19 69ApJ. . . 157 IK a 1 The AstrophysicalJournal,Vol.157,July1969 probably distantgalaxies. of self-absorption,bytheirspatialdistribution.Sourcesidentifiedwithquasi-stellarobjectshaveawider Catalogue atfrequenciesof38,178,750,1400,2695,and5000MHz.Thesehavebeenusedtodetermine urement offluxdensity,byuncertaintiesinthecalibrationflux-densityscalesat many sourcesisdeterminednotonlybytheenergydistributionofrelativisticelectronsbutalso,asaresult the spectrumofeachsourceoverthisfrequencyrange.Itisconcludedthatformspectrain (c) 1969.TheUniversityofChicago.Allrightsreserved.PrintedinU.S.A. where theredshiftsand,therefore,distanceswere known,theintrinsicallystronger made absolutebycomparingthesecalibrationsourceswiththeprimarystandard lating theobservationstoasmallnumberofcalibrationsources.Thisscalewasthen different frequencies,andbythelimitedrangeoffrequenciescovered.About5years quencies. Amongtheradiogalaxies,intrinsicallystrongestsourcesappeartohavesteepestspectra. dispersion ofspectralindicesthanthoseidentifiedwithradiogalaxies,particularlyatthehigherfre- median valueof—0.71andadispersion0.15. Foridentifiedextragalacticsources 38 and3200MHz(Conway,Kellermann,Long1963,hereinafterreferredtoas improved theaccuracyofflux-densitymeasurementsandsomadeitpossibletoobtain Unidentified sourceshavesteepspectrasimilartothoseofthestrongerradiogalaxies,andtheyare curvature wassomarkedthatthefluxdensity foundtoshowamaximumwithin law andbecamesignificantlysteeperasthefrequency increased.Inafewcasesthe sources includedshowedaconsiderablylargerdispersion ofspectralindices. range offrequencies. source, CasA,forwhichabsoluteflux-densitymeasurementswereavailableovera reasonably accuratespectrafor160sourcesoverawiderangeoffrequenciesbetween ago observationswithlargeinstrumentsatCambridge,Caltech,andJodrellBank sources werefoundontheaveragetohaveaslightly steeperspectrum.Thegalactic simple powerlaw,Sv,whereaisthespectral index. CKL). Auniformflux-densityscalewasestablishedbyCKLatallfrequenciesre- v 1 a © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Accurate valuesofthefluxdensityaregivenfornearlyallsourcesinRevisedThirdCambridge Early studiesofthespectraradiosourceswerelimitedbyuncertaintiesinmeas- The mostimportantresultsoftheCKLstudywerefollowing: c) Thespectraofanumbersourcesdeviated considerably fromasimplepower b) Theextragalacticsourcesincludedhadanarrow rangeofspectralindiceswitha CKLandsomeotherauthors definethespectralindexabypowerlaw,Scc.~. a) Forthemajorityofsources,fluxdensityS atfrequencyvwasgivenbythe * OperatedbyAssociatedUniversities, Inc.,undercontractwiththeNationalScience Foundation. t Presentaddress:AdranFfiseg, ColegPrifysogolCymru,Aberystwyth,Wales. v v National RadioAstronomyObservatory,*GreenBank,WestVirginia K. I.Kellermannand1.1.Pauliny-Toth THE SPECTRAOFRADIOSOURCESIN Received October14,1968;revisedDecember16,1968 Cavendish Laboratory,Cambridge,England THE REVISED3CCATALOGUE P. J.S.Williamsf I. INTRODUCTION ABSTRACT AND 1 19 69ApJ. . . 