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Youling Yue

Publications and source records attributed to Youling Yue.

At least 19 recordsLinked to original sources
arXiv2026

Probing Variations in Earth's Ionosphere Using Pulsars

We present high cadence 10-minute rotation measure (RM) monitoring of PSR~J0814+7429 using the LOw-Frequency ARray, aiming to probe ionospheric variability along the pulsar line of sight (LoS). By separating the ionospheric contribution from the observed RM, we quantitatively reconstruct the diurnal variation of the ionospheric electron density along the pulsar LoS based on the World Magnetic Model. The derived variations exhibit clear solar-driven modulation, including the ionospheric noontime bite-out phenomenon, and show good agreement with the LoS total electron content reconstructed from independent global vertical total electron content maps. These results demonstrate the feasibility of using pulsars as probes of temporal variations in the electron density of the Earth's ionosphere.

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arXiv2026

Pulsar Backend for 21 CentiMeter Array: Implementation of Data Acquisition and Initial Results

We implemented a data acquisition system for 21 CentiMeter Array (21CMA), enabling baseband observations targeting pulsars and fast radio bursts. Based on the Radio Frequency System-on-Chip (RFSoC) platform, the new backend is capable of instantaneously covering the effective bandwidth from 50 to 350 MHz, with multi-board synchronization achieved at the timescale of the sampling clock. We observed PSR B0329+54 with a single station to verify the signal path integrity; then solved phase relations of multiple station pairs using bright persistent radio sources like Cas A and Cyg A; using these phase solutions, a multiple-station coherently beamformed observation of PSR B0329+54 was carried out, showing a signal-to-noise ratio of 699.09 for a 2.5-hour observation with eight stations, opening up a possibility of tied-array low-frequency pulsar observations on 21CMA.

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arXiv2026

Improved proper motion and gravity tests with PSR J1913+1102

PSR J1913+1102 is a highly asymmetric double neutron star system and an excellent laboratory for testing scalar-tensor gravity theories, as well as a potential progenitor analogue of GW170817 that will merge in 470 Myr. We present an updated timing analysis combining 13 years of historical Arecibo observations and new FAST measurements, using two approaches to model dispersion-measure variations. The new timing solution provides precise measurements of four post-Keplerian parameters and improves the system mass estimates. Assuming general relativity and modelling the DM variation with a Gaussian process, we obtain a three-fold improvement in the total mass, m_{tot}=2.88948(20) M_\odot, and nearly four-fold improvements in the pulsar and companion masses, m_p=1.599(8) M_\odot and m_c=1.290(8) M_\odot, giving the mass ratio, q=0.807(8). We also measure an improved proper motion, \mu=7.71(25) mas yr^{-1}, enabling a more accurate correction of the observed orbital-period derivative. Combined with the improved orbital-decay measurement, this yields an intrinsic orbital-period derivative \dot{P}_b^{intr}=-4.60(6)\times10^{-13} s s^{-1}, five times more precise than the previous value and fully consistent with the general-relativistic prediction for gravitational-wave damping. The improved masses and precise \dot{P}*b^{intr} place stringent constraints on dipolar gravitational-wave emission and the spontaneous-scalarisation window around 1.6 M*\odot. The refined proper motion and mass measurements also provide tighter constraints on the final helium-star mass immediately prior to its core collapse and formation of the second NS in a supernova, as well as on the magnitude and direction of the associated natal kick of the DNS system.

