We have carried out the Galactic Plane Pulsar Snapshot(GPPS)survey by using the Five-hundred-meter Aperture Spherical radio Telescope(FAST),the most sensitive systematic pulsar survey in the Galactic plane.In addition...We have carried out the Galactic Plane Pulsar Snapshot(GPPS)survey by using the Five-hundred-meter Aperture Spherical radio Telescope(FAST),the most sensitive systematic pulsar survey in the Galactic plane.In addition to more than 500 pulsars already discovered through normal periodical search,we report here the discovery of 76 new transient radio sources with sporadic strong pulses,detected by using the newly developed module for a sensitive single-pulse search.Their small DM values suggest that they all are Galactic rotating radio transients(RRATs).They show different properties in the follow-up observations.More radio pulses have been detected from 26 transient radio sources but no periods can be found due to a limited small number of pulses from all FAST observations.The followup observations show that 16 transient sources are newly identified as being the prototypes of RRATs with a period already determined from more detected sporadic pulses,and 10 sources are extremely nulling pulsars,and 24 sources are weak pulsars with sparse strong pulses.On the other hand,48 previously known RRATs have been detected by the FAST,either during verification observations for the GPPS survey or through targeted observations of applied normal FAST projects.Except for one RRAT with four pulses detected in a session of 5-minute observation and four RRATs with only one pulse detected in a session,sensitive FAST observations reveal that 43 RRATs are just generally weak pulsars with sporadic strong pulses or simply very nulling pulsars,so that the previously known RRATs always have an extreme emission state together with a normal hardly detectable weak emission state.This is echoed by the two normal pulsars J1938+2213 and J1946+1449 with occasional brightening pulses.Though strong pulses of RRATs are very outstanding in the energy distribution,their polarization angle variations follow the polarization angle curve of the averaged normal pulse profile,suggesting that the predominant sparse pulses of RRATs are emitted in the same region with the same geometry as normal weak pulsars.展开更多
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, ...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.展开更多
This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The st...This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The stability and drift rate of the frequency standard are calculated using 1-year monitoring data.The UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 ns.Pulsar timing observations were carried out for several months.The weighted RMS of timing residuals reaches the level of less than 3.0μs.展开更多
We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being ...We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being mixed with molecular hydrogen H2 and improves our understanding of the atomic to molecular transition in the interstellar medium.HINSA was found in 58%PGCCs that we observed.The column density of HINSA was found to have an intermediate correlation with that of 13CO,following log(N(HINSA))=(0.52±0.26)log(N13CO)+(10±4.1).HI abundance relative to total hydrogen[HI]/[H]has an average value of 4.4×10-3,which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds.For clouds with total column density NH>5×1020 cm-2,an inverse correlation between HINSA abundance and total hydrogen column density is found,confirming the depletion of cold HI gas during molecular gas formation in more massive clouds.Nonthermal line width of 13CO is about 0-0.5 kms-1 larger than that of HINSA.One possible explanation of narrower non-thermal width of HINSA is that HINSA region is smaller than that of 13CO.Based on an analytic model of H2 formation and H2 dissociation by cosmic ray,we found the cloud ages to be within 106.7-107.0 yr for five sources.展开更多
The Five-hundred-meter Aperture Spherical radio Telescope(FAST) has passed national acceptance and finished one pilot cycle of ‘Shared-Risk’ observations. It will start formal operation soon. In this context, this p...The Five-hundred-meter Aperture Spherical radio Telescope(FAST) has passed national acceptance and finished one pilot cycle of ‘Shared-Risk’ observations. It will start formal operation soon. In this context, this paper describes testing results of key fundamental parameters for FAST, aiming to provide basic support for observation and data reduction of FAST for scientific researchers. The 19-beam receiver covering 1.05–1.45 GHz was utilized for most of these observations. The fluctuation in electronic gain of the system is better than 1% over 3.5 hours, enabling enough stability for observations. Pointing accuracy,aperture efficiency and system temperature are three key parameters for FAST. The measured standard deviation of pointing accuracy is 7.9′′, which satisfies the initial design of FAST. When zenith angle is less than 26.4°, the aperture efficiency and system temperature around 1.4 GHz are ~0.63 and less than 24 K for central beam, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral HI observations toward NGC 672 and polarization observations toward 3 C 286. The performance allows FAST to take sensitive observations for various scientific goals, from studies of pulsars to galaxy evolution.展开更多
