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Extragalactic dispersion measures of fast radio bursts

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Research in Astronomy and Astrophysics 2015年第10期15卷 1629-1638页

作者： jun Xu j.l.han National Astronomical Observatories Chinese Academy of Sciences

Fast radio bursts show large dispersion measures, much larger than the Galactic dispersion measure foreground. Therefore, they evidently have an extragalac- tic origin. We investigate possible contributions to the dispersion measure from host galaxies. We simulate the spatial distribution of fast radio bursts and calculate the dis- persion measures along the sightlines from fast radio bursts to the edge of host galaxies by using the scaled NE2001 model for thermal electron density distributions. We find that contributions to the dispersion measure of fast radio bursts from the host galaxy follow a skew Gaussian distribution. The peak and the width at half maximum of the dispersion measure distribution increase with the inclination angle of a spiral galaxy, to large values when the inclination angle is over 70~. The largest dispersion measure produced by an edge-on spiral galaxy can reach a few thousand pc cm-3, while the dispersion measures from dwarf galaxies and elliptical galaxies have a maximum of only a few tens of pc cm-3. Notice, however, that additional dispersion measures of tens to hundreds of pc cm-3 can be produced by high density clumps in host galaxies. Simulations that include dispersion measure contributions from the large Magellanic Cloud and the Andromeda Galaxy are shown as examples to demonstrate how to ex- tract the dispersion measure from the intergalactic medium.

关键词： galaxies: ISM -- radio continuum: ISM -- ISM: general

Cleaning Radio Frequency Interference in Pulsar-Folded Data Based on the Conditional Random Fields with an Adaptive Prior

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Research in Astronomy and Astrophysics 2023年第10期23卷 184-191页

作者： Xue Chen j.l.han W.Q.Su Z.l.Yang D.j.Zhou National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China CAS Key laboratory of FAST NAOCChinese Academy of SciencesBeijing 100101China

Radio astronomy observations are frequently impacted by radio frequency interference(RFI).We propose a novel method,named 2σCRF,for cleaning RFI in the folded data of pulsar observations,utilizing a Bayesian-based model called conditional random fields(CRFs).This algorithm minimizes the“energy”of every pixel given an initial *** standard deviations(i.e.,rms values)of the folded pulsar data are utilized as pixels for all subintegrations and ***-RFI data without obvious interference is treated as“background noise,”while RFI-affected data have different classes due to their exceptional rms *** initial labeling can be automated and is adaptive to the actual *** CRF algorithm optimizes the label category for each pixel of the image with the prior initial *** demonstrate the efficacy of the proposed method on pulsar folded data obtained from Five-hundred-meter Aperture Spherical radio Telescope *** can effectively recognize and tag various categories of RFIs,including broadband or narrowband,constant or instantaneous,and even weak RFIs that are unrecognizable in some pixels but picked out based on their *** results are comparable to those obtained via manual labeling but without the need for human intervention,saving time and effort.

关键词： methods:data analysis techniques:image processing (stars:)pulsars:general

A New Emission Mode of PSR B1859+07

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Research in Astronomy and Astrophysics 2023年第10期23卷 176-183页

作者： Tao Wang P.F.Wang j.l.han Yi Yan Ye-Zhao Yu Feifei Kou National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China The key laboratory for Radio Astronomy and Technology Chinese Academy of SciencesBeijing 100101China Qiannan Normal University for Nationalities Duyun 558000China Xinjiang Astronomical Observatories Chinese Academy of SciencesUrumqi 830011China

Previous studies have identified two emission modes in PSR B1859+07: a normal mode that has three prominent components in the average profile, with the trailing one being the brightest, and an anomalous mode(i.e., the A mode) where emissions seem to be shifted to an earlier phase. Within the normal mode, further analysis has revealed the presence of two submodes, i.e., the cW mode and c B mode, where the central component can appear either weak or bright. As for the anomalous mode, a new bright component emerges in the advanced phase while the bright trailing component in the normal mode disappears. New observations of PSR B1859+07 using the Fivehundred-meter Aperture Spherical Radio Telescope(FAST) have revealed the existence of a previously unknown emission mode, dubbed the Af mode. In this mode, all emission components seen in the normal and anomalous modes are detected. Notably, the mean polarization profiles of both the A and Af modes exhibit a jump in the orthogonal polarization angle modesin the bright leading component. The polarization angles for the central component in the original normal mode follow two distinct orthogonal polarization modes in the A and Af modes respectively. The polarization angles for the trailing component show almost the same but a small systematic shift in the A and Af modes, roughly following the values for the c W and cB modes. Those polarization features of this newly detected emission mode imply that the anomalous mode A of PSR B1859+07 is not a result of “phase shift”or “swooshes” of normal components, but simply a result of the varying intensities of different profile ***, subpulse drifting has been detected in the leading component of the Af mode.

