This paper presents the CosmicWeb-21cm array, a novel radio interferometer designed to overcome the key challenges in 21 cm cosmology. Its core innovations include: (1) a multi-scale nested geometry combining a hexagonal core with logarithmic spiral arms for excellent UV coverage and calibration robustness; (2) an intelligent non-uniform frequency sampling strategy that adapts resolution to foreground and signal characteristics, reducing data volume while preserving information; and (3) a machine-learning-enhanced, physics-informed processing pipeline that achieves 99.7% foreground removal efficiency; (4) a dual-polarization crossed dipole integrated with a dielectric lens and cryogenically cooled LNA, achieving stable beam patterns and low noise temperature (<35 K) across 50-250 MHz. These co-designed advances enable high sensitivity mapping of the Epoch of Reionization, dark energy constraints and cosmic-web structure.

Pulsar scintillation observations have revealed ubiquitous discrete scintillation screens in the interstellar medium. A major obstacle in identifying the nature of these screens is the uncertainty in their distances, which prevents precise correlation with known structures in the Milky Way. We used the Five-hundred-meter Aperture Spherical radio Telescope to observe PSR B1237+25, PSR 1842+14, and PSR 2021+51. We detected 10 scintillation arcs in PSR B1237+25, 1 in PSR 1842+14, and at least 6 in PSR 2021+51. By modeling the annual modulation of these scintillation arcs, we constrained the distances of the scintillation screens, as well as the anisotropic scattering directions and the projected velocities in those directions. The scintillation screens are distributed throughout the entire paths between Earth and the pulsars. Among these, the distance to the main scintillation screen toward PSR B1237+25 is 267-28+32 pc, the scintillation screen toward PSR B1842+14 is at a distance of 240-120+210 pc, and the main scintillation screen toward PSR B2021+51 is located at 887-132+167 pc. Several screens in our sample appear at distances coinciding with the Local Bubble boundary, particularly the brightest scintillation arc toward PSR B1237+25. We provide a substantial sample of scintillation screen measurements, revealing the rich plasma density fluctuation structures present in the Milky Way.

The radiative mechanism of coherent radio emission has remained an enigma since the discovery of pulsars, even the emergence of fast radio bursts (FRBs), which exhibit similarities to the single-pulse behavior of pulsars and have opened a new view for deciphering the long-standing mystery. Besides tremendous efforts in modelling, advanced facilities matter for solving the problem. The authors review the observational breakthroughs from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), which are providing pivotal insights to unravel the underlying physics of pulsars and FRBs. This study offers a novel perspective in the era when pulsars meet FRBs, and further investigations are encouraged to utilize the highly sensitive telescope, the FAST.

The Chinese Pulsar Timing Array (CPTA) has collected observations from 57 millisecond pulsars using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) for close to three years, for the purpose of searching for gravitational waves (GWs). To robustly search for ultra-low-frequency GWs, pulsar timing arrays (PTAs) need to use models to describe the noise from the individual pulsars. We report on the results from the single pulsar noise analysis of the CPTA data release I (DR1). Conventionally, power laws in the frequency domain are used to describe pulsar red noise and dispersion measurement (DM) variations over time. Employing Bayesian methods, we found the choice of number and range of frequency bins with the highest evidence for each pulsar individually. A comparison between a dataset using DM piecewise measured (DMX) values and a power-law Gaussian process to describe the DM variations shows strong Bayesian evidence in favour of the power-law model. Furthermore, we demonstrate that the constraints obtained from four independent software packages are very consistent with each other. The short time span of the CPTA DR1, paired with the large sensitivity of FAST, has proved to be a challenge for the conventional noise model using a power law. This mainly shows in the difficulty to separate different noise terms due to their covariances with each other. Nineteen pulsars are found to display covariances between the short-term white noise and long-term red and DM noise. With future CPTA datasets, we expect that the degeneracy can be broken. Finally, we compared the CPTA DR1 results against the noise properties found by other PTA collaborations. While we can see broad agreement, there is some tension between different PTA datasets for some of the overlapping pulsars. This could be due to the differences in the methods used to obtain the constraints or the different frequency range that is probed with the CPTA DR1, which probes a higher frequency range compared to the other PTAs.

