射電天文基礎課件

射電天文基礎姜碧溈北京師范大學天文系2009/08/24-28日，貴州大學1射電天文基礎姜碧溈1EmissionMechanismsofContinuousRadiation

TheNatureofRadioSourcesRadiationfromanAcceleratedElectronTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterTheRadiationofanIonizedGasCloudNonthermalRadiationMechanismsReviewoftheLorentzTransformationTheSynchrotronRadiationofaSingleElectronTheSpectrumandPolarizationofSynchrotronRadiationTheSpectralDistributionofSynchrotronRadiationEnergyRequirementsofSynchrotronSourcesLow-EnergyCutoffsinNonthermalSourcesInverseComptonScattering2009/08/24-28日2射電天文暑期學校EmissionMechanismsofContinuTheNatureofRadioSourcesTwolargefamiliesLocations:galacticandextragalacticSED:ThenatureofdiscretesourceswasinvestigatedbymeasurementsatdifferentfrequenciestodeterminethespectralcharacteristicsRoughlyconstantfluxdensitywithincreasingfrequencyMoreintenseatlowerfrequencyEmissionmechanismsThermalNonthermal2009/08/24-28日3射電天文暑期學校TheNatureofRadioSourcesTwo2009/08/24-28日4射電天文暑期學校2009/08/24-28日4射電天文暑期學校BlackbodyRadiationfromAstronomicalObjectsSolarsystemobjectsSolidbodies,τ=∞D(zhuǎn)ustinmolecularclouds2.7Kcosmicmicrowavebackground2009/08/24-28日5射電天文暑期學校BlackbodyRadiationfromAstroRadiationfromanAcceleratedElectronθ=π/2pointsinthedirectionofv2009/08/24-28日6射電天文暑期學校RadiationfromanAcceleratedTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterAnelectronmovingpastanionofchargeZe2009/08/24-28日7射電天文暑期學校TheFrequencyDistributionofSpectralEnergyDistribution2009/08/24-28日8射電天文暑期學校SpectralEnergyDistribution20TheRadiationofanIonizedGasCloud2009/08/24-28日9射電天文暑期學校TheRadiationofanIonizedGaEmissionandAbsorptionCoefficients2009/08/24-28日10射電天文暑期學校EmissionandAbsorptionCoeffiEmissionMeasureandOpticalDepth2009/08/24-28日11射電天文暑期學校EmissionMeasureandOpticalDSED2009/08/24-28日12射電天文暑期學校SED2009/08/24-28日12射電天文暑期學校NonthermalRadiationMechanismsRelativisticelectronsmovinginintricately“tangled”magneticfieldsofextendedcoronasbelievedtosurroundcertainkindsofstarsRadiationfromrelativisticcosmicrayelectronsthatmoveinthegeneralinterstellarmagneticfield2009/08/24-28日13射電天文暑期學校NonthermalRadiationMechanismReviewoftheLorentzTransformation2009/08/24-28日14射電天文暑期學校ReviewoftheLorentzTransforVelocity2009/08/24-28日15射電天文暑期學校Velocity2009/08/24-28日15射電天文暑期Acceleration2009/08/24-28日16射電天文暑期學校Acceleration2009/08/24-28日16射電Time2009/08/24-28日17射電天文暑期學校Time2009/08/24-28日17射電天文暑期學校TheSynchrotronRadiationofaSingleElectron2009/08/24-28日18射電天文暑期學校TheSynchrotronRadiationofaTheTotalPowerRadiated2009/08/24-28日19射電天文暑期學校TheTotalPowerRadiated2009/0TheAngularDistributionofRadiation2009/08/24-28日20射電天文暑期學校TheAngularDistributionofRaTheFrequencyDistributionoftheEmission2009/08/24-28日21射電天文暑期學校TheFrequencyDistributionofTheSpectrumandPolarizationofSynchrotronRadiationTheinstantaneousradiationisingeneralellipticallypolarized,butsincethepositionangleofthepolarizationellipseisrotatingwiththeelectron,thetimeaveragedpolarizationislinear.Thisistruealsofortheradiationemittedbyanensembleofmonoenergeticelectronsmovinginparallelorbits.2009/08/24-28日22射電天文暑期學校TheSpectrumandPolarization2009/08/24-28日23射電天文暑期學校2009/08/24-28日23射電天文暑期學校TheSpectralDistributionofSynchrotronRadiationfromanEnsembleofElectrons2009/08/24-28日24射電天文暑期學校TheSpectralDistributionofSHomogeneousMagneticField2009/08/24-28日25射電天文暑期學校HomogeneousMagneticField2009RandomMagneticField2009/08/24-28日26射電天文暑期學校RandomMagneticField2009/08/2EnergyRequirementsofSynchrotronSources2009/08/24-28日27射電天文暑期學校EnergyRequirementsofSynchroLow-EnergyCut-offsinNonthermalSourcesSynchrotronradiationatfrequenciesbelowthelow-frequencycutoffν1shouldhaveaspectralindexofn=1/3Insynchrotronradiationfieldsspontaneousphotonemissionwillbeaccompaniesbyabsorptionandstimulatedemissionasinanyotherradiationfields.Thisabsorptioncanbecomeimportantincompact,high-intensityradiosourcesatlowfrequencieswhentheopticaldepthbecomeslarge.TheRazineffectForegroundthermalplasmamayabsorbmaysynchrotronemissionatlowerfrequencies2009/08/24-28日28射電天文暑期學校Low-EnergyCut-offsinNontherInverseComptonScatteringComptonScatteringAnX-rayorgamma-rayphotoncollideswithaparticle,usuallyanelectron.Someofthephoton’senergyistransferredtotheparticleandthephotonisreradiatedatalongerwavelengthInverseComptonScatteringAlow-energyphotoncollideswithafast-movingelectron.Theelectronpassesonasmallproportionofitsenergytothephoton,thephoton’swavelengthdecreases.Theelectronhastosufferalargenumberofcollisionsbeforeitlosesanappreciablefractionofitsenergy2009/08/24-28日29射電天文暑期學校InverseComptonScatteringCompTheSunyaev-ZeldovichEffectPhotonsfromacoldsource,the2.7Kbackground,interactwithahotforegroundsource,aclusterofgalaxies.SuchclustershavefreeelectronswithTk>107K,sothebremsstrahlungradiationpeaksintheX-rayrange.Theneteffectofaninteractionofthephotonsandelectronsistoshiftlongerwavelengthphotonstoshorterwavelength2009/08/24-28日30射電天文暑期學校TheSunyaev-ZeldovichEffectPhEnergyLossfromHigh-BrightnessSources2009/08/24-28日31射電天文暑期學校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射電天文暑期學校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射電天文暑期學校ExerciseFromFig.9.1,determiExerciseThesourceCasAisacloudofionizedgasassociatedwiththeremnantofastarwhichexplodedabout330yearsago.TheradioemissionhastherelationoffluxdensityasafunctionoffrequencyshowninFig.9.1in‘Tools’.Forthesakeofsimplicity,assumethatthesourcehasaconstanttemperatureanddensity,intheshapeofaring,whichthickness1’andouterradiusofangularsize5.5’.Whatistheactualbrightnesstemperatureat100MHz,1GHz,10GHz,100GHz?2009/08/24-28日34射電天文暑期學校ExerciseThesourceCasAisa熱和非熱射電源的一些例子寧靜太陽HII區(qū)的射電輻射超新星和超新星遺跡超新星遺跡的流體動力學演化較老的超新星遺跡的射電演化脈沖星河外源2009/08/24-28日35射電天文暑期學校熱和非熱射電源的一些例子寧靜太陽2009/08/24-28寧靜太陽太陽射電輻射的檢測射電天文史前19世紀末：探測器的低靈敏度20世紀初：觀測的停滯Jansky：太陽活動極小年1942年：寧靜太陽和活動太陽的射電輻射輻射源日冕熱輻射等離子體對低頻端的影響非直線的傳播逆轉(zhuǎn)的溫度結(jié)構(gòu)中頻段的臨邊增亮現(xiàn)象2009/08/24-28日36射電天文暑期學校寧靜太陽太陽射電輻射的檢測2009/08/24-28日36射HII區(qū)的射電輻射HII區(qū)OrionA的熱輻射軔致輻射距離：450pc兩個波段的比較分辨率核的亮溫度輻射量度的計算大