157 IK íí, 2 errors duetotheinclusion ofdifferentcomponentsatfrequencies. frequencies. Thishasgreatly improvedthehomogeneityofdataand minimized noise isnotalimitingfactor. been usedintheinterpretationofobservationsmade withlessresolutionatthelower indices aretobemeaningful.Inthepresentstudy thevariousParkescatalogues,4C sis iscompleteabovealimitingfluxdensityof5.0f.u.atsurveyfrequency178 measured atfrequenciesbetween38and1410MHz(Longetal.1966;Williams south ofdeclination+20°atfrequencies408,1410,and2650MHz,theanalysis catalogue, andtheNRAOcatalogue(Pauliny-Toth, Wade,andHeeschen1966)have clearly itmustbethesameatdifferentfrequencies ifrelativefluxdensitiesorspectral quencies havebeenmadewithdifferentresolutions. Inreportingfluxdensitiesobtained separated components.Thisisespeciallytrueif the observationsatdifferentfre- low-noise amplifiersathighfrequencies,sothatformostofthesourcesradiometer be morereliablethananypreviouslypublishedvalues.Thisisdueinparttotheuseof data arethereforewellsuitedbothforstatisticalinvestigationandthedetailedstudy vised 3Ccatalogue(apartfromafewextendedsourcesnearthegalacticplane),and to beconsideredpartofthesourceinquestion. Oftenthechoiceisarbitrary,but of individualspectra.Ateachfrequencythefluxdensitiesgivenherearethoughtto sources inseveralrespects.FluxdensitieshavenowbeenmeasuredatCambridgeor 2.0 f.u.at178MHz,4.0408and2.5610MHz.Themainpurposeof Stewart 1967;Williamsetal.1968)Overthewholerangeofdeclinationsanaly- and Milne1965;Dayetal.1966;Shimmins1966).Thiscoverssome2000sources observed fringeamplitudes. at differentfrequencies,observersoftendifferin determiningwhichcomponentsare the uncertaintyinfluxdensityofextendedsources containingtwoormorespatially the NRAOat38,178,750,1400,2695,and5000MHzfornearlyallsourcesinre- sources fromthe4Ccatalogueindeclinationrange0°to+44°,usingfluxdensities is completeabovealimitingfluxdensityof4f.u.atthesurveyfrequency408MHz. were madewithinterferometersofmoderatespacing,anderrorsintroducedin unresolved weakersourcesintheantennabeam.Moreover,manyofobservations limit athighfrequencies.Second,thelowprimaryresolutionseveraloffre- emphasis wasgiventothedetailedanalysisofindividualspectra. of frequenciescoveredislimitedanditdifficulttodrawdefiniteconclusionsabout The numberofsourcesstudiedatParkesismuchgreaterthaninCKL,buttherange with steepspectrabecausethefluxdensitiesofsuchsourcesfellbelowsomeill-defined low-frequency survey,butonlythosesourceswhichwerestrongenoughtobeobserved incomplete andsubjecttostrongselectioneffects.Thesourceswereselectedfroma