Radio Frequency Interference(RFI)mitigation is essential for supporting the science output of Five-hundred-meter Aperture Spherical radio Telescope(FAST)due to its high sensitivity.In order to protect FAST from RFI,an...Radio Frequency Interference(RFI)mitigation is essential for supporting the science output of Five-hundred-meter Aperture Spherical radio Telescope(FAST)due to its high sensitivity.In order to protect FAST from RFI,an Electromagnetic Compatibility(EMC)study has been carried out and the operation of a Radio Quiet Zone(RQZ)is ongoing.RFI measurements of the telescope instruments and monitoring of the active radio services outside the site have revealed the radiation properties of the RFI sources.Based on the measurement results and theoretical analysis,various EMC methods have been implemented for the telescope to decrease the RFIs.Meanwhile,the main RFI sources in the FAST RQZ,such as mobile stations,broadcast stations and navigation instruments,have been identified,and the technical measures have been adopted to protect the quiet radio environment around the site.The early science outputs of FAST have demonstrated the efficiency of RFI mitigation methods.展开更多
An active reflector is one of the three main innovations incorporated in the Five-hundredmeter Aperture Spherical radio Telescope(FAST).The deformation of such a huge spherically shaped reflector into different transi...An active reflector is one of the three main innovations incorporated in the Five-hundredmeter Aperture Spherical radio Telescope(FAST).The deformation of such a huge spherically shaped reflector into different transient parabolic shapes is achieved by using 2225 hydraulic actuators which change the position of the 2225 nodes through the connected down tied cables.For each different tracking process of the telescope,more than 1/3 of these 2225 actuators must be in operation to tune the parabolic aperture accurately and meet the surface error restriction.This means that some of these actuators are inevitably located within the main beam of the receiver,and Electromagnetic Interference(EMI)from the actuators must be mitigated to ensure the scientific output of the telescope.Based on the threshold level of interference detrimental to radio astronomy described in ITU-R Recommendation RA.769 and EMI measurements,the shielding efficiency(SE)requirement for each actuator is set to be 80 d B in the frequency range from 70 MHz to 3 GHz.Therefore,Electromagnetic Compatibility(EMC)was taken into account in the actuator design by measures such as power line filters,optical fibers,shielding enclosures and other structural measures.In 2015,all the actuators had been installed at the FAST site.Till now,no apparent EMI from the actuators has been detected by the receiver,which demonstrates the effectiveness of these EMC measures.展开更多
Discovery of pulsars is one of the main goals for large radio telescopes.The Five-hundredmeter Aperture Spherical radio Telescope(FAST),that incorporates an L-band 19-beam receiver with a system temperature of about 2...Discovery of pulsars is one of the main goals for large radio telescopes.The Five-hundredmeter Aperture Spherical radio Telescope(FAST),that incorporates an L-band 19-beam receiver with a system temperature of about 20 K,is the most sensitive radio telescope utilized for discovering pulsars.We designed the snapshot observation mode for a FAST key science project,the Galactic Plane Pulsar Snapshot(GPPS)survey,in which every four nearby pointings can observe a cover of a sky patch of 0.1575 square degrees through beam-switching of the L-band 19-beam receiver.The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes.The goal of the GPPS survey is to discover pulsars within the Galactic latitude of±10∘from the Galactic plane,and the highest priority is given to the inner Galaxy within±5∘.Up to now,the GPPS survey has discovered 201 pulsars,including currently the faintest pulsars which cannot be detected by other telescopes,pulsars with extremely high dispersion measures(DMs)which challenge the currently widely used models for the Galactic electron density distribution,pulsars coincident with supernova remnants,40 millisecond pulsars,16 binary pulsars,some nulling and mode-changing pulsars and rotating radio transients(RRATs).The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars.Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars.The GPPS survey discoveries are published and will be updated at http://zmtt.bao.ac.cn/GPPS/.展开更多
Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the world’s largest single dish radio telescope,which is located in Guizhou Province,in southwest China.The FAST feed cabin is supported and positioned by...Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the world’s largest single dish radio telescope,which is located in Guizhou Province,in southwest China.The FAST feed cabin is supported and positioned by six steel cables.The deviation of the feed position and orientation would lead to loss in the telescope efficiency.In this paper,a series of electromagnetic(EM)simulations of the FAST facility with varying feed positions and orientation offsets was performed.The maximum gain of FAST is about 82.3 dBi and the sibelobe is–32 dB with respect to the main beam at 3 GHz.The simulation results have demonstrated that the telescope efficiency loss is more sensitive to the lateral feed deviation compared with the axial deviation.The telescope efficiency would decrease by 8.2%due to the FAST feed position deviation of 10 mm rms when the observing frequency is 3 GHz.The FAST feed deviation basically has no effect on the sidelobes and cross polarization characteristic according to the simulations.展开更多