小簡單模型的改進電離星風的射電輻射熱輻射非熱輻射2009/08/24-28日37射電天文暑期學校HII區(qū)的射電輻射HII區(qū)OrionA的熱輻射2009/0超新星和超新星遺跡超新星分類大質(zhì)量紅巨星的爆發(fā)：II型白矮星和的雙星系統(tǒng)：I型銀河系中發(fā)生的頻率預計：50年一個已知最近的觀測：1606年，Kepler超新星；1667，CasA遺跡的證認形狀：展源距離：銀河系內(nèi)天體能譜：與HII區(qū)的區(qū)別膨脹的殼層與脈沖星成協(xié)2009/08/24-28日38射電天文暑期學校超新星和超新星遺跡超新星2009/08/24-28日38射電較老的超新星遺跡的射電演化同步輻射的強度參數(shù)的變化磁場強度電子能量譜指數(shù)輻射流量的變化CasA的情況2009/08/24-28日39射電天文暑期學校較老的超新星遺跡的射電演化同步輻射的強度2009/08/24超新星遺跡的流體動力學演化自由膨脹階段被膨脹殼層掃過的氣體質(zhì)量小于初始質(zhì)量Rt幾十年絕熱階段遺跡以被掃蕩的物質(zhì)為主輻射損耗比超新星產(chǎn)生的總能量小得多Rt2/5輻射階段輻射損耗Rt1/4耗散階段激波速度降低到聲速以下，與星際介質(zhì)混合2009/08/24-28日40射電天文暑期學校超新星遺跡的流體動力學演化自由膨脹階段2009/08/24-脈沖星探測和源的本質(zhì)距離估算和在銀河系的分布強度譜和脈沖形狀脈沖星定時旋轉(zhuǎn)變慢和磁矩雙星脈沖星和毫秒脈沖星射電輻射機制2009/08/24-28日41射電天文暑期學校脈沖星探測和源的本質(zhì)2009/08/24-28日41射電天文河外源類型AGN：類星體，Seyfert星系，射電星系輻射機制：同步輻射射電星系蘇尼阿耶夫－澤爾多維奇效應相對論效應和時變2009/08/24-28日42射電天文暑期學校河外源類型2009/08/24-28日42射電天文暑期學校射電天文基礎姜碧溈北京師范大學天文系2009/08/24-28日，貴州大學43射電天文基礎姜碧溈1EmissionMechanismsofContinuousRadiation

TheNatureofRadioSourcesRadiationfromanAcceleratedElectronTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterTheRadiationofanIonizedGasCloudNonthermalRadiationMechanismsReviewoftheLorentzTransformationTheSynchrotronRadiationofaSingleElectronTheSpectrumandPolarizationofSynchrotronRadiationTheSpectralDistributionofSynchrotronRadiationEnergyRequirementsofSynchrotronSourcesLow-EnergyCutoffsinNonthermalSourcesInverseComptonScattering2009/08/24-28日44射電天文暑期學校EmissionMechanismsofContinuTheNatureofRadioSourcesTwolargefamiliesLocations:galacticandextragalacticSED:ThenatureofdiscretesourceswasinvestigatedbymeasurementsatdifferentfrequenciestodeterminethespectralcharacteristicsRoughlyconstantfluxdensitywithincreasingfrequencyMoreintenseatlowerfrequencyEmissionmechanismsThermalNonthermal2009/08/24-28日45射電天文暑期學校TheNatureofRadioSourcesTwo2009/08/24-28日46射電天文暑期學校2009/08/24-28日4射電天文暑期學校BlackbodyRadiationfromAstronomicalObjectsSolarsystemobjectsSolidbodies,τ=∞D(zhuǎn)ustinmolecularclouds2.7Kcosmicmicrowavebackground2009/08/24-28日47射電天文暑期學校BlackbodyRadiationfromAstroRadiationfromanAcceleratedElectronθ=π/2pointsinthedirectionofv2009/08/24-28日48射電天文暑期學校RadiationfromanAcceleratedTheFrequencyDistributionofBremsstrahlungforanIndividualEncounterAnelectronmovingpastanionofchargeZe2009/08/24-28日49射電天文暑期學校TheFrequencyDistributionofSpectralEnergyDistribution2009/08/24-28日50射電天文暑期學校SpectralEnergyDistribution20TheRadiationofanIonizedGasCloud2009/08/24-28日51射電天文暑期學校TheRadiationofanIonizedGaEmissionandAbsorptionCoefficients2009/08/24-28日52射電天文暑期學校EmissionandAbsorptionCoeffiEmissionMeasureandOpticalDepth2009/08/24-28日53射電天文暑期學校EmissionMeasureandOpticalDSED2009/08/24-28日54射電天文暑期學校SED2009/08/24-28日12射電天文暑期學校NonthermalRadiationMechanismsRelativisticelectronsmovinginintricately“tangled”magneticfieldsofextendedcoronasbelievedtosurroundcertainkindsofstarsRadiationfromrelativisticcosmicrayelectronsthatmoveinthegeneralinterstellarmagneticfield2009/08/24-28日55射電天文暑期學校NonthermalRadiationMechanismReviewoftheLorentzTransformation2009/08/24-28日56射電天文暑期學校ReviewoftheLorentzTransforVelocity2009/08/24-28日57射電天文暑期學校Velocity2009/08/24-28日15射電天文暑期Acceleration2009/08/24-28日58射電天文暑期學校Acceleration2009/08/24-28日16射電Time2009/08/24-28日59射電天文暑期學校Time2009/08/24-28日17射電天文暑期學校TheSynchrotronRadiationofaSingleElectron2009/08/24-28日60射電天文暑期學校TheSynchrotronRadiationofaTheTotalPowerRadiated2009/08/24-28日61射電天文暑期學校TheTotalPowerRadiated2009/0TheAngularDistributionofRadiation2009/08/24-28日62射電天文暑期學校TheAngularDistributionofRaTheFrequencyDistributionoftheEmission2009/08/24-28日63射電天文暑期學校TheFrequencyDistributionofTheSpectrumandPolarizationofSynchrotronRadiationTheinstantaneousradiationisingeneralellipticallypolarized,butsincethepositionangleofthepolarizationellipseisrotatingwiththeelectron,thetimeaveragedpolarizationislinear.Thisistruealsofortheradiationemittedbyanensembleofmonoenergeticelectronsmovinginparallelorbits.2009/08/24-28日64射電天文暑期學校TheSpectrumandPolarization2009/08/24-28日65射電天文暑期學校2009/08/24-28日23射電天文暑期學校TheSpectralDistributionofSynchrotronRadiationfromanEnsembleofElectrons2009/08/24-28日66射電天文暑期學校TheSpectralDistributionofSHomogeneousMagneticField2009/08/24-28日67射電天文暑期學校HomogeneousMagneticField2009RandomMagneticField2009/08/24-28日68射電天文暑期學校RandomMagneticField2009/08/2EnergyRequirementsofSynchrotronSources2009/08/24-28日69射電天文暑期學校EnergyRequirementsofSynchroLow-EnergyCut-offsinNonthermalSourcesSynchrotronradiationatfrequenciesbelowthelow-frequencycutoffν1shouldhaveaspectralindexofn=1/3Insynchrotronradiationfieldsspontaneousphotonemissionwillbeaccompaniesbyabsorptionandstimulatedemissionasinanyotherradiationfields.Thisabsorptioncanbecomeimportantincompact,high-intensityradiosourcesatlowfrequencieswhentheopticaldepthbecomeslarge.TheRazineffectForegroundthermalplasmamayabsorbmaysynchrotronemissionatlowerfrequencies2009/08/24-28日70射電天文暑期學校Low-EnergyCut-offsinNontherInverseComptonScatteringComptonScatteringAnX-rayorgamma-rayphotoncollideswithaparticle,usuallyanelectron.Someofthephoton’senergyistransferredtotheparticleandthephotonisreradiatedatalongerwavelengthInverseComptonScatteringAlow-energyphotoncollideswithafast-movingelectron.Theelectronpassesonasmallproportionofitsenergytothephoton,thephoton’swavelengthdecreases.Theelectronhastosufferalargenumberofcollisionsbeforeitlosesanappreciablefractionofitsenergy2009/08/24-28日71射電天文暑期學校InverseComptonScatteringCompTheSunyaev-ZeldovichEffectPhotonsfromacoldsource,the2.7Kbackground,interactwithahotforegroundsource,aclusterofgalaxies.SuchclustershavefreeelectronswithTk>107K,sothebremsstrahlungradiationpeaksintheX-rayrange.Theneteffectofaninteractionofthephotonsandelectronsistoshiftlongerwavelengthphotonstoshorterwavelength2009/08/24-28日72射電天文暑期學校TheSunyaev-ZeldovichEffectPhEnergyLossfromHigh-BrightnessSources2009/08/24-28日73射電天文暑期學校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射電天文暑期學校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