In this paper, we present the linear decomposition method (LDM), which we developed to detect and analyze pulsar profile variations and mode-changing behavior. We developed LDM utilizing the likelihood function approach assuming the Gaussian noise. The LDM projects pulse profiles onto significance-ordered orthonormal vector bases. We show that the method is similar to the principal component analysis, but the LDM can handle more general situations. We use a simulated data set and data from the Kunming 40 m radio telescope to demonstrate the application of the LDM. We found that the LDM successfully identified mode changes for well-known mode-changing PSR B0329+54 and found a continuous pulse profile evolution for PSR B0355+54. We also show that the LDM can be used to improve the timing precision for mode-changing PSR B0329+54.

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 (∼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^∘ 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.

Fast Radio Bursts (FRBs) are enigmatic millisecond-duration radio transients of extra-galactic origin, whose underlying mechanisms and progenitors remain poorly understood. FRBs are broadly classified into two categories: repeating FRBs, which emit multiple bursts over time, and one-off FRBs, which are detected as single events. A central question in FRB research is whether these two classes share a common origin. In this study, we present observations of FRB 20240114A, a repeating FRB that entered a hyperactive phase in 2024 January. We conducted a 318 hr monitoring campaign using the Kunming 40-Meter Radio Telescope (KM40M) in the S-band (2.187-2.311 GHz), during which we detected eight radio bursts. We analyzed their properties, including dispersion measure, bandwidth, pulse width, flux, fluence, and energy. Additionally, we searched for counterparts in overlapping data from the Five-hundred-meter Aperture Spherical Telescope (FAST) in the L-band (1.0-1.5 GHz). While no bursts were temporally aligned between the two telescopes, we identified one FAST burst that arrived approximately 6 ms after one of the KM40M bursts. The absence of FAST counterparts for the KM40M bursts suggests that individual bursts from FRB 20240114A are likely narrow-band, with fractional bandwidths less than 10%. By comparing the cumulative event rates from KM40M and FAST observations, we found that the two measurements are compatible, indicating a possible flattening of the event rate at higher energies. This feature aligns with observations of one-off FRBs, supporting the hypothesis that repeating and one-off FRBs may share a common origin.

We present the scintillation velocity measurements of FRB~20201124A from the FAST observations, which reveal an annual variation. This annual variation is further supported by changes detected in the scintillation arc as observed from the secondary spectrum. We attribute the annual velocity variation to the presence of a moderately anisotropic scattering screen located at a distance of 0.4$\pm$0.1~kpc from Earth. Our results prove that the scintillation of this FRB is mainly caused by material close to Earth on a Galactic scale. However, scintillation observations of other FRBs may expose their surrounding environment or uncover possible orbital motion if scintillation is caused by materials in their host galaxy.

An observation control system is the foundation to support automatic observations by any radio telescope.Traditional observation control systems are usually coded using a compiled language,which is of higher efficiency compared with interpreted languages.Indeed,observation control systems are usually programmed using the C or C++languages.However,the high execution efficiency of C/C++is at the cost of a long development cycle,which is not only time consuming but also requires considerable skills for the developers.The development of computer hardware performance,as well as the optimization of the just-in-time compiler for new interpreted languages such as Python,provides a good balance between execution and development efficiency.In this paper,we introduce the observation control system developed for the Kunming 40-meter radio telescope run by Yunnan Observatories,Chinese Academy of Sciences.The system is developed mainly with the Python language,and we have optimized computationally intensive components with C++.We demonstrate that it is possible to achieve the required functionality and control precision with such a Python-C++programming paradigm.The performance of the control system is also assessed in this paper,demonstrating that satisfactory pointing accuracy and user experience can be attained.

Studying the universe through radio telescope observation is crucial. However, radio telescopes capture not only signals from the universe but also various interfering signals, known as Radio Frequency Interference (RFI). The presence of RFI can significantly impact data analysis. Ensuring the accuracy, reliability, and scientific integrity of research findings by detecting and mitigating or eliminating RFI in observational data, presents a persistent challenge in radio astronomy. In this study, we proposed a novel deep learning model called EMSCA-UNet for RFI detection. The model employs multi-scale convolutional operations to extract RFI features of various scale sizes. Additionally, an attention mechanism is utilized to assign different weights to the extracted RFI feature maps, enabling the model to focus on vital features for RFI detection. We evaluated the performance of the model using real data observed from the 40-meter radio telescope at Yunnan Observatory. Furthermore, we compared our results to other models, including U-Net, RFI-Net, and R-Net, using four commonly employed evaluation metrics: precision, recall, F1 score, and IoU. The results demonstrate that our model outperforms the other models on all evaluation metrics, achieving an average improvement of approximately 5\% compared to U-Net. Our model not only enhances the accuracy and comprehensiveness of RFI detection but also provides more detailed edge detection while minimizing the loss of useful signals.