spectral curvaturefrommeasurementsatonlythreefrequencies. the 210-foottelescopeatParkes,Australia(Bolton,Gardner,andMackey1964;Price some casesbytheuncertaincorrectionsforresolutionwhichhadtobeapplied quencies usedgaverisetoconsiderableerrorsinsomecasesbecauseofconfusionby at thehigherfrequencieswereincluded.Thisprocedurediscriminatedagainstsourcès were invariablyfoundtohaveasmallangularsizeandhighbrightnesstemperature. the differentfrequenciestoaslowalimitingfluxdensitypossible.Inthisstudyless 2 MHz, whileoverselectedareasofskytheanalysisiscompleteabove15f.u.at38 this workwastostudythestatisticsofsourcespectra,sourcesbeingselectedat the rangeoffrequenciesobserved.Sourceswithextremecurvaturespectrum 262 1 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem * 1fluxunit=KPWin-Hz- . One ofthegreatestdifficultiesindetermination ofradio-sourcespectraisdueto A moresystematicstudyofsourcespectrawasbasedontheobservationsmadewith The presentpaperattemptstoimprovethedataonspectraofstrongerradio The CKLstudy,however,sufferedfromseverallimitations.First,thedatawere Finally, astudyhasbeencarriedoutatCambridgeofthespectraabout1000 KELLERMANN, PAULINY-TOTH,ANDWILLIAMS Vol. 157 19 69ApJ. . . 157 IK which synthesizesapencilbeamof23'inrightascension and18'sec(f)indeclination. made withthemoving-Taperture-synthesisinstrument (CrowtherandClarke1966), were usedinstead: regions themostreliable alternativeobservations,chosenbythefollowing criteria, The presentfluxdensitiesaremoreaccuratethan thosegiveninCKLsincethefull with afanbeamof30'by45°forpartthesky, andwithonlyalimitedsynthesisfor synthesis isnowavailableoverthewholesky,whereas previousobservationsweremade 45' sec(f)(f=zenithangle)indeclination(Williams, Kenderdine,andBaldwin1966). synthesis instrument,whichsynthesizesapencil beamof45'inrightascensionand 5000 2695 the remainder. A summaryofthetelescopesystemsandsourceserrorateachfrequencyisgivenin 3C andParkescatalogueswiththeextensionofspectratoshorterwavelengths latitudes; additionalpapersareinpreparationdealingwithothersourcesfromthe Table 1.Detaileddescriptionswillbefoundelsewhere,asindicatedbelow. No. 1,1969 1400 sources wasunrecognizedatthetimeofCKLstudy. radio andopticalpropertiescanbemade.Inparticular,thewholeclassofquasi-stellar sources, sothatamoremeaningfulstatisticalcomparisonoftheradiospectrawithother optical identifications,redshifts,brightnessdistributions,andpolarizationofdiscrete (Kellermann andPauliny-Toth1969). (Bennett 1962)wherethedataarenearlycompleteforsourcesathighgalactic 750 178 38 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Where possible,fluxdensitiesat178MHz(X=1.7 m)weretakenfromobservations Certain areasofsky,however, werenotsurveyedbythisinstrument,and inthese The observationsat38MHz(X=7.9m)were made