The increasing radio frequency interference(RFI)is a well-recognized problem in radio astronomy research.Pulsars and Fast Radio Bursts(FRBs)are high-priority science targets of the ongoing Commercial Radio Astronomy F...The increasing radio frequency interference(RFI)is a well-recognized problem in radio astronomy research.Pulsars and Fast Radio Bursts(FRBs)are high-priority science targets of the ongoing Commercial Radio Astronomy FAST Survey(CRAFTS).To improve the quality of RFI removal in searches of pulsars and FRBs based on CRAFTS multi-beam data,we here propose an intuitive but powerful RFI mitigation pipeline(CCF-ST).The“CCF-ST”is a spatial filter constructed by signal cross-correlation function(CCF)and Sum-Threshold(ST)algorithm.The RFI marking result is saved in a“mask”file,a binary format for RFI masks in PRESTO.Three known pulsars,PSR B0525-21,PSR B0621-04,and PSR J0943+2252 from CRAFTS L-band 19 beams data are used for evaluation of the performance of CCF-ST in comparison with other methods,such as PRESTO’s“rfifind”,ArPLS-ST and ArPLS-SF.The result shows that CCF-ST can reduce effective data loss rate and improves the detected signal-to-noise ratio of the pulsations by~26%and~18%respectively compared with PRESTO’s“rfifind”and ArPLS-ST.The CCF-ST also has the advantage of low computational cost,e.g.,reducing the time consumption by~40%and memory consumption by~90%compared with ArPLS-SF.We expect that the new RFI mitigation and analysis toolkit(CCF-ST)demonstrated in this paper can be applied to CRAFTS and other multi-beam telescope observations to improve the data quality and efficiency of pulsar and FRB searches.展开更多
We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB20201124A with the Five-hundred-meter Aperture Spherical radio Telescope(FAST)during an extremely active epis...We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB20201124A with the Five-hundred-meter Aperture Spherical radio Telescope(FAST)during an extremely active episode on UTC 2021 September 25–28 in a series of four papers.In this second paper of the series,we study the energy distribution of 881 bursts(defined as significant signals separated by dips down to the noise level)detected in the first four days of our 19 hr observational campaign spanning 17 days.The event rate initially increased exponentially but the source activity stopped within 24 hr after the 4th day.The detection of 542 bursts in one hour during the fourth day marked the highest event rate detected from one single FRB source so far.The bursts have complex structures in the time-frequency space.We find a double-peak distribution of the waiting time,which can be modeled with two log-normal functions peaking at 51.22 ms and 10.05 s,respectively.Compared with the emission from a previous active episode of the source detected with FAST,the second distribution peak time is smaller,suggesting that this peak is defined by the activity level of the source.We calculate the isotropic energy of the bursts using both a partial bandwidth and a full bandwidth and find that the energy distribution is not significantly changed.We find that an exponentially connected broken-power law function can fit the cumulative burst energy distribution well,with the lower and higher-energy indices being-1.22±0.01 and-4.27±0.23,respectively.Assuming a radio radiative efficiency ofη_(r)=10^(-4),the total isotropic energy of the bursts released during the four days when the source was active is already 3.9×10^(46)erg,exceeding~23%of the available magnetar dipolar magnetic energy.This challenges the magnetar models which invoke an inefficient radio emission(e.g.,synchrotron maser models).展开更多
We report the properties of more than 600 bursts(including cluster-bursts)detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an ...We report the properties of more than 600 bursts(including cluster-bursts)detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25–28,in a series of four papers.The observations were carried out in the band of 1.0–1.5 GHz by using the center beam of the L-band 19-beam receiver.We monitored the source in sixteen1 hr sessions and one 3 hr session spanning 23 days.All the bursts were detected during the first four days.In this first paper of the series,we perform a detailed morphological study of 624 bursts using the two-dimensional frequencytime“waterfall”plots,with a burst(or cluster-burst)defined as an emission episode during which the adjacent emission peaks have a separation shorter than 400 ms.The duration of a burst is therefore always longer than 1 ms,with the longest up to more than 120 ms.The emission spectra of the sub-bursts are typically narrow within the observing band with a characteristic width of~277 MHz.The center frequency distribution has a dominant peak at about 1091.9 MHz and a secondary weak peak around 1327.9 MHz.Most bursts show a frequencydownwarddrifting pattern.Based on the drifting patterns,we classify the bursts into five main categories:downward drifting(263)bursts,upward drifting(3)bursts,complex(203),no drifting(35)bursts,and no evidence for drifting(121)bursts.Subtypes are introduced based on the emission frequency range in the band(low,middle,high and wide)as well as the number of components in one burst(1,2,or multiple).We measured a varying scintillation bandwidth from about 0.5 MHz at 1.0 GHz to 1.4 MHz at 1.5 GHz with a spectral index of 3.0.展开更多
We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode ...We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25th-28th in a series of four papers.In this fourth paper of the series,we present a systematic search of the spin period and linear acceleration of the source object from both 996 individual pulse peaks and the dedispersed time series.No credible spin period was found from this data set.We rule out the presence of significant periodicity in the range between 1 ms and 100 s with a pulse duty cycle<0.49±0.08(when the profile is defined by a von-Mises function,not a boxcar function)and linear acceleration up to 300 m s^(-2)in each of the four one-hour observing sessions,and up to 0.6 m s^(-2)in all 4 days.These searches contest theoretical scenarios involving a 1 ms–100 s isolated magnetar/pulsar with surface magnetic field<10^(15)G and a small duty cycle(such as in a polar-cap emission mode)or a pulsar with a companion star or black hole up to 100 M_(⊙)and P_(b)>10 hr.We also perform a periodicity search of the fine structures and identify 53 unrelated millisecond-timescale“periods”in multicomponents with the highest significance of 3.9σ.The“periods”recovered from the fine structures are neither consistent nor harmonically related.Thus they are not likely to come from a spin period.We caution against claiming spin periodicity with significance below~4σwith multi-components from one-off FRBs.We discuss the implications of our results and the possible connections between FRB multi-components and pulsar microstructures.展开更多
As the most widely consumed beverage in the world,tea has various nutritional,economic,and global cultural values.With the development of the third-generation sequencing technology,several genome sequences of tea plan...As the most widely consumed beverage in the world,tea has various nutritional,economic,and global cultural values.With the development of the third-generation sequencing technology,several genome sequences of tea plants have been published.These genomic data have pivotal information that is of benefit to tea plant breeders and biologists in advancing tea plant improvement and the final quality of tea products.We hereby present the integrative online database,Tea Plant Genome Database(TeaPGDB;http://eplant.njau.edu.cn/tea),which incorporates the published genome sequences of tea plants.The current release of TeaPGDB hosts published tea plant genome data with various online tools,including JBrowse,gene search,SSR search,BLAST.TeaPGDB also contains a download server,which provides access for the download of genome-related data and rich annotation files.TeaPGDB is committed to collecting,integrating,and annotating published tea plant genome data,providing data support for research on tea plant heredity,evolution,breeding for resistance,plant improvement,and facilitating the characterization of important traits or flavor related genes in the community.Compared with other tea plant databases,this database not only contains more complete genome data and gene annotation information,but also has a user-friendly interface for researchers in the field.展开更多
