLED suggests that a single photo-dissociation region (PDR) component could explain the CO excitation in the radio-loud quasar J1429+5447. This work highlights the utility of the CO SLED in uncovering the ISM properties in these young quasar-starburst systems at the highest redshift. The diversity of the CO SLEDs reveals the complexities in gas conditions and excitation mechanisms at their early evolutionary stage.

astro-ph.GA↗

arXiv2022

Is the X-ray bright z = 5.5 quasar SRGE J170245.3+130104 a blazar?

Jets may have contributed to promoting the growth of seed black holes in the early Universe, and thus observations of radio-loud high-redshift quasars are crucial to understanding the growth and evolution of the early supermassive black holes. Here we report the radio properties of an X-ray bright $z=5.5$ quasar, SRGE J170245.3+130104 (J1702+1301). Our high-resolution radio images reveal the radio counterpart at the optical position of J1702+1301, while another radio component is also detected at $\sim$23.5\arcsec\ to the southwest. Our analysis suggests that this southwest component is associated with a foreground galaxy at $z\approx 0.677$, which is mixed with J1702+1301 in low-frequency low-resolution radio images. After removing the contamination from this foreground source, we recalculated the radio loudness of J1702+1301 to be $R>$1100, consistent with those of blazars. J1702+1301 exhibits a flat radio spectrum ($α= -0.17 \pm 0.05$, $S \propto ν^α$) between 0.15 and 5 GHz; above 5 GHz, it shows a rising spectrum shape, and the spectral index $α^{8.2}_{4.7}$ appears to be correlated with the variation of the flux density: in burst states, $α^{8.2}_{4.7}$ becomes larger. J1702+1301 displays distinct radio variability on timescales from weeks to years in the source's rest frame. These radio properties, including high radio loudness, rising spectrum, and rapid variability, tend to support it as a blazar.

astro-ph.HE↗