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arXiv2026

Pulsar scintillation studies with LOFAR III. Annual variations in PSR~J0814$+$7429

The interstellar scintillation observed in radio pulsars arises from interference between electromagnetic waves scattered by electron density fluctuations in the turbulent interstellar plasma, providing a critical tool for probing the small-scale structure of the ionized interstellar medium and the pulsar system itself. The primary aim of this work is to study long-term scintillation variations for a bright and nearby pulsar, PSR J0814$+$7429, carried out from 2013 September to 2023 September with the LOw-Frequency ARray (LOFAR) High Band Antennae in the frequency range of 120 - 170 MHz. We derive the basic scintillation parameters, scintillation bandwidth ($\Delta\nu_{\rm d}$) and scintillation timescale ($\Delta\tau_{\rm d}$), from the two-dimensional (2D) auto-covariance function of the dynamic spectra that are a 2D matrix of pulse intensity as a function of time and frequency. We present the long-term monitoring of $\Delta\nu_{\rm d}$ and $\Delta\tau_{\rm d}$ for PSR J0814$+7429$, which shows a strong annual variation in the time series of the $\Delta\tau_{\rm d}$. From our modeling of the annual variations of scintillation velocities, the scattering screen is anisotropic and located at $0.23\pm0.02$ kpc from the Earth, likely corresponding to the boundary of the Local Bubble.

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arXiv2025

Improving pulsar search efficiency in next-generation pulsar surveys with artificial intelligence

Pulsar searching with next-generation radio telescopes requires efficiently sifting through millions of candidates generated by search pipelines to identify the most promising ones. This challenge has motivated the utilization of Artificial Intelligence (AI)-based tools. In this work, we explore an optimized pulsar search pipeline that utilizes deep learning to sift ``snapshot'' candidates generated by folding de-dispersed time series data. This approach significantly accelerates the search process by reducing the time spent on the folding step. We also developed a script to generate simulated pulsars for benchmarking and model fine-tuning. The benchmark analysis used the NGC 5904 globular cluster data and simulated pulsar data, showing that our pipeline reduces candidate folding time by a factor of $\sim$10 and achieves 100% recall by recovering all known detectable pulsars in the restricted parameter space. We also tested the speed-up using data of known pulsars from a single observation in the Southern-sky MWA Rapid Two-metre (SMART) survey, achieving a conservatively estimated speed-up factor of 60 in the folding step over a large parameter space. We tested the model's ability to classify pulsar candidates using real data collected from the FAST, GBT, MWA, Arecibo, and Parkes, demonstrating that our method can be generalized to different telescopes. The results show that the optimized pipeline identifies pulsars with an accuracy of 0.983 and a recall of 0.9844 on the real dataset. This approach can be used to improve the processing efficiency for the SMART and is also relevant for future SKA pulsar surveys.

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arXiv2025

The Chinese pulsar timing array data release I. Polarimetry for 56 millisecond pulsars

We present polarization pulse profiles for 56 millisecond pulsars (MSPs) monitored by the Chinese Pulsar Timing Array (CPTA) collaboration using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The observations centered at 1.25 GHz with a raw bandwidth of 500 MHz. Due to the high sensitivity ($\sim$16 K/Jy) of the FAST telescope and our long integration time, the high signal-to-noise ratio polarization profiles show features hardly detected before. Among 56 pulsars, the polarization profiles of PSRs J0406$+$3039, J1327$+$3423, and J2022$+$2534 were not previously reported. 80\% of MSPs in the sample show weak components below 3\% of peak flux, 25\% of pulsars show interpulse-like structures, and most pulsars show linear polarization position angle jumps. Six pulsars seem to be emitting for full rotation phase, with another thirteen pulsars being good candidates for such a 360$^\circ$ radiator. We find that the distribution of the polarization percentage in our sample is compatible with the normal pulsar distribution. Our detailed evaluation of the MSP polarization properties suggests that the wave propagation effects in the pulsar magnetosphere are important in shaping the MSP polarization pulse profiles.

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arXiv2023

X-ray hardening preceding the onset of SGR 1935+2154's radio pulsar phase

Magnetars are neutron stars with extremely strong magnetic fields, frequently powering high-energy activity in X-rays. Pulsed radio emission following some X-ray outbursts have been detected (\citealt{Camilo2006,camilo2007a}), albeit its physical origin is unclear. It has long been speculated that the origin of magnetars' radio signals is different from those from canonical pulsars, although convincing evidence is still lacking. Five months after magnetar SGR 1935+2154's X-ray outburst and its associated Fast Radio Burst (FRB) 20200428, a radio pulsar phase was discovered. Here we report the discovery of X-ray spectral hardening associated with the emergence of periodic radio pulsations from SGR 1935+2154 and a detailed analysis of the properties of the radio pulses. The observations suggest that radio emission originates from the outer magnetosphere of the magnetar, and the surface heating due to the bombardment of inward-going particles from the radio emission region is responsible for the observed X-ray spectral hardening.

