射电天文基础课件

射电天文基础姜碧沩北京师范大学天文系2009/08/24-28日，贵州大学1射电天文基础姜碧沩1EmissionMechanismsofContinuousRadiation

TheNatureofRadioSourcesRadiationfromanAcceleratedElectronTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterTheRadiationofanIonizedGasCloudNonthermalRadiationMechanismsReviewoftheLorentzTransformationTheSynchrotronRadiationofaSingleElectronTheSpectrumandPolarizationofSynchrotronRadiationTheSpectralDistributionofSynchrotronRadiationEnergyRequirementsofSynchrotronSourcesLow-EnergyCutoffsinNonthermalSourcesInverseComptonScattering2009/08/24-28日2射电天文暑期学校EmissionMechanismsofContinuTheNatureofRadioSourcesTwolargefamiliesLocations:galacticandextragalacticSED:ThenatureofdiscretesourceswasinvestigatedbymeasurementsatdifferentfrequenciestodeterminethespectralcharacteristicsRoughlyconstantfluxdensitywithincreasingfrequencyMoreintenseatlowerfrequencyEmissionmechanismsThermalNonthermal2009/08/24-28日3射电天文暑期学校TheNatureofRadioSourcesTwo2009/08/24-28日4射电天文暑期学校2009/08/24-28日4射电天文暑期学校BlackbodyRadiationfromAstronomicalObjectsSolarsystemobjectsSolidbodies,τ=∞Dustinmolecularclouds2.7Kcosmicmicrowavebackground2009/08/24-28日5射电天文暑期学校BlackbodyRadiationfromAstroRadiationfromanAcceleratedElectronθ=π/2pointsinthedirectionofv2009/08/24-28日6射电天文暑期学校RadiationfromanAcceleratedTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterAnelectronmovingpastanionofchargeZe2009/08/24-28日7射电天文暑期学校TheFrequencyDistributionofSpectralEnergyDistribution2009/08/24-28日8射电天文暑期学校SpectralEnergyDistribution20TheRadiationofanIonizedGasCloud2009/08/24-28日9射电天文暑期学校TheRadiationofanIonizedGaEmissionandAbsorptionCoefficients2009/08/24-28日10射电天文暑期学校EmissionandAbsorptionCoeffiEmissionMeasureandOpticalDepth2009/08/24-28日11射电天文暑期学校EmissionMeasureandOpticalDSED2009/08/24-28日12射电天文暑期学校SED2009/08/24-28日12射电天文暑期学校NonthermalRadiationMechanismsRelativisticelectronsmovinginintricately“tangled”magneticfieldsofextendedcoronasbelievedtosurroundcertainkindsofstarsRadiationfromrelativisticcosmicrayelectronsthatmoveinthegeneralinterstellarmagneticfield2009/08/24-28日13射电天文暑期学校NonthermalRadiationMechanismReviewoftheLorentzTransformation2009/08/24-28日14射电天文暑期学校ReviewoftheLorentzTransforVelocity2009/08/24-28日15射电天文暑期学校Velocity2009/08/24-28日15射电天文暑期Acceleration2009/08/24-28日16射电天文暑期学校Acceleration2009/08/24-28日16射电Time2009/08/24-28日17射电天文暑期学校Time2009/08/24-28日17射电天文暑期学校TheSynchrotronRadiationofaSingleElectron2009/08/24-28日18射电天文暑期学校TheSynchrotronRadiationofaTheTotalPowerRadiated2009/08/24-28日19射电天文暑期学校TheTotalPowerRadiated2009/0TheAngularDistributionofRadiation2009/08/24-28日20射电天文暑期学校TheAngularDistributionofRaTheFrequencyDistributionoftheEmission2009/08/24-28日21射电天文暑期学校TheFrequencyDistributionofTheSpectrumandPolarizationofSynchrotronRadiationTheinstantaneousradiationisingeneralellipticallypolarized,butsincethepositionangleofthepolarizationellipseisrotatingwiththeelectron,thetimeaveragedpolarizationislinear.Thisistruealsofortheradiationemittedbyanensembleofmonoenergeticelectronsmovinginparallelorbits.2009/