We report the radio observations of the eclipsing black widow pulsar J1720-0534, a 3.26 ms pulsar in orbit with a low mass companion of mass 0.029 to 0.034 M⊙. We obtain the phase-connected timing ephemeris and polar...We report the radio observations of the eclipsing black widow pulsar J1720-0534, a 3.26 ms pulsar in orbit with a low mass companion of mass 0.029 to 0.034 M⊙. We obtain the phase-connected timing ephemeris and polarization profile of this millisecond pulsar(MSP) using the Five-hundred-meter Aperture Spherical radio Telescope(FAST), the Green Bank Telescope(GBT), and the Parkes Telescope. For the first time from such a system, an oscillatory polarization angle change was observed from a particular eclipse egress with partial depolarization, indicating 10-milliGauss-level reciprocating magnetic fields oscillating in a length scale of 5 ×10^(3)km(assuming an orbital inclination angle of 90°) outside the companion's magnetosphere. The dispersion measure variation observed during the ingresses and egresses shows the rapid raising of the electron density in the shock boundary between the companion's magnetosphere and the surrounding pulsar wind. We suggest that the observed oscillatory magnetic fields originate from the pulsar wind outside the companion's magnetosphere.展开更多
Environments play an important role in galaxy formation and evolution,particularly in regulating the content of neutral gas.However,current HI surveys have limitations in their depth,which prevents them from adequatel...Environments play an important role in galaxy formation and evolution,particularly in regulating the content of neutral gas.However,current HI surveys have limitations in their depth,which prevents them from adequately studying low HI content galaxies in high-density regions.In this study,we address this issue by employing the Five-hundred-meter Aperture Spherical radio Telescope with extensive integration times to complement the relatively shallow Arecibo Legacy Fast Arecibo L-band Feed Array HI survey.This approach allows us to explore the gas content of dwarf galaxies across various environments.We observe a positive relationship between HI mass and stellar mass in dwarf galaxies,with a well-defined upper boundary for HI mass that holds true in both observations and simulations.Furthermore,we find a decrease in the H I-to-stellar mass ratio(M_(HI)/M_*)as the density of the environment increases,irrespective of whether it is determined by the proximity to the nearest group or the projected number density.Comparing our observations to simulations,we note a steeper slope in the relationship,indicating a gradual gas-stripping process in the observational data.Additionally,we find that the scaling relation between the M_(HI)/M_*and optical properties can be improved by incorporating galaxy environments.展开更多
Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s positio...Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s position is arcminutes off from its true position.Such a position error leads to significant arrival time shifts as a result of the Earth’s orbital motion.Traditional down-hill fitting timing algorithms become ineffective when our model predicts the wrong pulse rotations for our next observation.For some pulsars whose model prediction is not too far off,the correct rotation number could be found by trial-and-error methods.For the remaining challenging pulsars,a more generalized method is called for.This paper proposes a GPU-based algorithm that could exhaustively search a large area of trail positions for probable timing solutions.This could help find phase-connected timing solutions for new pulsars using brute force.展开更多
Rotating Radio Transients(RRATs)are a relatively new subclass of pulsars that emit detectable radio bursts sporadically.We analyzed 10 RRATs observed using the Parkes telescope,with eight of these observed via the ult...Rotating Radio Transients(RRATs)are a relatively new subclass of pulsars that emit detectable radio bursts sporadically.We analyzed 10 RRATs observed using the Parkes telescope,with eight of these observed via the ultra-wide-bandwidth low-frequency(UWL)receiver.We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs.We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs.All of their integrated pulses follow a simple power law,consistent with the known range of pulsar spectral indices.Their average spectral indices of single pulses are-0.9,-1.2,and-1.0 respectively,which are within the known range of pulsar spectral indices.Additionally,we find that the spreads of single-pulse spectral indices for these RRATs(ranging from-3.5 to+0.5)are narrower compared to what has been observed in other RRATs.Notably,the average spectral index and scatter of single pulses are both relatively small.For the remaining five RRATs observed at the UWL receiver,we also provide the upper limits on fluence and flux density.In addition,we obtain the timing solution of PSR J1709-43.Our analysis shows that PSRs J1919+1745,J1709-43,and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.展开更多
Using micromagnetic simulations, we demonstrate the tilted perpendicular anisotropy-induced spin-orbit ratchet effect. In spin-orbit torque(SOT)-induced magnetization switching, the critical currents required to switc...Using micromagnetic simulations, we demonstrate the tilted perpendicular anisotropy-induced spin-orbit ratchet effect. In spin-orbit torque(SOT)-induced magnetization switching, the critical currents required to switch between the two magnetization states(upward and downward magnetization) are asymmetric. In addition, in the nanowire structure, tilted anisotropy induces formation of tilted domain walls(DWs). The tilted DWs exhibit a ratchet behavior during motion. The ratchet effect during switching and DW motions can be tuned by changing the current direction with respect to the tilting direction of anisotropy. The ratchet motion of the DWs can be used to mimic the leaky-integrate-fire function of a biological neuron, especially the asymmetric property of the “potential” and “reset” processes. Our results provide a full understanding of the influence of tilted perpendicular anisotropy on SOT-induced magnetization switching and DW motion, and are beneficial for designs of further SOT-based devices.展开更多
We report the discovery of PSR J1909+0122 by the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)as part of the Commensal Radio Astronomy FAST Survey.PSR J1909+0122 has a spin period of 1.257 s and a disper...We report the discovery of PSR J1909+0122 by the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)as part of the Commensal Radio Astronomy FAST Survey.PSR J1909+0122 has a spin period of 1.257 s and a dispersion measure of 186.2 pc cm^(-3).The averaged pulse profile shows two distinct components.We performed a single-pulse study based on a one-hour observation at 1.25 GHz on 2021 August 23.We used a threshold of 5σ_(ep) to measure the nulling fraction(NF)as 63%±1.5%.The longitude-resolved fluctuation spectra and fast Fourier transform spectra of the binary sequences revealed the quasi-periodicity of nulling with a period of 30 rotation periods.We examined the reliability of the periodicity by comparing it to random noise injection.The NF,E,and modulation periodicity P_(M) of PSR J1909+0122 were compared with other periodic nulling pulsars,showing that the source of J1909+0122 has the second largest NF in the population.Long-term timing observations over six months were used to derive the phase-connected ephemeris of this pulsar.The measured P and P values disfavor dipolar geometry for polar gap models,and the prediction for a space-charge-limited flow model in the case of inverse Compton scattering is only just above the death line.In this work,PSR J1909+0122 has revealed possible correlations between nulling behavior and pulsar properties,which will help to shed light on the pulsar emission mechanism and its temporal evolution in future observations.展开更多