n observation control system is the foundation to support automatic observations by any radio telescope. Traditional observation control systems are usually coded using a compiled language, which is of higher efficiency compared with interpreted languages. Indeed, observation control systems are usually programmed using the C or C++ languages. However, the high execution efficiency of C/C++ is at the cost of a long development cycle, which is not only time consuming but also requires considerable skills for the developers. The development of computer hardware performance, as well as the optimization of the just-in-time compiler for new interpreted languages such as Python, provides a good balance between execution and development efficiency. In this paper, we introduce the observation control system developed for the Kunming 40-meter radio telescope run by Yunnan Observatories, Chinese Academy of Sciences. The system is developed mainly with the Python language, and we have optimized computationally intensive components with C++. We demonstrate that it is possible to achieve the required functionality and control precision with such a Python-C++ programming paradigm. The performance of the control system is also assessed in this paper, demonstrating that satisfactory pointing accuracy and user experience can be attained.

We investigate changes in the shape of the averaged pulse profile in PSR B0355+54 (PSR J0358+5413) based on data obtained at the center frequency of 1250 MHz using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Our dataset consists of 12 non-consecutive observations, each lasting between 1 and 2 h. Considerable variation is observed in the averaged profiles across the observations even though each is folded from thousands of single pulses. Changes in the profile are measured through the ratio (R) between the peak intensities of the leading and trailing components. We find that the averaged pulse profile exhibits significant variation across observations, but distinctive from typical profile mode-changing. By dividing the frequency bandwidth into eight sub-bands, we demonstrate that the shape of the averaged profile undergoes significant evolution with frequency. In general, the changes in R across the sub-bands are different in different observations, but its value is uniform at low frequencies implying a more consistent emission. We demonstrate that the profile stabilization timescale for this pulsar is much longer than commonly suggested for ordinary pulsars, which is likely due to non-uniform and varying arrangement of the emission sources in the emission region.

We have carried out a detailed study of individual pulse emission from the pulsar J1741-0840 (B1738-08) observed using the Parkes and Effelsberg radio telescopes at the L band. The pulsar exhibits four emission components, which are not well resolved by employing multicomponent Gaussian fitting. The radio emission originates at a height of approximately 1000 km, with the viewing geometry characterized by inclination and impact angles roughly estimated at 81 degrees and 3 degrees, respectively. Fluctuation spectral analysis of single pulse behavior reveals two prominent periodicities, around 32 and five rotation periods. The longer periodic modulation feature is linked to nulling behavior across the entire emission window, with an updated nulling fraction of 23% +/- 2% derived from pulse energy distribution via Gaussian mixture modeling. In addition to quasiperiodic nulling, the pulsar also exhibits the presence of subpulse drifting in the trailing component, with the shorter periodic feature in the fluctuation spectra related to the phenomenon of subpulse drifting, and the longitudinal separation estimated to be about 5 degrees. Both periodic modulations show significant temporal evolution with time-dependent fluctuation power. The implications of understanding the radio emission mechanisms are discussed.

ABSTRACT Scintillation phenomena of pulsars provide an important tool for studying interstellar scattering screens and their properties. In this paper, we report pulsar scintillation phenomena of the PSR J0835−4510 at multiple epochs between MJD 58592 and MJD 58843 using the Kunming 40 m radio telescope at a centre frequency of 6656 MHz. We have measured the dynamic spectrum, and derived the scintillation time, bandwidth, and secondary spectrum at each observation epoch. For the first time, we report the detection of parabolic arc structure in the secondary spectra of PSR J0835−4510. Parabolic arcs with varying curvatures appear at all our observation epochs. We used both anisotropic and isotropic scattering screen models to fit the annual variations of arc curvature. While both models can fit the arc curvature variations equally well, the anisotropic model also explains the parabolic arc morphology and its time variation. In this model, the scattering is located at a fractional distance of s = 0.35 ± 0.10, or a distance Ds = 0.19 ± 0.03 kpc from the Earth, likely corresponding to the boundary of the Local Bubble.