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arXiv2023

A radio pulsar phase from SGR J1935+2154 provides clues to the magnetar FRB mechanism

The megajansky radio burst, FRB 20200428, and other bright radio bursts detected from the Galactic source SGR J1935+2154 suggest that magnetars can make fast radio bursts (FRBs), but the emission site and mechanism of FRB-like bursts are still unidentified. Here we report the emergence of a radio pulsar phase of the magnetar five months after FRB 20200428. 795 pulses were detected in 16.5 hours over 13 days by the Five-hundred-meter Aperture Spherical Radio telescope, with luminosities about eight decades fainter than FRB 20200428. The pulses were emitted in a narrow phase window anti-aligned with the X-ray pulsation profile observed by the X-ray telescopes. The bursts, conversely, appear in random phases. This dichotomy suggests that radio pulses originate from a fixed region within the magnetosphere, but bursts occur in random locations and are possibly associated with explosive events in a dynamically evolving magnetosphere. This picture reconciles the lack of periodicity in cosmological repeating FRBs within the magnetar engine model.

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arXiv2023

Categorize Radio Interference using component and temporal analysis

Radio frequency interference (RFI) is a significant challenge faced by today's radio astronomers. While most past efforts were devoted to cleaning the RFI from the data, we develop a novel method for categorizing and cataloguing RFI for forensic purpose. We present a classifier that categorizes RFI into different types based on features extracted using Principal Component Analysis (PCA) and Fourier analysis. The classifier can identify narrowband non-periodic RFI above 2 sigma, narrowband periodic RFI above 3 sigma, and wideband impulsive RFI above 5 sigma with F1 scores between 0.87 and 0.91 in simulation. This classifier could be used to identify the sources of RFI as well as to clean RFI contamination (particularly in pulsar search). In the long-term analysis of the categorized RFI, we found a special type of drifting periodic RFI that is detrimental to pulsar search. We also found evidences of an increased rate of impulsive RFI when the telescope is pointing toward the cities. These results demonstrate this classifier's potential as a forensic tool for RFI environment monitoring of radio telescopes.

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arXiv2022

Frequency-dependent polarization of repeating fast radio bursts-implications for their origin

The polarization of fast radio bursts (FRBs), bright astronomical transients, contains crucial information about their environments. We report polarization measurements of five repeating FRBs, the abundant signals of which enable wide-band observations with two telescopes. A clear trend of lower polarization at lower frequencies was found, which can be well characterized by a single parameter rotation-measure-scatter (σRM) and modeled by multi-path scatter. Sources with higher σRM have higher RM magnitude and scattering timescales. The two sources with the most substantial σRM, FRB 20121102A and FRB 20190520B, are associated with a compact persistent radio source. These properties indicate a complex environment near the repeating FRBs, such as a supernova remnant or a pulsar wind nebula, consistent with their arising from young populations.

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arXiv2021

An Early Transition to Magnetic Supercriticality in Star Formation

Magnetic fields play an important role in the evolution of interstellar medium and star formation. As the only direct probe of interstellar field strength, credible Zeeman measurements remain sparse due to the lack of suitable Zeeman probes, particularly for cold, molecular gas. Here we report the detection of a magnetic field of $+$3.8 $\pm$ 0.3 $μ$G through the HI narrow self-absorption (HINSA) toward L1544, a well-studied prototypical prestellar core in an early transition between starless and protostellar phases characterized by high central number density and low central temperature. A combined analysis of the Zeeman measurements of quasar HI absorption, HI emission, OH emission, and HINSA reveals a coherent magnetic field from the atomic cold neutral medium (CNM) to the molecular envelope. The molecular envelope traced by HINSA is found to be magnetically supercritical, with a field strength comparable to that of the surrounding diffuse, magnetically subcritical CNM despite a large increase in density. The reduction of the magnetic flux relative to the mass, necessary for star formation, thus seems to have already happened during the transition from the diffuse CNM to the molecular gas traced by HINSA, earlier than envisioned in the classical picture where magnetically supercritical cores capable of collapsing into stars form out of magnetically subcritical envelopes.