We report the results of a search for radio pulsars in five supernova remnants(SNRs)with the FAST telescope.The observations were made using the 19-beam receiver in“snapshot”mode.The integration time for each pointi...We report the results of a search for radio pulsars in five supernova remnants(SNRs)with the FAST telescope.The observations were made using the 19-beam receiver in“snapshot”mode.The integration time for each pointing was 10 min.We discovered a new pulsar,PSR J1845–0306,which has a spin period of 983.6 ms and a dispersion measure of 444.6±2.0 cm^(−3)·pc,in observations of SNR G29.6+0.1.To judge the association between the pulsar and the SNR,further verification is needed.We also re-detected some known pulsars in the data from SNRs G29.6+0.1 and G29.7–0.3.No pulsars were detected in the observations of the other three SNRs.展开更多
The most extensive survey of carbon monoxide(CO)gas in the Taurus molecular cloud relied on ^(12)CO and ^(13)CO J=1→0 emission only,distinguishing the region where ^(12)CO is detected without ^(13)CO(named mask 1 reg...The most extensive survey of carbon monoxide(CO)gas in the Taurus molecular cloud relied on ^(12)CO and ^(13)CO J=1→0 emission only,distinguishing the region where ^(12)CO is detected without ^(13)CO(named mask 1 region)from the one where both are detected(mask 2 region)(Goldsmith et al.2008;Pineda et al.2010).We have taken advantage of recent ^(12)CO J=3→2 James Clerk Maxwell Telescope observations,where they include mask 1regions to estimate density,temperature,and N(CO)with a large velocity gradient model.This represents 1395 pixels out of~1.2 million in the mark 1 region.Compared to Pineda et al.(2010)results and assuming a Tkin of 30 K,we find a higher volume density of molecular hydrogen of 3.3×10^(3) cm^(-3),compared to their 250-700 cm^(-3),and a CO column density of 5.7×10^(15)cm^(-2),about a quarter of their value.The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium.Future observations to extend the ^(12)CO J=3→2 mapping further away from the ^(13)COdetected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.展开更多
Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood.The protoplanetary disks are the birthplace of planets and its distinctive environment provides an intriguing platform ...Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood.The protoplanetary disks are the birthplace of planets and its distinctive environment provides an intriguing platform for investigating models of sulfur chemistry.We analyzed the Atacama Large Millimeter/submillimeter Array observations of CS 7-6 transitions in the HD 163296 disk and performed astrochemical modeling to explore its sulfur chemistry.We simulated the distribution of sulfur-containing molecules and compared it with observationally deduced fractional column densities.We have found that the simulated column density of CS is consistent with the observationally deduced fractional column densities,while the simulated column density of C_(2)S is lower than the observationally deduced upper limits on column densities.This results indicate that we have a good understanding of the chemical properties of CS and C_(2)S in the disk.We also investigated the influence of the C/O ratio on sulfur-containing molecules and found that the column densities of SO,SO_(2),and H_2S near the centra star are dependent on the C/O ratio.Additionally,we found that the N[CS]/N[SO]ratio can serve as a promising indicator of the disk’s C/O ratio in HD 163296.Overall,the disk of HD 163296 provides a favorable environmen for the detection of sulfur-containing molecules.展开更多
As the third paper in the multiple-part series,we report the statistical properties of radio bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical ...As the third paper in the multiple-part series,we report the statistical properties of radio bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode between the 25th and 28th of September 2021(UT).We focus on the polarization properties of536 bright bursts with S/N>50.We found that the Faraday rotation measures(RMs)monotonically dropped from-579to-605 rad m^(-2)in the 4 day window.The RM values were compatible with the values(-300 to-900 rad m^(-2))reported 4 months ago.However,the RM evolution rate in the current observation window was at least an order of magnitude smaller than the one(~500 rad m^(-2)day^(-1))previously reported during the rapid RM-variation phase,but is still higher than the one(≤1 rad m^(-2)day^(-1))during the later RM no-evolution phase.The bursts of FRB 20201124A were highly polarized with the total degree of polarization(circular plus linear)greater than 90%for more than 90%of all bursts.The distribution of linear polarization position angles(PAs),degree of linear polarization(L/I)and degree of circular polarization(V/I)can be characterized with unimodal distribution functions.During the observation window,the distributions became wider with time,i.e.,with larger scatter,but the centroids of the distribution functions remained nearly constant.For individual bursts,significant PA variations(confidence level 5σ)were observed in 33%of all bursts.The polarization of single pulses seems to follow certain complex trajectories on the Poincarésphere,which may shed light on the radiation mechanism at the source or the plasma properties along the path of FRB propagation.展开更多
This paper presents data from a 21 cm H I emission drift scan observation of a field partially covering the NGC 4636 galaxy group with the Five-hundred meter Aperture Radio Telescope(FAST). We construct a pipeline to ...This paper presents data from a 21 cm H I emission drift scan observation of a field partially covering the NGC 4636 galaxy group with the Five-hundred meter Aperture Radio Telescope(FAST). We construct a pipeline to reduce the data, and use So Fi A for source finding. When not contaminated by Radio Frequency Interference(RFI), the FAST observations are capable of detecting all of the galaxies previously detected by the Arecibo Legacy Fast ALFA(ALFALFA) survey in the same region. Comparing to ALFALFA for the detections in common, the FAST data show consistent integrated spectra when the H I disks are spatially unresolved, and capture more flux when the H I disks are resolved. The FAST data further reveal 10 new detections in the region mutually covered with ALFALFA, and 18 new detections beyond the footprint of ALFALFA. All of the new detections have the matching optical counterparts. For the member galaxies of the NGC 4636 group, the detection limit of FAST is deeper by 0.4 dex in H I mass than that of the ALFALFA data. After correcting for the incompleteness caused by RFI contamination, we show that the H I detection rate of galaxies rises steeply with radius out to the virial radius of the group, and flattens beyond that. We also examine four spatially resolved galaxy systems with potential tidal interaction features in detail. Considering that the data have been taken during the“shared-risk” period before a major source of local RFI was eliminated, the results highlight the power of FAST in detecting extragalactic H I.展开更多