withthemoving-Taperture- 1. Wheneverthefluxdensities quotedintherevised3Ccatalogueweredetermined A briefdescriptionoftheequipmentandobservingprocedureusedisgivenbelow. In thepresentpaperdiscussionislimitedtosourcesinrevised3Ccatalogue In additiontotheimprovedspectraldata,moreinformationisnowavailableabout Frequency Characteristics oftheAntennaSystemsUsedatVariousFrequencies According todeclination. (MHz) a) ObservationsattheMullardRadioAstronomyObservatory Cambridge Cambridge Green Bank Green Bank Green Bank Green Bank Observatory Pencil-beam aperture- II. THEOBSERVATIONS Pencil-beam aperture- 4C interferometeraper- 300-foot telescope 300-foot telescope 3C totalpowersystem 140-foot telescope 140-foot telescope RADIO SOURCES ture synthesissystem synthesis system synthesis system ii) 178MHz Instrument i) 38MHz TABLE 1 / ,/ 0?2X4?5 f 45X45 secf 25'X35' secf 23X18 secf ll'XH' lO'XlO' 18:5X18:5 6'X6 Beam Width RMS Noiseand 0 02-0.05 (flux units) Confusion 0 05 0 1 0 2 0 5 0 5 2 0 5-10* 3 19 69ApJ. . . 157 IK 21 o measured intwoorthogonal positionsofthefeedhornandarethusindependent of given atthesetwofrequencies arebasedonthesumofantenna temperatures any linearorcircularpolarization inthesources. sources suspectedofbeingconfusedbyothernearby sources,scansweremadeinright the outputofreceiverfor30secondsineach position.Forlargersources,orfor for whichaccurateradiopositionswereavailable, thefluxdensitiesweredetermined made withthe140-foottelescope,whichhasbeam widthsof11'and6',respectively, ascension anddeclination,anintegratedflux densitywasdetermined.Allvalues by pointingtheantennaalternatelytowardand away fromthesourceandintegrating 5000 MHz(X=6cm)(Pauliny-TothandKellermann 1968),theobservationswere final uncertaintya=(<7„+a?).At750MHz,(70.15f.u.;at1400 lination range50-70°andby4percentinthedeclination70-90°tocorrect at thesefrequencies.Forsourcesknowntobesmall comparedwiththebeamwidthand flux densities. list, inwhichonlytheuncertaintyaduetoreceivernoisewasconsidered.The original NRAOfluxdensitiesat1400MHzhavebeenreducedby2percentinthedec- certainties inthecorrectionforgainoftelescopewithzenithangle,<7*,sothat quoted errorshavebeenincreasedtoallowfortheeffectsofconfusion,o-c,andun- sources, thepolarizationmeasurementsofBolognaetal.(1965,andprivatecommunica- for thiseffect.AsecondcorrectionwasappliedtotheNRAOmeasurementsat1400 list). Theobservationsweremadewiththe300-foottransittelescopeatGreenBank from totalpowerobservations,thesefluxdensitieswerepreferredbecausetheyincludeno radiation withitselectricvectororientedinpositionanglezero.For156ofthestronger MHz toallowforpolarization.Atthisfrequencytheantennafeedwasorientedaccept higher declinationstheNRAOfluxdensitiesweresystematicallyhigh.Theeffectis found thatthespectralindicesquotedinNRAOlistshowedasystematicdependence