This paper describes the design,construction,and performance of the wideband orthomode transducers(OMTs)for the L-(1.2–1.8 GHz),the S-(2–3 GHz)and the P-(0.56–1.12 GHz)band receiver systems of the Five-hundred-mete...This paper describes the design,construction,and performance of the wideband orthomode transducers(OMTs)for the L-(1.2–1.8 GHz),the S-(2–3 GHz)and the P-(0.56–1.12 GHz)band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These OMTs operate at the cryogenic temperature of 70 K to reduce their thermal noise contribution to the receiver chains.The development on the FAST L-and S-band quad-ridged waveguide(QRWG)OMTs is carried out based on the theoretical mode analysis.In view of the miniaturization of FAST cryogenic receiver system at P-band,a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter wavelength.The proposed L-,S-and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator(HFSS),and then manufactured,tested at room temperature.Measurement of FAST cryogenic receiver system noise is also performed with the L-,S-and P-band OMTs installed.The measured results fully comply with the design specifications.展开更多
The kinematics of superluminal components in blazar 3C 454.3 are studied.Nine components are included:superluminal knots R1,R2,R3,R4,A,B,C and D(from Britzen et al.2013) and C4(from Pauliny-Toth 1998).We find that the...The kinematics of superluminal components in blazar 3C 454.3 are studied.Nine components are included:superluminal knots R1,R2,R3,R4,A,B,C and D(from Britzen et al.2013) and C4(from Pauliny-Toth 1998).We find that their kinematics derived from VLBI observations can be consistently interpreted in terms of a jet precession scenario with a period of about 14.5 yr.We discuss the model fits of their trajectory,distance from the core and apparent velocity.We show that the bulk Lorentz factor(in the range 4 to 15) derived for these components does not have any dependence on the phase of the precession(or position angle for ejection).The LenseThirring effect is assumed to interpret the precession of the jet nozzle.The results obtained for blazar 3C 454.3 are only suggestive.They are not unique and have yet to be tested,but they might be useful for understanding the kinematics of superluminal components in blazars and for disentangling different mechanisms and factors.展开更多
The Five-hundred-meter Aperture Sphericalradio Telescope(FAST)willbe the largest radio telescope in the world.The surface tolerance of the main reflector is one of the most important parameters for evaluating the perf...The Five-hundred-meter Aperture Sphericalradio Telescope(FAST)willbe the largest radio telescope in the world.The surface tolerance of the main reflector is one of the most important parameters for evaluating the performance of the telescope. The relationship between the reflector's surface tolerance and the curvature of FAST reflector panels is analyzed and discussed.According to the calculation of reflector tolerance and antenna gain,an optimized panel shape for minimum surface tolerance and maximum gain is derived.The far field pattern of the FAST telescope is presented while the optimized shape is utilized for reflector panels.The results show that FAST could be operated at a frequency band of 8 GHz or even higher with an acceptable efficiency.展开更多
基金This project,as one of five key projects,is being carried out by using FAST,a Chinese national mega-science facility built and operated by the National Astronomical Observatories,Chinese Academy of Sciencessupported by the National Natural Science Foundation of China(NSFC,Nos.11988101 and 11833009)+5 种基金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-CASsupported by NSFC No.12133004,partially supported by NSFC No.U1731120partially supported by the NSFC No.11873058,partially supported by NSFC No.U2031115partially supported by the National SKA program of China No.2020SKA0120200partially supported by the Guangzhou Science and Technology Project No.202102010466。
文摘We have carried out the Galactic Plane Pulsar Snapshot(GPPS)survey by using the Five-hundred-meter Aperture Spherical radio Telescope(FAST),the most sensitive systematic pulsar survey in the Galactic plane.In addition to more than 500 pulsars already discovered through normal periodical search,we report here the discovery of 76 new transient radio sources with sporadic strong pulses,detected by using the newly developed module for a sensitive single-pulse search.Their small DM values suggest that they all are Galactic rotating radio transients(RRATs).They show different properties in the follow-up observations.More radio pulses have been detected from 26 transient radio sources but no periods can be found due to a limited small number of pulses from all FAST observations.The followup observations show that 16 transient sources are newly identified as being the prototypes of RRATs with a period already determined from more detected sporadic pulses,and 10 sources are extremely nulling pulsars,and 24 sources are weak pulsars with sparse strong pulses.On the other hand,48 previously known RRATs have been detected by the FAST,either during verification observations for the GPPS survey or through targeted observations of applied normal FAST projects.Except for one RRAT with four pulses detected in a session of 5-minute observation and four RRATs with only one pulse detected in a session,sensitive FAST observations reveal that 43 RRATs are just generally weak pulsars with sporadic strong pulses or simply very nulling pulsars,so that the previously known RRATs always have an extreme emission state together with a normal hardly detectable weak emission state.This is echoed by the two normal pulsars J1938+2213 and J1946+1449 with occasional brightening pulses.Though strong pulses of RRATs are very outstanding in the energy distribution,their polarization angle variations follow the polarization angle curve of the averaged normal pulse profile,suggesting that the predominant sparse pulses of RRATs are emitted in the same region with the same geometry as normal weak pulsars.