The growing scale and complexity of component interactions in cloud computing systems post great challenges for operators to understand the characteristics of system performance. Profiling has long been proved to be a...The growing scale and complexity of component interactions in cloud computing systems post great challenges for operators to understand the characteristics of system performance. Profiling has long been proved to be an effective approach to performance analysis; however, existing approaches confront new challenges that emerge in cloud computing systems. First, the efficiency of the profiling becomes of critical concern; second, service-oriented profiling should be considered to support separation-of-concerns performance analysis. To address the above issues, in this paper, we present P-Tracer, an online performance profiling tool specifically tailored for cloud computing systems. P-Tracer constructs a specific search engine that proactively processes performance logs and generates a particular index for fast queries; second, for each service, P-Tracer retrieves a statistical insight of performance characteristics from multi-dimensions and provides operators with a suite of web-based interfaces to query the critical information. We evaluate P- Tracer in the aspects of tracing overheads, data preprocessing scalability and querying efficiency. Three real-world case studies that happened in Alibaba cloud computing platform demonstrate that P-Tracer can help operators understand soft-ware behaviors and localize the primary causes of performance anomalies effectively and efficiently.展开更多
Magnetic fields are pervasive throughout the Universe.They are integral to a wide array of astrophysical processes that span various physical scales and field strengths.The Galactic magnetic field,in particular,holds ...Magnetic fields are pervasive throughout the Universe.They are integral to a wide array of astrophysical processes that span various physical scales and field strengths.The Galactic magnetic field,in particular,holds significant importance in shaping the evolution of our Galaxy.However,our understanding of its behavior on small scales remains poor,especially when considering its penetration into the Galactic halo[1].展开更多
We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We...We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We simulate 105and 106localized FRBs from a 10-year SKA observation,and find that:(1)using 106FRB data alone can tightly constrain dark-energy equation of state parameters better than CMB+BAO+SNe,providing an independent cosmological probe to explore dark energy;(2)combining the FRB data with gravitational-wave standard siren data from 10-year observation with the Einstein Telescope,the Hubble constant can be constrained to a sub-percent level,serving as a powerful low-redshift probe;(3)using 106FRB data can constrain the baryon density?bh to a precision of~0.1%.Our results indicate that SKA-era FRBs will provide precise cosmological measurements to shed light on both dark energy and the missing baryon problem,and help resolve the Hubble tension.展开更多
Fast radio bursts(FRBs)are bright millisecond-duration radio transients first discovered by Lorimer et al.[1].While their cosmological origin and energetic naturemake them ideal tools for probing a range of astrophysi...Fast radio bursts(FRBs)are bright millisecond-duration radio transients first discovered by Lorimer et al.[1].While their cosmological origin and energetic naturemake them ideal tools for probing a range of astrophysics[2],their progenitors and radiation mechanisms are still unknown.Aparticularlyinteresting subset of FRBs is the so-called repeating FRBs,which recurrently emit millisecond-duration radio bursts.展开更多
基金supported by National Natural Science Foundation of China(NSFC)under Nos.11988101,U183110134,11703047,11773041,and U1831131support by the Youth Innovation Promotion Association CAS(id.2021055)cultivation project for FAST scientific payoff and research achievement of CAMS-CAS。
文摘The increasing radio frequency interference(RFI)is a well-recognized problem in radio astronomy research.Pulsars and Fast Radio Bursts(FRBs)are high-priority science targets of the ongoing Commercial Radio Astronomy FAST Survey(CRAFTS).To improve the quality of RFI removal in searches of pulsars and FRBs based on CRAFTS multi-beam data,we here propose an intuitive but powerful RFI mitigation pipeline(CCF-ST).The“CCF-ST”is a spatial filter constructed by signal cross-correlation function(CCF)and Sum-Threshold(ST)algorithm.The RFI marking result is saved in a“mask”file,a binary format for RFI masks in PRESTO.Three known pulsars,PSR B0525-21,PSR B0621-04,and PSR J0943+2252 from CRAFTS L-band 19 beams data are used for evaluation of the performance of CCF-ST in comparison with other methods,such as PRESTO’s“rfifind”,ArPLS-ST and ArPLS-SF.The result shows that CCF-ST can reduce effective data loss rate and improves the detected signal-to-noise ratio of the pulsations by~26%and~18%respectively compared with PRESTO’s“rfifind”and ArPLS-ST.The CCF-ST also has the advantage of low computational cost,e.g.,reducing the time consumption by~40%and memory consumption by~90%compared with ArPLS-SF.We expect that the new RFI mitigation and analysis toolkit(CCF-ST)demonstrated in this paper can be applied to CRAFTS and other multi-beam telescope observations to improve the data quality and efficiency of pulsar and FRB searches.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11988101 and 11725313)supported by the Open Project Program of the Key Laboratory of FAST,Chinese Academy of Sciences+11 种基金support from the National Natural Science Foundation of China(NSFC,Grant No.U2031117)the Youth Innovation Promotion Association CAS(id.2021055)CAS Project for Young Scientists in Basic Research(grant YSBR-006)the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the Key Research Project of Zhejiang Lab No.2021PE0AC0supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11988101 and 11833009)the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWSLH021)supported by the Cultivation Project for the FAST scientific Payoff and Research Achievement of CAMSCASsupported by National SKA Program of China 2020SKA0120200National Natural Science Foundation of China(NSFC,Grant No.12041303)the CAS-MPG LEGACY projectfunding from the MaxPlanck Partner Group。
文摘We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB20201124A with the Five-hundred-meter Aperture Spherical radio Telescope(FAST)during an extremely active episode on UTC 2021 September 25–28 in a series of four papers.In this second paper of the series,we study the energy distribution of 881 bursts(defined as significant signals separated by dips down to the noise level)detected in the first four days of our 19 hr observational campaign spanning 17 days.The event rate initially increased exponentially but the source activity stopped within 24 hr after the 4th day.The detection of 542 bursts in one hour during the fourth day marked the highest event rate detected from one single FRB source so far.The bursts have complex structures in the time-frequency space.We find a double-peak distribution of the waiting time,which can be modeled with two log-normal functions peaking at 51.22 ms and 10.05 s,respectively.Compared with the emission from a previous active episode of the source detected with FAST,the second distribution peak time is smaller,suggesting that this peak is defined by the activity level of the source.We calculate the isotropic energy of the bursts using both a partial bandwidth and a full bandwidth and find that the energy distribution is not significantly changed.We find that an exponentially connected broken-power law function can fit the cumulative burst energy distribution well,with the lower and higher-energy indices being-1.22±0.01 and-4.27±0.23,respectively.Assuming a radio radiative efficiency ofη_(r)=10^(-4),the total isotropic energy of the bursts released during the four days when the source was active is already 3.9×10^(46)erg,exceeding~23%of the available magnetar dipolar magnetic energy.This challenges the magnetar models which invoke an inefficient radio emission(e.g.,synchrotron maser models).