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arXiv2021

A GPU based single-pulse search pipeline (GSP) with database and its application to the commensal radio astronomy FAST survey (CRAFTS)

We developed a GPU based single-pulse search pipeline (GSP) with candidate-archiving database. Largely based upon the infrastructure of Open source pulsar search and analysis toolkit (PRESTO), GSP implements GPU acceleration of the de-dispersion and integrates a candidate-archiving database. We applied GSP to the data streams from the commensal radio astronomy FAST survey (CRAFTS), which resulted in a quasi-real-time processing. The integrated candidate database facilitates synergistic usage of multiple machine-learning tools and thus improves efficient identification of radio pulsars such as rotating radio transients (RRATs) and Fast Radio Bursts (FRBs). We first tested GSP on pilot CRAFTS observations with the FAST Ultra-Wide Band (UWB) receiver. GSP detected all pulsars known from the the Parkes multibeam pulsar survey in the respective sky area covered by the FAST-UWB. GSP also discovered 13 new pulsars. We measured the computational efficiency of GSP to be ~120 times faster than the original PRESTO and ~60 times faster than a MPI-parallelized version of PRESTO.

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arXiv2021

FAST discovery of an extremely radio-faint millisecond pulsar from the Fermi-LAT unassociated source 3FGL J0318.1+0252

High sensitivity radio searches of unassociated $γ$-ray sources have proven to be an effective way of finding new pulsars. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during its commissioning phase, we have carried out a number of targeted deep searches of \textit{Fermi} Large Area Telescope (LAT) $γ$-ray sources. On Feb. 27$^{th}$, 2018 we discovered an isolated millisecond pulsar (MSP), PSR J0318+0253, coincident with the unassociated $γ$-ray source 3FGL J0318.1+0252. PSR J0318+0253 has a spin period of $5.19$ milliseconds, a dispersion measure (DM) of $26$ pc cm$^{-3}$ corresponding to a DM distance of about $1.3$ kpc, and a period-averaged flux density of $\sim$11 $\pm$ 2 $μ$Jy at L-band (1.05-1.45 GHz). Among all high energy MSPs, PSR J0318+0253 is the faintest ever detected in radio bands, by a factor of at least $\sim$4 in terms of L-band fluxes. With the aid of the radio ephemeris, an analysis of 9.6 years of \textit{Fermi}-LAT data revealed that PSR J0318+0253 also displays strong $γ$-ray pulsations. Follow-up observations carried out by both Arecibo and FAST suggest a likely spectral turn-over around 350 MHz. This is the first result from the collaboration between FAST and the \textit{Fermi}-LAT teams as well as the first confirmed new MSP discovery by FAST, raising hopes for the detection of many more MSPs. Such discoveries will make a significant contribution to our understanding of the neutron star zoo while potentially contributing to the future detection of gravitational waves, via pulsar timing array (PTA) experiments.

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arXiv2021

CRAFTS for Fast Radio Bursts Extending the dispersion-fluence relation with new FRBs detected by FAST