基金supported by the National SKA Program of China (Grant Nos. 2020SKA0120100 and 2020SKA0120200)the National Natural Science Foundation of China (Grant Nos. 12041304, 11873067, 11988101, 12041303, 11725313, 11725314, 11833003, 12003028, 12041306, 12103089, U2031209, U2038105, and U1831207)+8 种基金the National Key Research and Development Program of China (Grant Nos. 2019YFA0405100, 2017YFA0402602, 2018YFA0404204, and 2016YFA0400801)Key Research Program of the Chinese Academy of Sciences (Grant No. QYZDJ-SSW-SLH021)Natural Science Foundation of Jiangsu Province (Grant No. BK20211000)Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CAS, the Strategic Priority Research Program on Space Science, the Western Light Youth Project of Chinese Academy of Sciences (Grant Nos. XDA15360000, XDA15052700, and XDB23040400)funding from the MaxPlanck Partner Group, the science research grants from the China Manned Space Project (Grant Nos. CMS-CSST2021-B11 and CMS-CSST-2021-A11)PKU development (Grant No. 7101502590)support from the XPLORER PRIZEsupported by Fundamental Research Funds for the Central Universities (Grant No. 14380046)the Program for Innovative Talents, Entrepreneur in Jiangsu。
文摘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.
基金supported by the Joint Research Fund in Astronomy(Grant Nos.U1931129,U1631115 and U1831117)under cooperative agreement between NSFC and Chinese Academy of Sciences(CAS)NSFC-STINT Grant 11611130023(CH2015-6360)the National Natural Science Foundation of China(NSFC,Grant No.11403054)
文摘This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The stability and drift rate of the frequency standard are calculated using 1-year monitoring data.The UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 ns.Pulsar timing observations were carried out for several months.The weighted RMS of timing residuals reaches the level of less than 3.0μs.
基金supported by the National Key R&D Program of China(2017YFA0402600 and 2016YFA0400702)the National Natural Science Foundation of China(Grant Nos.11988101,11803051,11725313 and 11721303)+3 种基金CAS International Partnership Program(114A11KYSB20160008)CAS“Light of West China”ProgramCAS Interdisciplinary Innovation Team and Young Researcher Grant of National Astronomical Observatoriessupported in part by the Youth Innovation Promotion Association of CAS(No.2018075)
文摘We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being mixed with molecular hydrogen H2 and improves our understanding of the atomic to molecular transition in the interstellar medium.HINSA was found in 58%PGCCs that we observed.The column density of HINSA was found to have an intermediate correlation with that of 13CO,following log(N(HINSA))=(0.52±0.26)log(N13CO)+(10±4.1).HI abundance relative to total hydrogen[HI]/[H]has an average value of 4.4×10-3,which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds.For clouds with total column density NH>5×1020 cm-2,an inverse correlation between HINSA abundance and total hydrogen column density is found,confirming the depletion of cold HI gas during molecular gas formation in more massive clouds.Nonthermal line width of 13CO is about 0-0.5 kms-1 larger than that of HINSA.One possible explanation of narrower non-thermal width of HINSA is that HINSA region is smaller than that of 13CO.Based on an analytic model of H2 formation and H2 dissociation by cosmic ray,we found the cloud ages to be within 106.7-107.0 yr for five sources.