基金supported by the National Natural Science Foundation of China(NSFC,Nos.11988101 and 11833009)the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWSLH021)+6 种基金supported by the Cultivation Project for the FAST scientific Payoff and Research Achievement of CAMS-CASsupported by the Key Research Project of Zhejiang Lab no.2021PE0AC0supported by the National SKA Program of China(2020SKA0120100)the National Key R&D Program of China(2017YFA0402602)the National Natural Science Foundation of China(No.12041303)the CAS-MPG LEGACY projectfunding from the MaxPlanck Partner Group。
文摘We report the properties of more than 600 bursts(including cluster-bursts)detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25–28,in a series of four papers.The observations were carried out in the band of 1.0–1.5 GHz by using the center beam of the L-band 19-beam receiver.We monitored the source in sixteen1 hr sessions and one 3 hr session spanning 23 days.All the bursts were detected during the first four days.In this first paper of the series,we perform a detailed morphological study of 624 bursts using the two-dimensional frequencytime“waterfall”plots,with a burst(or cluster-burst)defined as an emission episode during which the adjacent emission peaks have a separation shorter than 400 ms.The duration of a burst is therefore always longer than 1 ms,with the longest up to more than 120 ms.The emission spectra of the sub-bursts are typically narrow within the observing band with a characteristic width of~277 MHz.The center frequency distribution has a dominant peak at about 1091.9 MHz and a secondary weak peak around 1327.9 MHz.Most bursts show a frequencydownwarddrifting pattern.Based on the drifting patterns,we classify the bursts into five main categories:downward drifting(263)bursts,upward drifting(3)bursts,complex(203),no drifting(35)bursts,and no evidence for drifting(121)bursts.Subtypes are introduced based on the emission frequency range in the band(low,middle,high and wide)as well as the number of components in one burst(1,2,or multiple).We measured a varying scintillation bandwidth from about 0.5 MHz at 1.0 GHz to 1.4 MHz at 1.5 GHz with a spectral index of 3.0.
基金supported by the National SKA Program of China(Nos.2020SKA0120200 and 2020SKA0120100)the National Natural Science Foundation of China(Grant Nos.12041303,11873067 and 12041304)+4 种基金the National Key R&D Program of China(Nos.2017YFA0402600,2021YFA0718500 and 2017YFA0402602)the CAS-MPG LEGACY project,the Max-Planck Partner Group,the Key Research Project of Zhejiang Lab(No.2021PE0AC0)supported by the National Natural Science Foundation of China(NSFC,Nos.11988101 and 11833009)the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWSLH021)supported by the Cultivation Project for the FAST scientific Payoff and Research Achievement of CAMS-CAS。
文摘We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25th-28th in a series of four papers.In this fourth paper of the series,we present a systematic search of the spin period and linear acceleration of the source object from both 996 individual pulse peaks and the dedispersed time series.No credible spin period was found from this data set.We rule out the presence of significant periodicity in the range between 1 ms and 100 s with a pulse duty cycle<0.49±0.08(when the profile is defined by a von-Mises function,not a boxcar function)and linear acceleration up to 300 m s^(-2)in each of the four one-hour observing sessions,and up to 0.6 m s^(-2)in all 4 days.These searches contest theoretical scenarios involving a 1 ms–100 s isolated magnetar/pulsar with surface magnetic field<10^(15)G and a small duty cycle(such as in a polar-cap emission mode)or a pulsar with a companion star or black hole up to 100 M_(⊙)and P_(b)>10 hr.We also perform a periodicity search of the fine structures and identify 53 unrelated millisecond-timescale“periods”in multicomponents with the highest significance of 3.9σ.The“periods”recovered from the fine structures are neither consistent nor harmonically related.Thus they are not likely to come from a spin period.We caution against claiming spin periodicity with significance below~4σwith multi-components from one-off FRBs.We discuss the implications of our results and the possible connections between FRB multi-components and pulsar microstructures.
基金the National Key R&D Program of China(2020YFE0202900)The National Natural Science Foundation of China(31972460,31870680)+5 种基金the earmarked fund for China Agriculture Research System(CARS-19)the Key Research and Development Program of Jiangsu Province(BE2019379)Jiangsu Agriculture Science and Technology Innovation Fund(CX(20)2004)Innovation and Extension Projects of Forestry Science and Technology in Jiangsu Province(LYKJ-Changzhou[2020]03)Changzhou Science and Technology Support Program(Agriculture CE20202003)Chuzhou Science and Technology Support Program(2020ZN009).
文摘As the most widely consumed beverage in the world,tea has various nutritional,economic,and global cultural values.With the development of the third-generation sequencing technology,several genome sequences of tea plants have been published.These genomic data have pivotal information that is of benefit to tea plant breeders and biologists in advancing tea plant improvement and the final quality of tea products.We hereby present the integrative online database,Tea Plant Genome Database(TeaPGDB;http://eplant.njau.edu.cn/tea),which incorporates the published genome sequences of tea plants.The current release of TeaPGDB hosts published tea plant genome data with various online tools,including JBrowse,gene search,SSR search,BLAST.TeaPGDB also contains a download server,which provides access for the download of genome-related data and rich annotation files.TeaPGDB is committed to collecting,integrating,and annotating published tea plant genome data,providing data support for research on tea plant heredity,evolution,breeding for resistance,plant improvement,and facilitating the characterization of important traits or flavor related genes in the community.Compared with other tea plant databases,this database not only contains more complete genome data and gene annotation information,but also has a user-friendly interface for researchers in the field.
基金The Parkes Radio Telescope (Murriyang) is part of the Australia Telescope National Facility, which is funded by the Australian Government for operation as a National Facility managed by CSIROsupported by the National Natural Science Foundation of China (NSFC) grant Nos. 12041303, 12041304, 11873067, 12133004, 12203045, 12203070, 12203072, 12103013, U2031117 and T2241020+11 种基金the CAS-MPG LEGACY project and the National SKA Program of China No. 2020SKA0120200the Foundation of Science and Technology of Guizhou Province No. ((2021)023)the Foundation of Guizhou Provincial Education Department (No.KY(2021)303)the National Key Research and Development Program of China Nos. 2022YFC2205202 and 2022YFC2205203the Major Science and Technology Program of Xinjiang Uygur Autonomous Region Nos. 2022A03013-1, 2022A03013-3 and 2022A03013-4the National Key Research and Development Program of China No. 2022YFC2205203the 2021 project Xinjiang Uygur autonomous region of China for Tianshan elites and the Youth Innovation Promotion Association of CAS under No. 2023069support from the Youth Innovation Promotion Association CAS (id. 2021055)CAS Project for Young Scientists in Basic Research (grant YSBR-006)the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupport from Zhejiang Provincial Natural Science Foundation of China under grant No. LY23A030001supported by the NSF Physics Frontiers Center award number 2020265。
文摘We report the radio observations of the eclipsing black widow pulsar J1720-0534, a 3.26 ms pulsar in orbit with a low mass companion of mass 0.029 to 0.034 M⊙. We obtain the phase-connected timing ephemeris and polarization profile of this millisecond pulsar(MSP) using the Five-hundred-meter Aperture Spherical radio Telescope(FAST), the Green Bank Telescope(GBT), and the Parkes Telescope. For the first time from such a system, an oscillatory polarization angle change was observed from a particular eclipse egress with partial depolarization, indicating 10-milliGauss-level reciprocating magnetic fields oscillating in a length scale of 5 ×10^(3)km(assuming an orbital inclination angle of 90°) outside the companion's magnetosphere. The dispersion measure variation observed during the ingresses and egresses shows the rapid raising of the electron density in the shock boundary between the companion's magnetosphere and the surrounding pulsar wind. We suggest that the observed oscillatory magnetic fields originate from the pulsar wind outside the companion's magnetosphere.