We report three new FRBs discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), namely FRB 181017.J0036+11, FRB 181118 and FRB 181130, through the Commensal Radio Astronomy FAST Survey (CRAFTS). Together with FRB 181123 that was reported earlier, all four FAST-discovered FRBs share the same characteristics of low fluence ($\leq$0.2 Jy ms) and high dispersion measure (DM, $>1000$ \dmu), consistent with the anti-correlation between DM and fluence of the entire FRB population. FRB 181118 and FRB 181130 exhibit band-limited features. FRB 181130 is prominently scattered ($τ_s\simeq8$ ms) at 1.25 GHz. FRB 181017.J0036+11 has full-bandwidth emission with a fluence of 0.042 Jy ms, which is one of the faintest FRB sources detected so far. CRAFTS starts to built a new sample of FRBs that fills the region for more distant and fainter FRBs in the fluence-$\rm DM_E$ diagram, previously out of reach of other surveys. The implied all sky event rate of FRBs is $1.24^{+1.94}_{-0.90} \times 10^5$ sky$^{-1}$ day$^{-1}$ at the $95\%$ confidence interval above 0.0146 Jy ms. We also demonstrate here that the probability density function of CRAFTS FRB detections is sensitive to the assumed intrinsic FRB luminosity function and cosmological evolution, which may be further constrained with more discoveries.

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arXiv2020

A single pulse study of PSR J1022+1001

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we have recorded 10^5 single pulses from PSR J1022+1001. We studied the polarization properties, their energy distribution and their times of arrival. This is only possible with the high sensitivity available using FAST. There is no indication that PSR~J1022+1001 exhibits giant pulse, nulling or traditional mode changing phenomena. The energy in the leading and trailing components of the integrated profile is shown to be correlated. The degree of both linear and circular polarization increases with the pulse flux density for individual pulses. Our data indicates that pulse jitter leads to an excess noise in the timing residuals of 67 ns when scaled to one hour, which is consistent with Liu et al. (2015). We have unsuccessfully trialled various methods to improve timing precision through the selection of specific single pulses. Our work demonstrates that FAST can detect individual pulses from pulsars that are observed in order to detect and study gravitational waves. This capability enables detailed studies, and parameterisation, of the noise processes that affect the sensitivity of a pulsar timing array.

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arXiv2020

A Fast Radio Burst discovered in FAST drift scan survey

We report the discovery of a highly dispersed fast radio burst, FRB~181123, from an analysis of $\sim$1500~hr of drift-scan survey data taken using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulse has three distinct emission components, which vary with frequency across our 1.0--1.5~GHz observing band. We measure the peak flux density to be $>0.065$~Jy and the corresponding fluence $>0.2$~Jy~ms. Based on the observed dispersion measure of 1812~cm$^{-3}$~pc, we infer a redshift of $\sim 1.9$. From this, we estimate the peak luminosity and isotropic energy to be $\lesssim 2\times10^{43}$~erg~s$^{-1}$ and $\lesssim 2\times10^{40}$~erg, respectively. With only one FRB from the survey detected so far, our constraints on the event rate are limited. We derive a 95\% confidence lower limit for the event rate of 900 FRBs per day for FRBs with fluences $>0.025$~Jy~ms. We performed follow-up observations of the source with FAST for four hours and have not found a repeated burst. We discuss the implications of this discovery for our understanding of the physical mechanisms of FRBs.

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arXiv2020

Opportunities to Search for Extra-Terrestrial Intelligence with the Five-hundred-meter Aperture Spherical radio Telescope

The discovery of ubiquitous habitable extrasolar planets, combined with revolutionary advances in instrumentation and observational capabilities, has ushered in a renaissance in the search for extra-terrestrial intelligence (SETI). Large scale SETI activities are now underway at numerous international facilities. The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest single-aperture radio telescope in the world, well positioned to conduct sensitive searches for radio emission indicative of exo-intelligence. SETI is one of the five key science goals specified in the original FAST project plan. A collaboration with the Breakthrough Listen Initiative has been initiated in 2016 with a joint statement signed both by Dr. Jun Yan, the then director of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC), and Dr. Peter Worden, the Chairman of the Breakthrough Prize Foundation. In this paper, we highlight some of the unique features of FAST that will allow for novel SETI observations. We identify and describe three different signal types indicative of a technological source, namely, narrow-band, wide-band artificially dispersed, and modulated signals. We here propose observations with FAST to achieve sensitivities never before explored.

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