08/24-28日22射电天文暑期学校TheSpectrumandPolarization2009/08/24-28日23射电天文暑期学校2009/08/24-28日23射电天文暑期学校TheSpectralDistributionofSynchrotronRadiationfromanEnsembleofElectrons2009/08/24-28日24射电天文暑期学校TheSpectralDistributionofSHomogeneousMagneticField2009/08/24-28日25射电天文暑期学校HomogeneousMagneticField2009RandomMagneticField2009/08/24-28日26射电天文暑期学校RandomMagneticField2009/08/2EnergyRequirementsofSynchrotronSources2009/08/24-28日27射电天文暑期学校EnergyRequirementsofSynchroLow-EnergyCut-offsinNonthermalSourcesSynchrotronradiationatfrequenciesbelowthelow-frequencycutoffν1shouldhaveaspectralindexofn=1/3Insynchrotronradiationfieldsspontaneousphotonemissionwillbeaccompaniesbyabsorptionandstimulatedemissionasinanyotherradiationfields.Thisabsorptioncanbecomeimportantincompact,high-intensityradiosourcesatlowfrequencieswhentheopticaldepthbecomeslarge.TheRazineffectForegroundthermalplasmamayabsorbmaysynchrotronemissionatlowerfrequencies2009/08/24-28日28射电天文暑期学校Low-EnergyCut-offsinNontherInverseComptonScatteringComptonScatteringAnX-rayorgamma-rayphotoncollideswithaparticle,usuallyanelectron.Someofthephoton’senergyistransferredtotheparticleandthephotonisreradiatedatalongerwavelengthInverseComptonScatteringAlow-energyphotoncollideswithafast-movingelectron.Theelectronpassesonasmallproportionofitsenergytothephoton,thephoton’swavelengthdecreases.Theelectronhastosufferalargenumberofcollisionsbeforeitlosesanappreciablefractionofitsenergy2009/08/24-28日29射电天文暑期学校InverseComptonScatteringCompTheSunyaev-ZeldovichEffectPhotonsfromacoldsource,the2.7Kbackground,interactwithahotforegroundsource,aclusterofgalaxies.SuchclustershavefreeelectronswithTk>107K,sothebremsstrahlungradiationpeaksintheX-rayrange.Theneteffectofaninteractionofthephotonsandelectronsistoshiftlongerwavelengthphotonstoshorterwavelength2009/08/24-28日30射电天文暑期学校TheSunyaev-ZeldovichEffectPhEnergyLossfromHigh-BrightnessSources2009/08/24-28日31射电天文暑期学校EnergyLossfromHigh-BrightneExerciseTheOrionhotcoreisamolecularsourcewithanaveragetemperatureof160K,angularsize10",located500pcfromtheSun.TheaveragelocaldensityofH2is107cm-3.Calculatetheline-of-sightdepthofthisregioninpc,ifthisistakentobethediameterCalculatethecolumndensityN(H2)whichistheintegralofdensityalongtheline-of-sight.AssumethattheregionisuniformObtainthefluxdensityat1.3mmusingTdust=160K,theparameterb=1.9andsolarmetallicityinequation(9.7)UsetheRayleigh-Jeansrelationtoobtainthedustcontinuummainbeambrightnesstemperaturefromthisfluxdensityina10"beam.ShowthatthisismuchsmallerthanTdust.Atlongmillimeterwavelengths,anumberofobservationshaveshownthattheopticaldepthofsuchradiationissmall.ThentheobservedtemperatureisT=Tdustτdust,wherethequantitiesontherighthandsideofthisequationarethedusttemperatureanddustopticaldepth.Fromthisrelationdetermineτdust.Atwhatwavelengthisτdust=1ifτdust~λ-4?2009/08/24-28日32射电天文暑期学校ExerciseTheOrionhotcoreisExerciseFromFig.9.1,determinethe‘turnover’frequencyoftheOrionAHIIregion,thatisthefrequencyatwhichthefluxdensitystopsrisingandstartstodecrease.Thiscanbeobtainedbynotingthefrequencyatwhichthelinearextrapolationofthehighandlowfrequencypartsoftheplotoffluxdensityversusfrequencymeet.Atthispoint,theopticaldepthτffoffree-freeemissionthroughthecenterofOrionAisunity,thatisτff=1,callthisfrequencyν0.Fromequation(9.36)in‘Tools’,therelationofturnoverfrequency,electrontemperatureTeandemissionmeasureEM=Ne2isν0=0.3045(Te)-0.643(EM)0.476.Thisrelationappliestoauniformdensity,uniformtemperatureregion,actualHIIregionshavegradientsinbothquantities,sothisrelationisatbestonlyafirstapproximation.DetermineEMforanelectrontemperatureTe=8300KTheFWHPsizeofOrionAis2.5’,andOrionAis500pcfromtheSun.WhatisthelineardiameterfortheFWHPsize?CombinetheFWHPsizeandemissionmeasuretoobtaintheRMSelectrondensity.2009/08/24-28日33射电天文暑期学校ExerciseFromFig.9.1,determiExerciseThesourceCasAisacloudofionizedgasassociatedwiththeremnantofastarwhichexplodedabout330yearsago.TheradioemissionhastherelationoffluxdensityasafunctionoffrequencyshowninFig.9.1in‘Tools’.Forthesakeofsimplicity,assumethatthesourcehasaconstanttemperatureanddensity,intheshapeofaring,whichthickness1’andouterradiusofangularsize5.5’.Whatistheactualbrightnesstemperatureat100MHz,1GHz,10GHz,100GHz?2009/08/24-28日34射电天文暑期学校ExerciseThesourceCasAisa热和非热射电源的一些例子宁静太阳HII区的射电辐射超新星和超新星遗迹超新星遗迹的流体动力学演化较老的超新星遗迹的射电演化脉冲星河外源2009/08/24-28日35射电天文暑期学校热和非热射电源的一些例子宁静太阳2009/08/24-28宁静太阳太阳射电辐射的检测射电天文史前19世纪末：探测器的低灵敏度20世纪初：观测的停滞Jansky：太阳活动极小年1942年：宁静太阳和活动太阳的射电辐射辐射源日冕热辐射等离子体对低频端的影响非直线的传播逆转的温度结构中频段的临边增亮现象2009/08/24-28日36射电天文暑期学校宁静太阳太阳射电辐射的检测2009/08/24-28日36射HII区的射电辐射HII区OrionA的热辐射轫致辐射距离：450pc两个波段的比较分辨率核的亮温度辐射量度的计算大小简单模型的改进电离星风的射电辐射热辐射非热辐射2009/08/24-28日37射电天文暑期学校HII区的射电辐射HII区OrionA的热辐射2009/0超新星和超新星遗迹超新星分类大质量红巨星的爆发：II型白矮星和的双星系统：I型银河系中发生的频率预计：50年一个已知最近的观测：1606年，Kepler超新星；1667，CasA遗迹的证认形状：展源距离：银河系内天体能谱：与HII区的区别膨胀的壳层与脉冲星成协2009/08/24-28日38射电天文暑期学校超新星和超新星遗迹超新星2009/08/24-28日38射电较老的超新星遗迹的射电演化同步辐射的强度参数的变化磁场强度电子能量谱指数辐射流量的变化CasA的情况2009/08/24-28日39射电天文暑期学校较老的超新星遗迹的射电演化同步辐射的强度2009/08/24超新星遗迹的流体动力学演化自由膨胀阶段被膨胀壳层扫过的气体质量小于初始质量Rt几十年绝热阶段遗迹以被扫荡的物质为主辐射损耗比超新星产生的总能量小得多Rt2/5辐射阶段辐射损耗Rt1/4耗散阶段激波速度降低到声速以下，与星际介质混合2009/08/24-28日40射电天文暑期学校超新星遗迹的流体动力学演化自由膨胀阶段2009/08/24-脉冲星探测和源的本质距离估算和在银河系的分布强度谱和脉冲形状脉冲星定时旋转变慢和磁矩双星脉冲星和毫秒脉冲星射电辐射机制2009/08/24-28日41射电天文暑期学校脉冲星探测和源的本质2009/08/24-28日41射电天文河外源类型AGN：类星体，Seyfert星系，射电星系辐射机制：同步辐射射电星系苏尼阿耶夫－泽尔多维奇效应相对论效应和时变2009/08/24-28日42射电天文暑期学校河外源类型2009/08/24-28日42射电天文暑期学校射电天文基础姜碧沩北京师范大学天文系2009/08/24-28日，贵州大学43射电天文基础姜碧沩1EmissionMechanismsofContinuousRadiation

TheNatureofRadioSourcesRadiationfromanAcceleratedElectronTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterTheRadiationofanIonizedGasCloudNonthermalRadiationMechanismsReviewoftheLorentzTransformationTheSynchrotronRadiationofaSingleElectronTheSpectrumandPolarizationofSynchrotronRadiationTheSpectralDistributionofSynchrotronRadiationEnergyRequirementsofSynchrotronSourcesLow-EnergyCutoffsinNonthermalSourcesInverseComptonScattering2009/08/24-28日44射电天文暑期学校EmissionMechanismsofContinuTheNatureofRadioSourcesTwolargefamiliesLocations:galacticandextragalacticSED:ThenatureofdiscretesourceswasinvestigatedbymeasurementsatdifferentfrequenciestodeterminethespectralcharacteristicsRoughlyconstantfluxdensitywithincreasingfrequencyMoreintenseatlowerfrequencyEmissionmechanismsThermalNonthermal2009/08/24-28日45射电天文暑期学校TheNatureofRadioSourcesTwo2009/08/24-28日46射电天文暑期学校2009/08/24-28日4射电天文暑期学校BlackbodyRadiationfromAstronomicalObjectsSolarsystemobjectsSolidbodies,τ=∞Dustinmolecularclouds2.7Kcosmicmicrowavebackground2009/08/24-28日47射电天文暑期学校BlackbodyRadiationfromAstroRadiationfromanAcceleratedElectronθ=π/2pointsinthedirectionofv2009/08/24-28日48射电天文暑期学校RadiationfromanAcceleratedTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterAnelectronmovingpastanionofchargeZe2009/08/24-28日49射电天文暑期学校TheFrequencyDistributionofSpectralEnergyDistribution2009/08/24-28日50射电天文暑期学校SpectralEnergyDistribution20TheRadiationofanIonizedGasCloud2009/08/24-28日51射电天文暑期学校TheRadiationofanIonizedGaEmissionandAbsorptionCoefficients2009/08/24-28日52射电天文暑期学校EmissionandAbsorptionCoeffiEmissionMeasureandOpticalDepth2009/08/24-28日53射电天文暑期学校EmissionMeasureandOpticalDSED2009/08/24-28日54射电天文暑期学校SED2009/08/24-28日12射电天文暑期学校NonthermalRadiationMechanismsRelativisticelectronsmovinginintricately“tangled”magneticfieldsofextendedcoronasbelievedtosurroundcertainkindsofstarsRadiationfromrelativisticcosmicrayelectronsthatmoveinthegeneralinterstellarmagneticfield2009/08/24-28日55射电天文暑期学校NonthermalRadiationMechanismReviewoftheLorentzTransformation2009/08/24-28日56射电天文暑期学校ReviewoftheLorentzTransforVelocity2009/08/24-28日57射电天文暑期学校Velocity2009/08/24-28日15射电天文暑期Acceleration2009/08/24-28日58射电天文暑期学校Acceleration2009/08/24-28日16射电Time2009/08/24-28日59射电天文暑期学校Time2009/08/24-28日17射电天文暑期学校TheSynchrotronRadiationofaSingleElectron2009/08/24-28日60射电天文暑期学校TheSynchrotronRadiationofaTheTotalPowerRadiated2009/08/24-28日61射电天文暑期学校TheTotalPowerRadiated2009/0TheAngularDistributionofRadiation2009/08/24-28日62射电天文暑期学校TheAngularDistributionofRaTheFrequencyDistributionoftheEmission2009/08/24-28日63射电天文暑期学校TheFrequencyDistributionofTheSpectrumandPolarizationofSynchrotronRadiationTheinstantaneousradiationisingeneralellipticallypolarized,butsincethepositionangleofthepolarizationellipseisrotatingwiththeelectron,thetimeaveragedpolarizationislinear.Thisistruealsofortheradiationemittedbyanensembleofmonoenergeticelectronsmovinginparallelorbits.2009/08/24-28日64射电天文暑期学校TheSpectrumandPolarization2009/08/24-28日65射电天文暑期学校2009/08/24-28日23射电天文暑期学校TheSpectralDistributionofSynchrotronRadiationfromanEnsembleofElectrons2009/08/24-28日66射电天文暑期学校TheSpectralDistributionofSHomogeneousMagneticField2009/08/24-28日67射电天文暑期学校HomogeneousMagneticField2009RandomMagneticField2009/08/24-28日68射电天文暑期学校RandomMagneticField2009/08/2EnergyRequirementsofSynchrotronSources2009/08/24-28日69射电天文暑期学校EnergyRequirementsofSynchroLow-EnergyCut-offsinNonthermalSourcesSynchrotronradiationatfrequenciesbelowthelow-frequencycutoffν1shouldhaveaspectralindexofn=1/3Insynchrotronradiationfieldsspontaneousphotonemissionwillbeaccompaniesbyabsorptionandstimulatedemissionasinanyotherradiationfields.Thisabsorptioncanbecomeimportantincompact,high-intensityradiosourcesatlowfrequencieswhentheopticaldepthbecomeslarge.TheRazineffectForegroundthermalplasmamayabsorbmaysynchrotronemissionatlowerfrequencies2009/08/24-28日70射电天文暑期学校Low-EnergyCut-offsinNontherInverseComptonScatteringComptonScatteringAnX-rayorgamma-rayphotoncollideswithaparticle,usuallyanelectron.Someofthephoton’senergyistransferredtotheparticleandthephotonisreradiatedatalongerwavelengthInverseComptonScatteringAlow-energyphotoncollideswithafast-movingelectron.Theelectronpassesonasmallproportionofitsenergytothephoton,thephoton’swavelengthdecreases.Theelectronhastosufferalargenumberofcollisionsbeforeitlosesanappreciablefractionofitsenergy2009/08/24-28日71射电天文暑期学校InverseComptonScatteringCompTheSunyaev-ZeldovichEffectPhotonsfromacoldsource,the2.7Kbackground,interactwithahotforegroundsource,aclusterofgalaxies.SuchclustershavefreeelectronswithTk>107K,sothebremsstrahlungradiationpeaksintheX-rayrange.Theneteffectofaninteractionofthephotonsandelectronsistoshiftlongerwavelengthphotonstoshorterwavelength2009/08/24-28日72射电天文暑期学校TheSunyaev-ZeldovichEffectPhEnergyLossfromHigh-BrightnessSources2009/08/24-28日73射电天文暑期学校EnergyLossfromHigh-BrightneExerciseTheOrionhotcoreisamolecularsourcewithanaveragetemperatureof160K,angularsize10",located500pcfromtheSun.TheaveragelocaldensityofH2is107cm-3.Calculatetheline-of-sightdepthofthisregioninpc,ifthisistakentobethediameterCalculatethecolumndensityN(H2)whichistheintegralofdensityalongtheline-of-sight.AssumethattheregionisuniformObtainthefluxdensityat1.3mmusingTdust=160K,theparameterb=1.9andsolarmetallicityinequation(9.7)UsetheRayleigh-Jeansrelationtoobtainthedustcontinuummainbeambrightnesstemperaturefromthisfluxdensityina10"beam.ShowthatthisismuchsmallerthanTdust.Atlongmillimeterwavelengths,anumberofobservationshaveshownthattheopticaldepthofsuchradiationissmall.ThentheobservedtemperatureisT=Tdustτdust,wherethequantitiesontherighthandsideofthisequationarethedusttemperatureanddustopticaldepth.Fromthisrelationdetermineτdust.Atwhatwavelengthisτdust=1ifτdust~λ-4?2009/08/24-28日74射电天文暑期学校ExerciseTheOrionhotcoreisExerciseFromFig.9.1,determinethe‘turnover’frequencyoftheOrionAHIIregion,thatisthefrequencyatwhichthefluxdensitystopsrisingandstartstodecrease.Thiscanbeobtainedbynotingthefrequencyatwhichthelinearextrapolationofthehighandlowfrequencypartsoftheplotoffluxdensityversusfrequencymeet.Atthispoint,theopticaldepthτffoffree-freeemissionthroughthecenterofOrionAisunity,thatisτff=1,callthisfrequencyν0.Fromequation(9.36)in‘Tools’,therelationofturnoverfrequency,electrontemperatureTeandemissionmeasureEM=Ne2isν0=0.3045(Te)-0.643(EM)0.476.Thisrelationappliestoauniformdensity,uniformtemperatureregion,actualHIIregionshavegradientsinbothquantities,sothisrelationisatbestonlyafirstapproximation.DetermineEMforanelectrontemperatureTe=8300KTheFWHPsizeofOrionAis2.5’,andOrionAis500pcfromtheSun.Whatisthelineardiamet