基金supported by the National SKA Program of China(Nos.2022SKA0110201 and 2022SKA0110200)CAS Project for Young Scientists in Basic Research grant No.YSBR-062+11 种基金the National Natural Science Foundation of China(NSFC)(grant Nos.12033008,11622325,11988101)the K.C.Wong Education Foundationthe science research grants from the China Manned Space Project(CMSP)with NO.CMS-CSST-2021-A03 and NO.CMS-CSST-2021-A07support of the Tsinghua Shui Mu ScholarshipNSFC(grant No.12073014)the science research grants from the China Manned Space Project with No.CMS-CSST2021-A05Tsinghua University Initiative Scientific Research Program(No.20223080023)supported by NSFC(grant Nos.11988101,12041302,and U1931110)supported by the science research grant from the China Manned Space Project with grant No.CMS-CSST-2021-A08support from the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sk?odowska-Curie grant agreement No.101086388supported by the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the Key Research Project of Zhejiang Lab(No.2021PE0AC03)。
文摘Environments play an important role in galaxy formation and evolution,particularly in regulating the content of neutral gas.However,current HI surveys have limitations in their depth,which prevents them from adequately studying low HI content galaxies in high-density regions.In this study,we address this issue by employing the Five-hundred-meter Aperture Spherical radio Telescope with extensive integration times to complement the relatively shallow Arecibo Legacy Fast Arecibo L-band Feed Array HI survey.This approach allows us to explore the gas content of dwarf galaxies across various environments.We observe a positive relationship between HI mass and stellar mass in dwarf galaxies,with a well-defined upper boundary for HI mass that holds true in both observations and simulations.Furthermore,we find a decrease in the H I-to-stellar mass ratio(M_(HI)/M_*)as the density of the environment increases,irrespective of whether it is determined by the proximity to the nearest group or the projected number density.Comparing our observations to simulations,we note a steeper slope in the relationship,indicating a gradual gas-stripping process in the observational data.Additionally,we find that the scaling relation between the M_(HI)/M_*and optical properties can be improved by incorporating galaxy environments.
基金supported by the National Natural Science Foundation of China(12041303)the National SKA Program of China(2020SKA0120200)+2 种基金the CAS Project for Young Scientists in Basic Research YSBR-063the National Natural Science Foundation of China(NSFC grant Nos.12203070 and Nos.12203072)the CAS-MPG LEGACY project。
文摘Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s position is arcminutes off from its true position.Such a position error leads to significant arrival time shifts as a result of the Earth’s orbital motion.Traditional down-hill fitting timing algorithms become ineffective when our model predicts the wrong pulse rotations for our next observation.For some pulsars whose model prediction is not too far off,the correct rotation number could be found by trial-and-error methods.For the remaining challenging pulsars,a more generalized method is called for.This paper proposes a GPU-based algorithm that could exhaustively search a large area of trail positions for probable timing solutions.This could help find phase-connected timing solutions for new pulsars using brute force.
基金supported by the Major Science and Technology Program of Xinjiang Uygur Autonomous Region(grant no.2022A03013-4)the Zhejiang Provincial Natural Science Foundation of China(grant no.LY23A030001)+4 种基金the National SKA Program of China(grant no.2020SKA0120100,2022YFC2205201,2020SKA0120200)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(grant no.2022D01D85)the National Natural Science Foundation of China(NSFC,grant Nos.12041304,12273100,and 12041303)the West Light Foundation of Chinese Academy of Sciences(grant no.WLFC 2021-XBQNXZ-027)the open program of the Key Laboratory of Xinjiang Uygur Autonomous Region(grant no.2020D04049)。
文摘Rotating Radio Transients(RRATs)are a relatively new subclass of pulsars that emit detectable radio bursts sporadically.We analyzed 10 RRATs observed using the Parkes telescope,with eight of these observed via the ultra-wide-bandwidth low-frequency(UWL)receiver.We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs.We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs.All of their integrated pulses follow a simple power law,consistent with the known range of pulsar spectral indices.Their average spectral indices of single pulses are-0.9,-1.2,and-1.0 respectively,which are within the known range of pulsar spectral indices.Additionally,we find that the spreads of single-pulse spectral indices for these RRATs(ranging from-3.5 to+0.5)are narrower compared to what has been observed in other RRATs.Notably,the average spectral index and scatter of single pulses are both relatively small.For the remaining five RRATs observed at the UWL receiver,we also provide the upper limits on fluence and flux density.In addition,we obtain the timing solution of PSR J1709-43.Our analysis shows that PSRs J1919+1745,J1709-43,and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.
基金supported by the National Natural Science Foundation of China (Grant No.12274108)the Natural Science Foundation of Zhejiang Province (Grant Nos.LY23A040008 and LY23A040008)the Basic Scientific Research Project of Wenzhou (Grant No.G20220025)。
文摘Using micromagnetic simulations, we demonstrate the tilted perpendicular anisotropy-induced spin-orbit ratchet effect. In spin-orbit torque(SOT)-induced magnetization switching, the critical currents required to switch between the two magnetization states(upward and downward magnetization) are asymmetric. In addition, in the nanowire structure, tilted anisotropy induces formation of tilted domain walls(DWs). The tilted DWs exhibit a ratchet behavior during motion. The ratchet effect during switching and DW motions can be tuned by changing the current direction with respect to the tilting direction of anisotropy. The ratchet motion of the DWs can be used to mimic the leaky-integrate-fire function of a biological neuron, especially the asymmetric property of the “potential” and “reset” processes. Our results provide a full understanding of the influence of tilted perpendicular anisotropy on SOT-induced magnetization switching and DW motion, and are beneficial for designs of further SOT-based devices.
基金supported by the National Natural Science Foundation of China(NSFC)Grant Nos.11988101,1172531312041303,12041304,12203045,12203070,12103013,T2241020the National SKA Program of China(Nos.2020SKA0120200,2022SKA0130100,2022SKA0130104)+5 种基金the Foundation of Science and Technology of Guizhou Province(No.(2021)023)the Foundation of Guizhou Provincial Education Department(Nos.KY(2021)303,KY(2020)003)support from the National Natural Science Foundation of China under grant U2031117the Youth Innovation Promotion Association CAS(id.2021055)CAS Project for Young Scientists in Basic Research(grant YSBR006)the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CAS。
文摘We report the discovery of PSR J1909+0122 by the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)as part of the Commensal Radio Astronomy FAST Survey.PSR J1909+0122 has a spin period of 1.257 s and a dispersion measure of 186.2 pc cm^(-3).The averaged pulse profile shows two distinct components.We performed a single-pulse study based on a one-hour observation at 1.25 GHz on 2021 August 23.We used a threshold of 5σ_(ep) to measure the nulling fraction(NF)as 63%±1.5%.The longitude-resolved fluctuation spectra and fast Fourier transform spectra of the binary sequences revealed the quasi-periodicity of nulling with a period of 30 rotation periods.We examined the reliability of the periodicity by comparing it to random noise injection.The NF,E,and modulation periodicity P_(M) of PSR J1909+0122 were compared with other periodic nulling pulsars,showing that the source of J1909+0122 has the second largest NF in the population.Long-term timing observations over six months were used to derive the phase-connected ephemeris of this pulsar.The measured P and P values disfavor dipolar geometry for polar gap models,and the prediction for a space-charge-limited flow model in the case of inverse Compton scattering is only just above the death line.In this work,PSR J1909+0122 has revealed possible correlations between nulling behavior and pulsar properties,which will help to shed light on the pulsar emission mechanism and its temporal evolution in future observations.
基金supported by the National SKA Program of China (Grant No. 2020SKA0120200)the National Natural Science Foundation of China (Grant Nos. 12041303, 12273100, 12041304, and 12288102)+5 种基金the National Key R&D Program of China (Grant No. 2022YFC2205201)the West Light Foundation of the Chinese Academy of Sciences (Grant No. WLFC 2021-XBQNXZ-027)the Major Science and Technology Program of Xinjiang Uygur Autonomous Region (Grant No. 2022A03013-4)the Natural Science Foundation of Xinjiiang Uygur Autonomous Region (Grant No. 2022D01D85)the open program of the Key Laboratory of Xinjiang Uygur Autonomous Region (Grant No. 2020D04049)partly supported by the Operation, Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments, budgeted from the Ministry of Finance of China and administrated by the CAS
文摘We report the results of a search for radio pulsars in five supernova remnants(SNRs)with the FAST telescope.The observations were made using the 19-beam receiver in“snapshot”mode.The integration time for each pointing was 10 min.We discovered a new pulsar,PSR J1845–0306,which has a spin period of 983.6 ms and a dispersion measure of 444.6±2.0 cm^(−3)·pc,in observations of SNR G29.6+0.1.To judge the association between the pulsar and the SNR,further verification is needed.We also re-detected some known pulsars in the data from SNRs G29.6+0.1 and G29.7–0.3.No pulsars were detected in the observations of the other three SNRs.
基金the National Natural Science Foundation of China(NSFC,grant Nos.11988101,11725313,and U1931117)the International Partnership Program of Chinese Academy of Sciences(grant No.114A11KYSB20210010)supported by the Natural Science Foundation of Jiangsu Province(grant No.BK20201108)。
文摘The most extensive survey of carbon monoxide(CO)gas in the Taurus molecular cloud relied on ^(12)CO and ^(13)CO J=1→0 emission only,distinguishing the region where ^(12)CO is detected without ^(13)CO(named mask 1 region)from the one where both are detected(mask 2 region)(Goldsmith et al.2008;Pineda et al.2010).We have taken advantage of recent ^(12)CO J=3→2 James Clerk Maxwell Telescope observations,where they include mask 1regions to estimate density,temperature,and N(CO)with a large velocity gradient model.This represents 1395 pixels out of~1.2 million in the mark 1 region.Compared to Pineda et al.(2010)results and assuming a Tkin of 30 K,we find a higher volume density of molecular hydrogen of 3.3×10^(3) cm^(-3),compared to their 250-700 cm^(-3),and a CO column density of 5.7×10^(15)cm^(-2),about a quarter of their value.The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium.Future observations to extend the ^(12)CO J=3→2 mapping further away from the ^(13)COdetected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.
基金funded by the National Natural Science Foundation of China(NSFC)under NSFC Nos.12373026,11973075,12203091,and 12173075the National Key R&D Program of China under grant No.2022YFA1603103+2 种基金the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China(2022D01A156)the“Tianchi Doctoral Program 2021”supported by the Youth Innovation Promotion Association CAS。
文摘Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood.The protoplanetary disks are the birthplace of planets and its distinctive environment provides an intriguing platform for investigating models of sulfur chemistry.We analyzed the Atacama Large Millimeter/submillimeter Array observations of CS 7-6 transitions in the HD 163296 disk and performed astrochemical modeling to explore its sulfur chemistry.We simulated the distribution of sulfur-containing molecules and compared it with observationally deduced fractional column densities.We have found that the simulated column density of CS is consistent with the observationally deduced fractional column densities,while the simulated column density of C_(2)S is lower than the observationally deduced upper limits on column densities.This results indicate that we have a good understanding of the chemical properties of CS and C_(2)S in the disk.We also investigated the influence of the C/O ratio on sulfur-containing molecules and found that the column densities of SO,SO_(2),and H_2S near the centra star are dependent on the C/O ratio.Additionally,we found that the N[CS]/N[SO]ratio can serve as a promising indicator of the disk’s C/O ratio in HD 163296.Overall,the disk of HD 163296 provides a favorable environmen for the detection of sulfur-containing molecules.
基金supported by the National SKA Program of China(2020SKA0120100,2020SKA0120200)the National Key R&D Program of China(2017YFA0402602)+7 种基金the National Natural Science Foundation of China(NSFC,Grant No.12041303)the CAS-MPG LEGACY project and funding from the Max-Planck Partner Groupsupported by the National Natural Science Foundation of China(NSFC,Grant Nos.11988101 and 11833009)the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSW-SLH021supported by the Cultivation Project for the FAST scientific Payoff and Research Achievement of CAMS-CASsupported by the Key Research Project of Zhejiang Lab no.2021PE0AC0supported by National Natural Science Foundation of China(Grant No.12003028)the China Manned Spaced Project(CMS-CSST-2021-B11)。
文摘As the third paper in the multiple-part series,we report the statistical properties of radio bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode between the 25th and 28th of September 2021(UT).We focus on the polarization properties of536 bright bursts with S/N>50.We found that the Faraday rotation measures(RMs)monotonically dropped from-579to-605 rad m^(-2)in the 4 day window.The RM values were compatible with the values(-300 to-900 rad m^(-2))reported 4 months ago.However,the RM evolution rate in the current observation window was at least an order of magnitude smaller than the one(~500 rad m^(-2)day^(-1))previously reported during the rapid RM-variation phase,but is still higher than the one(≤1 rad m^(-2)day^(-1))during the later RM no-evolution phase.The bursts of FRB 20201124A were highly polarized with the total degree of polarization(circular plus linear)greater than 90%for more than 90%of all bursts.The distribution of linear polarization position angles(PAs),degree of linear polarization(L/I)and degree of circular polarization(V/I)can be characterized with unimodal distribution functions.During the observation window,the distributions became wider with time,i.e.,with larger scatter,but the centroids of the distribution functions remained nearly constant.For individual bursts,significant PA variations(confidence level 5σ)were observed in 33%of all bursts.The polarization of single pulses seems to follow certain complex trajectories on the Poincarésphere,which may shed light on the radiation mechanism at the source or the plasma properties along the path of FRB propagation.