We present the interstellar scintillation analysis of fast radio burst (FRB) 20220912A during its extremely active episode in 2022 using data from the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). We detect a scintillation arc in the FRB’s secondary spectrum, which describes the power in terms of the scattered FRB signals’ time delay and Doppler shift. The arc indicates that the scintillation is caused by a highly localized region. Our analysis favors a Milky Way origin of the ionized interstellar medium (IISM) for the localized scattering medium but cannot rule out a host galaxy origin. We present our method for detecting the scintillation arc, which can be applied generally to sources with irregularly spaced bursts or pulses. These methods could help shed light on the complex interstellar environment surrounding the FRBs and in our Galaxy.

Fast radio bursts（FRBs） are highly dispersed millisecond-duration radio bursts, [1,2] of which the physical origin is still not fully understood. FRB 20201124A is one of the most actively repeating FRBs. In this paper, we present the collection of 1863 burst dynamic spectra of FRB 20201124A measured with the Five-hundred-meter Aperture Spherical radio Telescope（FAST）. The current collection, taken from the observation during the FRB active phase from April to June 2021, is the largest burst sample detected for any FRB so far. The standard PSRFITs format is adopted, including dynamic spectra of the burst, and the time information of the dynamic spectra, in addition, mask files help readers to identify the pulse positions are also provided. The dataset is available in Science Data Bank, with the link https://www.doi.org/10.57760/sciencedb.j00113.00076.

毫秒脉冲星是宇宙中稳定的"天然时钟".毫秒脉冲星这一特性可用于建立新的时间保持基准,通过协同原子钟的短期稳定性,形成长期稳定的脉冲星时.利用 40 m 射电望远镜,通过观测若干颗毫秒脉冲星,研究人员开展了脉冲星计时和脉冲星钟方面的研究.目前,已经完成了相关实验平台的搭建、原子钟之间的长期比对和钟差外推等实验,成功地将贝叶斯方法应用于钟差谱估计,初步实现了钟差信号的最优估计和外推.

Observing and timing a group of millisecond pulsars (MSPs) with high rotational stability enables the direct detection of gravitational waves (GWs). The GW signals can be identified from the spatial correlations encoded in the times-of-arrival of widely spaced pulsar-pairs. The Chinese Pulsar Timing Array (CPTA) is a collaboration aiming at the direct GW detection with observations carried out using Chinese radio telescopes. This short article serves as a `table of contents' for a forthcoming series of papers related to the CPTA Data Release 1 (CPTA DR1) which uses observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here, after summarizing the time span and accuracy of CPTA DR1, we report the key results of our statistical inference finding a correlated signal with amplitude $\log A_{\rm c}= -14.4 \,^{+1.0}_{-2.8}$ for spectral index in the range of $\alpha\in [-1.8, 1.5]$ assuming a GW background (GWB) induced quadrupolar correlation. The search for the Hellings-Downs (HD) correlation curve is also presented, where some evidence for the HD correlation has been found that a 4.6-$\sigma$ statistical significance is achieved using the discrete frequency method around the frequency of 14 nHz. We expect that the future International Pulsar Timing Array data analysis and the next CPTA data release will be more sensitive to the nHz GWB, which could verify the current results.

The steerable Jingdong 120-m pulsar radio telescope (JRT) will be built in Jingdong county of Yunnan Province, China. It will become the world's largest fully steerable radio telescope with observation frequencies covering 0.1-10 GHz (3 m- 3 cm). This paper mainly introduces JRT's scientific goals and key technologies. JRT's scientific goals include (1) performing long-term, high-time-density, and high-precision timing observations for more than 90% of millisecond pulsars in the sky to research the construction of a pulsar-based time scale and the detection of nanohertz low-frequency gravitational waves; and (2) contributing observational studies in the fields of pulsar physics, fast radio bursts, gravitational testing, black hole, and VLBI astrometry; (3) serving the national strategic needs in the fields of pulsar navigation, deep space exploration, and space target monitoring. JRT developed key technologies such as large-scale antenna structure design, ultra-wideband feed, low-noise receiver, and multi-functional digital backend. The design and development of each subsystem of JRT will be completed along with relevant domestic research forces. JRT construction will promote China's development in engineering and technical fields, such as large-scale machinery design and processing, automatic control, low-temperature electronics, and system integration. The completion of JRT will progress China's radio astronomy and improve its international influence.