list ofPauliny-Toth,Wade,andHeeschen(1966)(hereinafterreferredtoastheNRAO however, measurementsmadewiththe4Caperture-synthesisinterferometerwere tion), madewiththe300-foottelescopeat1410MHz,wereusedtocorrectNRAO of suitablecalibrationsourcesintheNRAOlistatdeclinationsgreaterthan52°.The on zenithangle,andwasnotdetectedintheoriginalmeasurementsbecauseoflack showed that,whileagreementwasexcellentforsourcesbelowadeclinationof50°,at on declination.Acomparisonofthedataat1400MHzwiththoseFomalont(1968) and consistedofdriftsthesourcethroughantennapattern,withset apparently duetoanasymmetryinthedependenceofgain300-foottelescope 3C 305 3C 298 3C 341 3C 340 3C 334 3C 330 3C 327.1 3C 327 3C 326 3C 323.1 3C 322 3C 318.1 3C 314.1 3C 310 3C 309.1 3C 305.1 3C 303.1 3C 300.1 3C 300 3C 299 Source 3C 343, 3C 325 3C 321 3C 319 3C 318 3C 303 3C 324 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 220 a 218 a 162 b 119 b 165 b 40 b 36 c 30 c 36 b 31 c 38 c 41 c 67 b 24 d 29 b 58 b 26 c 47 b 43 b 81 b 37 b 49 b 13 e 37 b 29 c 24 c 36 c 28 c 81 b 41 b 49 b 22 d 73 b 13 e 73 b 71 b 86 c 78 b 8 f 38 3 3 3 4 4f 3 3 3 41 56.0 46.9 a 20.6 17.9 a 47.5 a 10.9 a 27.8 23.6 35.3 15.8 49.0 18.9 10.6 22.7 13.5 14.1 a 11.8'b 10.1 a 11.8 a 11.5b 12.1 10.1 13.5 11.3 12.3 12.4 15.7 12.4 11.2 a 10.8 a 12.4 a 11.5 a 10.8 b 15.6 15.3 3 9.6 b 9.1 9.7 8.4 8.2 178 Table 3(Continued) 11.3 a 11.5 a 11.0 a 15.2 a 10.4 a 14.6 a 0.7 d 5.3 a 6.1 a 6.6 a 6.3 a 3.7 b 3.9 a 4.8 a 4.4 a 4.2 a 2.8 b 2.4 b 4.8 a 2.8 b 3.3 b 3.7 b 5.0 a 4.0 a 5.9 a 4.5 a 3.8 a 2.5 b 3.3 b 5.9 a 3.1 b 8.8 a 4.2 a 3.3 b 6.6 a 7.6 a 7.6 a 6.8 a 7.6 a 7.4 a 750 13 <0.1 2.7 a 5.7 a 3.5 a 3.0 a 2.4 a 3.3 b 3.6 a 3.5 a 3.7 a 5.4 a 4.0 a 7.7 a 7.9 a 1.9 b 6.6*a 3.2 b 6.9 a 3.1 b 2.6 a 2.4 a 2.0 a 1.7 b 2.5 a 2.6 a 1.6 b 1.7 b 1.9 b 4.1 a 4.9 a 2.3 a 2.6 a 2.2 a 2.5 a 4.1 a 8.6 a 3.0 b 1.3 b 3.4 a 1400 2.1 a <0.04 0.77 b 0.70 b 0.61 b 2.71 a 2.07 a 3.10 a 5.30 a 0.65 b 0.91 b 2.36 a 1.64 a 1.83 a 1.59 a 5.3 *a 0.85 b 2.11 a 1.13 a 1.55 a 1.92 a 2.68 a 3.76 a 5.21 a 2.03 a 1.33 a 2.23 a 1.35 a 1.57 a 1.39 a 2.10 a 1.35 a 2.07 b 1.84 a 1.29 a 1.25 a 1.08 a 1.24 a 1.32 a 1.46 a 1.26 a 2695 <0.03 0.94 b 0.94 a 0.46 b 0.92 a 0.90 b 0.87 a 0.33 b 0.75 b 0.46 b 1.10 a 1.46 a 0.49 0.91 0.69 0.57 0.61 b 0.92 b 0.65 a 0.75 a 3.76 a 0.69 a 0.83 0.86 0.83 b 0.33 c 0.50 b 1.27 a 1.39 a 0.57 b 2.35 0.46 b 1.28 b 5,5 *a 2.76 1.20 a 1.10 1.22 b 5000 a Notes 26 25 24 25 33 32 32 27 28 31 30 29 19 69ApJ. . . 157 IK 3C 390.3 3C 379.1 3C 371 3C 356 3C 399.1 3C 368 Source 3C 398 3C 394 3C 392 3C 391 3C 390 3C 388 3C 386 3C 382 3C 381 3C 380 3C 357 3C 353 3C 352 3C 351 3C 349 3C 348 3C 346 3C 415.2 3C 409 3C 403.2 3C 403 3C 400.1 3C 411 3C 410 3C 405 3C 403.1 3C 401 3C 400.2 3C 400 3C 399.2 3C 397 3C 396.1 3C 396 3C 402 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 22000 b 1690 a ¿15 211 280 d 120 713 a 100 d 766 d 48 b 50 b 35 c 65 92 35 33 15 e 54 d 30 d 42 c 40 b 96 d 59 d 57 c 81 40 d 50 d 72 48 d 78 d 79 d 38 3 8700. 