基金supported by the National Natural Science Foundation of China (11988101,11721303,11991052,12011540375,12073002,11903003)the China Manned Space Project (CMS-CSST-2021-A04+3 种基金CMS-CSST-2021-A06)support from the science research grants from the China Manned Space Project with No.CMS-CS ST-2021-B02the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D),through project No.CE170100013support from the Natural Sciences and Engineering Research Council of Canada (NSERC)。
文摘This paper presents data from a 21 cm H I emission drift scan observation of a field partially covering the NGC 4636 galaxy group with the Five-hundred meter Aperture Radio Telescope(FAST). We construct a pipeline to reduce the data, and use So Fi A for source finding. When not contaminated by Radio Frequency Interference(RFI), the FAST observations are capable of detecting all of the galaxies previously detected by the Arecibo Legacy Fast ALFA(ALFALFA) survey in the same region. Comparing to ALFALFA for the detections in common, the FAST data show consistent integrated spectra when the H I disks are spatially unresolved, and capture more flux when the H I disks are resolved. The FAST data further reveal 10 new detections in the region mutually covered with ALFALFA, and 18 new detections beyond the footprint of ALFALFA. All of the new detections have the matching optical counterparts. For the member galaxies of the NGC 4636 group, the detection limit of FAST is deeper by 0.4 dex in H I mass than that of the ALFALFA data. After correcting for the incompleteness caused by RFI contamination, we show that the H I detection rate of galaxies rises steeply with radius out to the virial radius of the group, and flattens beyond that. We also examine four spatially resolved galaxy systems with potential tidal interaction features in detail. Considering that the data have been taken during the“shared-risk” period before a major source of local RFI was eliminated, the results highlight the power of FAST in detecting extragalactic H I.
基金This research was supported by the National Basic Research Program of China （2011CB302600）, the National High Technology Research and Development Program of China （2012AA011201）, the National Natural Science Foundation of China （Grant Nos. 61161160565, 90818028, 91118008, 60903043）, and an NSFC/RGC Joint Research Scheme sponsored by the Research Grants Council of Hong Kong, China and National Natural Science Foundation of China Project （JC201104220300A）.
文摘The growing scale and complexity of component interactions in cloud computing systems post great challenges for operators to understand the characteristics of system performance. Profiling has long been proved to be an effective approach to performance analysis; however, existing approaches confront new challenges that emerge in cloud computing systems. First, the efficiency of the profiling becomes of critical concern; second, service-oriented profiling should be considered to support separation-of-concerns performance analysis. To address the above issues, in this paper, we present P-Tracer, an online performance profiling tool specifically tailored for cloud computing systems. P-Tracer constructs a specific search engine that proactively processes performance logs and generates a particular index for fast queries; second, for each service, P-Tracer retrieves a statistical insight of performance characteristics from multi-dimensions and provides operators with a suite of web-based interfaces to query the critical information. We evaluate P- Tracer in the aspects of tracing overheads, data preprocessing scalability and querying efficiency. Three real-world case studies that happened in Alibaba cloud computing platform demonstrate that P-Tracer can help operators understand soft-ware behaviors and localize the primary causes of performance anomalies effectively and efficiently.
基金supported by the National Natural Science Foundation of China(11988101,12103069,11725313,12273008,12373109,and 12203045)the National Key R&D Program of China(2017YFA0402600 and 2023YFB4503300)+4 种基金the National SKA Program of China(2022SKA0130100 and 2022SKA0130104)the Shandong Provincial Key R&D Program(2022CXGC020106)the Zhejiang Provincial grants(2023R01008 and 2024SSYS0012)Additional support came from the Pilot Project for Integrated Innovation of Science,Education and Industry of Qilu University of Technology(2022JBZ01-01)funding from NextGenerationEU under the Italian PNRR(Project IR0000034 CSTILES)。
文摘Magnetic fields are pervasive throughout the Universe.They are integral to a wide array of astrophysical processes that span various physical scales and field strengths.The Galactic magnetic field,in particular,holds significant importance in shaping the evolution of our Galaxy.However,our understanding of its behavior on small scales remains poor,especially when considering its penetration into the Galactic halo[1].
基金supported by the National SKA Program of China(Grant Nos.2022SKA01102002022SKA0110203)+1 种基金the National Natural Science Foundation of China(Grant Nos.11975072,11835009,11875102,and 11988101)the National 111 Project of China(Grant No.B16009)。
文摘We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We simulate 105and 106localized FRBs from a 10-year SKA observation,and find that:(1)using 106FRB data alone can tightly constrain dark-energy equation of state parameters better than CMB+BAO+SNe,providing an independent cosmological probe to explore dark energy;(2)combining the FRB data with gravitational-wave standard siren data from 10-year observation with the Einstein Telescope,the Hubble constant can be constrained to a sub-percent level,serving as a powerful low-redshift probe;(3)using 106FRB data can constrain the baryon density?bh to a precision of~0.1%.Our results indicate that SKA-era FRBs will provide precise cosmological measurements to shed light on both dark energy and the missing baryon problem,and help resolve the Hubble tension.
基金supported by the National Natural Science Foundation of China (11988101, 12203045, and 11725313)the Key Research Project of Zhejiang Laboratory (2021PE0AC03)+8 种基金the National Key R&D Program of China (2017YFA0402600)supported by the National Natural Science Foundation of China (12003028)the China Manned Spaced Project (CMSCSST-2021-B11)the National Key Research and Development Program of China (2022SKA0130101)the recipient of an Australian Research Council Discovery Early Career Award (DE210101738) funded by the Australian Governmentsupport from the National Natural Science Foundation of China (U2031117)the Youth Innovation Promotion Association CAS (2021055)CAS Project for Young Scientists in Basic Reasearch (grant YSBR-006)the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CAS。
文摘Fast radio bursts(FRBs)are bright millisecond-duration radio transients first discovered by Lorimer et al.[1].While their cosmological origin and energetic naturemake them ideal tools for probing a range of astrophysics[2],their progenitors and radiation mechanisms are still unknown.Aparticularlyinteresting subset of FRBs is the so-called repeating FRBs,which recurrently emit millisecond-duration radio bursts.