基金supported by the National Key R & D Program of China (No. 2017YFA0402701)the National Natural Science Foundation of China (NSFC, Nos. 11673039, 11803051 and 11833009)+1 种基金supported by the CAS “Light of West China” programsupported by the Youth Innovation Promotion Association CAS
文摘The Five-hundred-meter Aperture Spherical radio Telescope(FAST) has passed national acceptance and finished one pilot cycle of ‘Shared-Risk’ observations. It will start formal operation soon. In this context, this paper describes testing results of key fundamental parameters for FAST, aiming to provide basic support for observation and data reduction of FAST for scientific researchers. The 19-beam receiver covering 1.05–1.45 GHz was utilized for most of these observations. The fluctuation in electronic gain of the system is better than 1% over 3.5 hours, enabling enough stability for observations. Pointing accuracy,aperture efficiency and system temperature are three key parameters for FAST. The measured standard deviation of pointing accuracy is 7.9′′, which satisfies the initial design of FAST. When zenith angle is less than 26.4°, the aperture efficiency and system temperature around 1.4 GHz are ~0.63 and less than 24 K for central beam, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral HI observations toward NGC 672 and polarization observations toward 3 C 286. The performance allows FAST to take sensitive observations for various scientific goals, from studies of pulsars to galaxy evolution.
基金supported by the National Development and Reform Commission,and the Key Laboratory of FAST of CAS
文摘Radio Frequency Interference(RFI)mitigation is essential for supporting the science output of Five-hundred-meter Aperture Spherical radio Telescope(FAST)due to its high sensitivity.In order to protect FAST from RFI,an Electromagnetic Compatibility(EMC)study has been carried out and the operation of a Radio Quiet Zone(RQZ)is ongoing.RFI measurements of the telescope instruments and monitoring of the active radio services outside the site have revealed the radiation properties of the RFI sources.Based on the measurement results and theoretical analysis,various EMC methods have been implemented for the telescope to decrease the RFIs.Meanwhile,the main RFI sources in the FAST RQZ,such as mobile stations,broadcast stations and navigation instruments,have been identified,and the technical measures have been adopted to protect the quiet radio environment around the site.The early science outputs of FAST have demonstrated the efficiency of RFI mitigation methods.
基金supported by the National Natural Science Foundation of China (No. 11473043)
文摘An active reflector is one of the three main innovations incorporated in the Five-hundredmeter Aperture Spherical radio Telescope(FAST).The deformation of such a huge spherically shaped reflector into different transient parabolic shapes is achieved by using 2225 hydraulic actuators which change the position of the 2225 nodes through the connected down tied cables.For each different tracking process of the telescope,more than 1/3 of these 2225 actuators must be in operation to tune the parabolic aperture accurately and meet the surface error restriction.This means that some of these actuators are inevitably located within the main beam of the receiver,and Electromagnetic Interference(EMI)from the actuators must be mitigated to ensure the scientific output of the telescope.Based on the threshold level of interference detrimental to radio astronomy described in ITU-R Recommendation RA.769 and EMI measurements,the shielding efficiency(SE)requirement for each actuator is set to be 80 d B in the frequency range from 70 MHz to 3 GHz.Therefore,Electromagnetic Compatibility(EMC)was taken into account in the actuator design by measures such as power line filters,optical fibers,shielding enclosures and other structural measures.In 2015,all the actuators had been installed at the FAST site.Till now,no apparent EMI from the actuators has been detected by the receiver,which demonstrates the effectiveness of these EMC measures.
基金This project,as one of five key projects,is being carried out by using FAST,a Chinese national mega-science facility built and operated by the National Astronomical Observatories,Chinese Academy of Sciences.J.L.Han is 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-SSW-SLH021)+4 种基金C.Wang is partially supported by NSFC No.U1731120X.Y.Gao is partially supported by NSFC No.U1831103P.F.Wang is partially supported by the NSFC No.11873058 and the National SKA program of China No.2020SKA0120200.Jun Xu is partially supported by NSFC No.U2031115H.G.Wang is partially supported by the National SKA program of China(No.2020SKA0120100)R.Yuen is partly supported by Xiaofeng Yang's Xinjiang Tianchi Bairen project and CAS Pioneer Hundred Talents Program.L.G.Hou thanks the support from the Youth Innovation Promotion Association CAS.