3 310.0 378.0 236.0 a 351.0 3 3 3 3 3 3 21*0 42.0 62.0 17.0 21.0 68.0 11.3 a 13.8 a 47.5 24.6 23.9 59.4 11.3 13.7 13.3 17.8 20.9 13.5 32.4 23.8 19.9 16.6 10.9 3 54.0 13.5 12.4 16.5 34.6 76.6 10.1 15.1 3.7 b 9.7 c 7.4 8.8 178 Table 3(Continued) 2980. a 643.4 b 231.4 b 84.5 a 22.2 a 83.7 a 44.3 c 10.5 a 40.2 b 28.1 b 16.8 a 25.1 a 16.5 b 15.5 a 23.5 b 12.0 c 71.7 b 9.4 a 5.4 b 2.4 b 4.3 b 2.7 b 3.3 b 5.0 a 4.8 a 5.4 a 8.9 b 2.8 b 2.4 b 4.9 a 9.3 a 3.7 b 4.4 a 2.0 b 5.3 a 4.5 a 7.6 a 2.7 b 8.5 a 7.8 a 750 14 1590. 565.1 b 167.8 b 44.5 54.9 a 14.8*a 20.2 a 11.6 a 13.4 a 13.9 a 35.8 b 10.1 a 73.6 b 16.9 b 28.4 c 3.2 5.6 b 3.8 b 2.6*a 2.0 3.2 3.6 1.7 b 1.1 b 2.7 b 1.4 b 2.6 a 9.0 c 4.6 a 5.6 a 5.9 a 7.0 a 1400 3.2 a 4.7 a 6.7 b 2.3 a 2.6 a 1.1 b 3.0 a 1.8 b 785. a 34.8 a 22.4 a 10, 13.6 19.6 c 39.4 c 0.43 b 0.66 b 0.95 b 2.03 a 2.33 a 3, 1, 1.92*a 1.88 a 6.76 2.79 2, 1.80 a 0.56 b 0.96 b 3.11 4, 6.00 a 3.57 a 2.76 a 1.67 a 6.44 a 1.40 a 1.50 a 1.69 a 1.80 a 2695 30 a 10 a 49 a 32 a 1 *a 371. a 21.5 a 11.89 a 10.07 b 1*0.05 a 14.7 15.2 0.47 b 0.66 b 0.21 b 0.38 b 1.14 a 1.74*a 1.21 a 1.63 b 4.48 a 2.58 a 2.22 a 1.00 a 0.93 b 0.96 b 1.29 a 7.5 *a 0.32 c 0.87 b 0.45 c 0.92 b 1.77 a 1.77 a 3.12 a 2.07 a 3.79 a 1.37 a 5000 Notes 34 36 35 43 38 37 44 42 40 39 46 45 41 47 19 69ApJ. . . 157 IK 3C 470 3C 461 3C 435.1 3C 424 3C 418 3C 468.1 3C 460 3C 458 3C 456 3C 454.2 3C 442 3C 437.1 3C 437 3C 436 3C 435 3C 434 3C 433 3C 432 3C 430 Source 3C 431 3C 428 3C 427.1 3C 469.1 3C 465 3C 459 3C 455 3C 454 3C 452 3C 449 3C 445 3C 441 3C 434.1 3C 454.3 3C 454.1 3C 438 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 37200 b 125 c 118 126 200 187 115 138 37 d 93 58 17 57 53 35 28 43 87 47 32 41 27 c 27 90 41 74 38 11600. s 3 3 3 3 V 4f 41 30.0 54.4 33.7 16.6 37.8 56.2 a 26.6 13.1 12.4 25.6 11.6 44.7 a 14.6 a 12.0 b 11.6 a 24.2 a 14.6 10.1 10.3 14.5 10.6 13.0 24.8 b 20.6 a 16.2 b 17.8 a 32.0 a 11.0b 12.8 11.5 a 12.6 b 4 4.8 b 9.8 8.8 178 b 2.9 a 3.5b a 9.7 a 3880. a 13.4 Table 3(Continued) 19.9 a 11.9 a 12.0 b 12.8*a 18.5 a 13.1 a 5.6 b 6.9 a 4.3 b 4.9 a 5.4 a 3.3 b 2.0 b 2.8 b 6.3 a 6.4 a 4.5 a 7.0 a 6.2 a 4.9 b 2.7 b 3.9 a 4.8 a 3.6 b 3.0 b 3.3 b 5.2 a 4.0 a 7.6 a 8.7 a 750 15 2410. a 11.5 a 11.4 b 10.6*a 10.3 a 3.1 a 3.7 a 5.3*b 3.1 b 2.2 a 1.2 b 2.9 b 4.0 a 3.3 b 2.8 a 3.2 a 2.1 a 1.5 b 7.5 a 5.0 a 2.6 a 3.7 a 5.3 a 1.8 b 7.7 a 2.5 a 2.1 a 3.3 b 2.6 a 6.8 a 1400 1.9 b 1.5 b 2.9 a 2.3 a 1.6 b 1470. a 11.00*a 0.75 b 0.76 b 4.71*a 0.77 b 6.49 a 4.69 a 1.22 a 0.83 b 1.06 a 1.56 a 1.48 a 1.89 a 3.22 a 1.82 a 4.21 a 2.28 a 1.48 a 0.65 b 5.87 a 3.22 a 1.51 a 1.51 a 1.45 a 1.04 a 1.93 a 1.67 a 2.47 a 1.63 a 1.33 a 1.21 a 1.29 a 2695 910. a 18.2 *a 0.96 b 0.65 a 0.86 0.43 b 0.39 3.74 0.31 0.88 b 0.99 a 3.32 a 0.41 b 0.93 b 0.79 a 0.82 b 0.92 a 0.55 b 0.87 a 0.34 b 0.67 a 0.93 b 0.76 a 3>81*a 0.22 d 2.80 a 3.26 b 2.04 a 1.36 a 1.54 a 1.39 b 5000 Notes 48 49 51 50 52 54 53 19 69ApJ. . . 