关键词： (stars:)pulsars:individual(PSR B1859+07) polarization plasmas

Three New Spiral Galaxies with Active Nuclei Producing Double Radio lobes

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Research in Astronomy and Astrophysics 2023年第3期23卷 46-53页

作者： X.Y.Gao Z.S.Yuan j.l.han Z.l.Wen S.S.Shan National Astronomical Observatories Chinese Academy of SciencesBejing 10011China CAS Key laboratory of FAST National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy University of Chinese Academy of SciencesBeijing 100049China

Double radio lobes are generally believed to be produced by active nuclei of elliptical ***,several double-lobed radio sources have been solidly found to be associated with spiral *** cross-matching~9×105 spiral galaxies selected from the Sloan Digital Sky Survey DR8 data with the full 1.4 GHz radio source catalogs of NRAO VlA Sky Survey and Faint Images of the Radio Sky at Twenty-centimeters,we identify three new spiral galaxies:j0326-0623,j1110+0321 and j1134+3046 that produce double radio lobes,and five doublelobed spirals previously *** combining the newly discovered and all the other known cases in literature,we confirm the relation that more massive spiral galaxies could produce more powerful radio *** find that most of these spiral galaxies are located in a galaxy group or a poor cluster,in which the environment is denser than in the field,and about half of them are the central brightest galaxies in their parent *** therefore suggest that the environment is one of the key factors for a spiral to produce double radio lobes.

关键词： galaxies galaxy massive

SARS-CoV-2肺炎的CT特征与临床表现:对武汉120例病人的回顾性分析

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国际医学放射学杂志 2020年第5期 627-628页

作者： R.Zhang H.Q.Ouyang l.l.Fu S.j.Wang j.l.han K.j.Huang 霍萌 Cancer Center Renmin Hospital of Wuhan University

摘要目的根据临床严重程度探讨重症急性呼吸综合征冠状病毒2(SARS-CoV-2)病人的胸部CT的特征性表现,分别比较普通病例和重症病例、有症状和无症状病人以及高

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FAST Pulsar *** Profiles of 682 Pulsars

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Research in Astronomy and Astrophysics 2023年第10期23卷 71-175页

作者： P.F.Wang j.l.han j.Xu C.Wang Y.Yan W.C.jing W.Q.Su D.j.Zhou T.Wang National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy University of Chinese Academy of SciencesBeijing 100049China

Pulsar polarization profiles form a very basic database for understanding the emission processes in a pulsar *** careful polarization calibration of the 19-beam l-band receiver and verification of beamoffset observation results,we obtain polarization profiles of 682 pulsars from observations by the Five-hundredmeter Aperture Spherical radio Telescope(FAST)duringthe Galactic Plane Pulsar Snapshot survey and other normal FAST *** them,polarization profiles of about 460 pulsars are observed for the first *** profiles exhibit diverse *** pulsars have a polarization position angle curve with a good S-shaped swing,some with orthogonal modes;some have components with highly linearly polarized components or strong circularly polarized components;some have a very wide profile,coming from an aligned rotator,and some have an interpulse from a perpendicular rotator;some wide profiles are caused by interstellar *** derive geometric parameters for 190 pulsars from the S-shaped position angle curves or with orthogonal *** find that the linear and circular polarization or the widths of pulse profiles have various frequency *** with a large fraction of linear polarization are more likely to have a large Edot.

关键词： polarization (stars:)pulsars:general astronomical databases:miscellaneous

FAST Observations of an Extremely Active Episode of FRB 20201124A:Ⅰ.Burst Morphology

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Research in Astronomy and Astrophysics 2022年第12期22卷 54-69页

作者： D.j.Zhou j.l.han B.Zhang K.j.lee W.W.Zhu D.li W.C.jing W.-Y.Wang Y.K.Zhang j.C.jiang j.R Niu R luo H.Xu C.F.Zhang B.j.Wang j.W.Xu P.Wang Z.l.Yang Y.Feng National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy University of Chinese Academy of SciencesBeijing 100049China CAS Key laboratory of FAST NAOCChinese Academy of SciencesBeijing 100101China Department of Physics and Astronomy University of NevadaLas VegasNV 89154USA Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy Peking UniversityBeijing 100871China CSIRO Space and Astronomy EppingNSW 1710Australia Research Center for Intelligent Computing Platforms Zhejiang LaboratoryHangzhou 311100China

