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 3C 286. The performance allows FAST to take sensitive observations for various scientific goals, from studies of pulsars to galaxy evolution.
Abstract
Discovery of pulsars is one of the main goals for large radio telescopes. The Five-hundred-meter 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/
.
Abstract
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 follow-up 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.
RFI measurements and mitigation for FAST Zhang, Hai-Yan; Wu, Ming-Chang; Yue, You-Ling ...
Research in astronomy and astrophysics,
05/2020, Letnik:
20, Številka:
5
Journal Article
Recenzirano
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.
Five-hundred-meter Aperture radio Spherical 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.
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 (N(HINSA)) = (0.52 ± 0.26) (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. Non-thermal line width of 13CO is about 0-0.5 km s−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.
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 70K 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.
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 3.0 μs.
EMC design for actuators in the FAST reflector Zhang, Hai-Yan; Wu, Ming-Chang; Yue, You-Ling ...
Research in astronomy and astrophysics,
04/2018, Letnik:
18, Številka:
4
Journal Article
Recenzirano
Odprti dostop
An active reflector is one of the three main innovations incorporated in the Five-hundred-meter 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 dB 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.
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
.
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