文摘Discovery of pulsars is one of the main goals for large radio telescopes.The Five-hundredmeter Aperture Spherical radio Telescope(FAST),that incorporates an L-band 19-beam receiver with a system temperature of about 20 K,is the most sensitive radio telescope utilized for discovering pulsars.We designed the snapshot observation mode for a FAST key science project,the Galactic Plane Pulsar Snapshot(GPPS)survey,in which every four nearby pointings can observe a cover of a sky patch of 0.1575 square degrees through beam-switching of the L-band 19-beam receiver.The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes.The goal of the GPPS survey is to discover pulsars within the Galactic latitude of±10∘from the Galactic plane,and the highest priority is given to the inner Galaxy within±5∘.Up to now,the GPPS survey has discovered 201 pulsars,including currently the faintest pulsars which cannot be detected by other telescopes,pulsars with extremely high dispersion measures(DMs)which challenge the currently widely used models for the Galactic electron density distribution,pulsars coincident with supernova remnants,40 millisecond pulsars,16 binary pulsars,some nulling and mode-changing pulsars and rotating radio transients(RRATs).The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars.Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars.The GPPS survey discoveries are published and will be updated at http://zmtt.bao.ac.cn/GPPS/.
基金funded by the National Natural Science Foundation of China(Grant No.11303062)
文摘Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the world’s largest single dish radio telescope,which is located in Guizhou Province,in southwest China.The FAST feed cabin is supported and positioned by six steel cables.The deviation of the feed position and orientation would lead to loss in the telescope efficiency.In this paper,a series of electromagnetic(EM)simulations of the FAST facility with varying feed positions and orientation offsets was performed.The maximum gain of FAST is about 82.3 dBi and the sibelobe is–32 dB with respect to the main beam at 3 GHz.The simulation results have demonstrated that the telescope efficiency loss is more sensitive to the lateral feed deviation compared with the axial deviation.The telescope efficiency would decrease by 8.2%due to the FAST feed position deviation of 10 mm rms when the observing frequency is 3 GHz.The FAST feed deviation basically has no effect on the sidelobes and cross polarization characteristic according to the simulations.
基金supported by Joint Research Fund in Astronomy(U1931129,U1631115 and U1831117)under cooperative agreement between the National Natural Science Foundation of China(NSFC)and the Chinese Academy of SciencesNSFC-STINT Grant of 11611130023(CH2015-6360)the NSFC(Grant Nos.11403054 and 11973006)
文摘This paper describes the design,construction,and performance of the wideband orthomode transducers(OMTs)for the L-(1.2–1.8 GHz),the S-(2–3 GHz)and the P-(0.56–1.12 GHz)band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These OMTs operate at the cryogenic temperature of 70 K to reduce their thermal noise contribution to the receiver chains.The development on the FAST L-and S-band quad-ridged waveguide(QRWG)OMTs is carried out based on the theoretical mode analysis.In view of the miniaturization of FAST cryogenic receiver system at P-band,a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter wavelength.The proposed L-,S-and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator(HFSS),and then manufactured,tested at room temperature.Measurement of FAST cryogenic receiver system noise is also performed with the L-,S-and P-band OMTs installed.The measured results fully comply with the design specifications.
文摘The kinematics of superluminal components in blazar 3C 454.3 are studied.Nine components are included:superluminal knots R1,R2,R3,R4,A,B,C and D(from Britzen et al.2013) and C4(from Pauliny-Toth 1998).We find that their kinematics derived from VLBI observations can be consistently interpreted in terms of a jet precession scenario with a period of about 14.5 yr.We discuss the model fits of their trajectory,distance from the core and apparent velocity.We show that the bulk Lorentz factor(in the range 4 to 15) derived for these components does not have any dependence on the phase of the precession(or position angle for ejection).The LenseThirring effect is assumed to interpret the precession of the jet nozzle.The results obtained for blazar 3C 454.3 are only suggestive.They are not unique and have yet to be tested,but they might be useful for understanding the kinematics of superluminal components in blazars and for disentangling different mechanisms and factors.
基金supported by the Chinese Academy of Sciences and the National Natural Science Foundation of China(Grant No.10433020)
文摘The Five-hundred-meter Aperture Sphericalradio Telescope(FAST)willbe the largest radio telescope in the world.The surface tolerance of the main reflector is one of the most important parameters for evaluating the performance of the telescope. The relationship between the reflector's surface tolerance and the curvature of FAST reflector panels is analyzed and discussed.According to the calculation of reflector tolerance and antenna gain,an optimized panel shape for minimum surface tolerance and maximum gain is derived.The far field pattern of the FAST telescope is presented while the optimized shape is utilized for reflector panels.The results show that FAST could be operated at a frequency band of 8 GHz or even higher with an acceptable efficiency.