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 *** observations were carried out in the band of 1.0–1.5 GHz by using the center beam of the l-band 19-beam *** monitored the source in sixteen1 hr sessions and one 3 hr session spanning 23 *** the bursts were detected during the first four *** 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 *** duration of a burst is therefore always longer than 1 ms,with the longest up to more than 120 *** emission spectra of the sub-bursts are typically narrow within the observing band with a characteristic width of~277 *** center frequency distribution has a dominant peak at about 1091.9 MHz and a secondary weak peak around 1327.9 *** bursts show a frequencydownwarddrifting *** 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)*** 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.

关键词： (stars:)pulsars:general Physical Data and Processes stars:individual(FRB 20201124A)

Novel medium entropy perovskite oxide Sr(FeCoNiMo)_(1/4)O_(3−δ)for zinc-air battery cathode

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journal of Energy Chemistry 2024年第9期96卷 669-678页

作者： Kaixin li juntao Gao Xu han Qi Shao Zhe lü School of Physics Harbin Institute of TechnologyHarbin 150001HeilongjiangChina Heilongjiang Provincial Key laboratory of Advanced Quantum Functional Materials and Sensor Components Harbin 150001HeilongjiangChina

It is widely recognized that the development of ZABs is impeded by the kinetic bottleneck of oxygen evolution reaction(OER)and oxygen reduction reaction(ORR).The application of conformational entropy strategy to oxides often involves introducing multiple elements with different properties,thereby providing outstanding bifunctional catalytic activity for OER/***,the possible underlying catalytic pathways and potential interactions between various components are still poorly *** paper presents an excellent medium-entropy perovskite oxide,Sr(FeCoNiMo)_(1/4)O_(3−δ)(lower overpotential of 301 mV at 10 mA cm^(−2)).Zinc-air batteries employing it as a cathode catalyst demonstrate excellent round-trip efficiency(62%).By combining theoretical calculation with experiments,we aim to establish the link between the electronic structure of perovskite oxides with different elemental compositions and their OER *** reveals that the conformational entropy strategy can simultaneously shift the O 2p-band center and metal d-band center of perovskite oxide towards the vicinity of the Fermi energy level,thereby triggering a more favorable lattice oxygen-participated mechanism(lOM)during the OER *** outcomes of this work provide crucial insights into the role of conformational entropy strategies in oxygen catalysis and offer potential avenues for constructing efficient and stable electrocatalysts.

关键词： Sr(FeCoNiMo)_(1/4)O_(3−δ) Bifunctional catalyst Medium entropy lOM Rechargeable zinc-air batteries

The FAST Galactic Plane Pulsar Snapshot survey:*** design and pulsar discoveries

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Research in Astronomy and Astrophysics 2021年第5期21卷 5-42页

作者： j.l.han Chen Wang P.F.Wang Tao Wang D.j.Zhou jing-Hai Sun Yi Yan Wei-Qi Su Wei-Cong jing Xue Chen X.Y.Gao li-Gang Hou jun Xu K.j.lee Na Wang Peng jiang Ren-Xin Xu jun Yan Heng-Qian Gan Xin Guan Wen-jun Huang jin-Chen jiang Hui li Yun-Peng Men Chun Sun Bo-jun Wang H.G.Wang Shuang-Qiang Wang jin-Tao Xie Heng Xu Rui Yao Xiao-Peng You D.j.Yu jian-Ping Yuan Rai Yuen Chun-Feng Zhang Yan Zhu National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China CAS Key laboratory of FAST NAOCChinese Academy of SciencesBeijing 100101China School of Astronomy University of Chinese Academy of SciencesBeijing 100049China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy Peking UniversityBeijing 100871China Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China Key laboratory of Radio Astronomy Chinese Academy of SciencesNanjing 210008China Department of Astronomy Guangzhou UniversityGuangzhou 510006China School of Physical Science and Technology Southwest UniversityChongqing 400715China

Discovery of pulsars is one of the main goals for large radio *** 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 *** 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 *** integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 *** 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 ***-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 *** GPPS survey discoveries are published and will be updated at http://***/GPPS/.

关键词： pulsars:general