157 IK frequency cutoffbelow750MHz. angular size(Fomalont1968; Bash 1968)withasharpcutoffnear750MHzandhigh-frequency spec- 1400 MHz,1.3bat2695and0.48a5000MHz. spectrum, suggestingacutoffinbothcomponents.Thisisalso suggestedbythe81.5-MHzfluxdensities bined fluxdensityisconsiderablylessthantheobtained byextrapolationfromthehigh-frequency all frequenciesbetween178and5000MHz.Thetwosources arenotresolvedat38MHz,butthecom- below 750MHz.At2695MHz70percentofthefluxcomesfromacomponentlessthan3"inangular ured ratiostoCasA(Heeschen1961). diameter (Bash1968)whichmaybecomeopticallythickat lowfrequencies. have beenreported(Moffet1961;Lequeux1962).Fluxdensitiesat750and1400MHzderivedfrommeas- ing atleastthreeopticallythickcomponents(KellermannandPauliny-Toth1969). The spectrumiscomplex,consistingofcomponentAwithanormalandÈcontain- component (Fomalont1968). (Branson 1967).Thesesourcesmaybesimilarto3C343and 343.1. 178 MHzin3C287. and Kenderdine1967),resultinginashouldertheradiospectrum. all at38MHz,butasthebackgroundtemperatureisnotaccuratelyknown,noelectroncan Toth 1969). estimated tobe14000°±1500°K. at 38MHzwherethebackgroundtemperatureis14000°K,sothatelectronin3C139.1 Wade, andHeeschen(1966)Fomalont(1968).Fluxdensitiesabove750MHzrefertothesmall arc awayandformspartof3C177. be derived.Fluxdensitiesat2695and5000MHzmeasuredbyAltenhoff(privatecommunication). gest non-thermalsource,suchasasupernovaremnant. 3C 461. least 10percentofthefluxcomesfromacomponentlessthanfewsecondsinangulardiameter(Bash density ofNRAO339aloneis3.0aat1400MHz,1.442695and0.655000MHz. interpolated fromHogg’smeasurementsat1400and3000MHz. 1965). shorter wavelengths. due toconfusionby4C-01.04.(NRAO49,P0053-01). 1968) whichmaybecomeopticallythickatlowfrequencies. 1961). Fluxdensityat5000MHzdeterminedfrommeasuredratiotoCasA(Baars,Mezger,andWendker (Sastry, Pauliny-Toth,andKellermann1967;HobbsHaddock1967)lowgalacticlatitudesug- © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 30. 3C326.1:Verymarkedshoulderbetween178and750MHz suggestsamajorcomponentofsmall 29. 3C326:IncludesNRAO485and487atallfrequencies. FluxofNRAO487aloneis1.9ftat 26. 3C315:Possiblyashoulderbetween178and750MHz. 25. 3C306.1:Datamaybeconfused. 28. 3C321:Shoulderbetween178and750MHzsuggests existenceofacomponentwithlow- 27. 3C318.1:Steepestspectrumknown.Sourceisnotdetected at1400,2695,and5000MHz. 24. 3C303.1and305.1:Thesetwosources,15'ofarcapart, havenearlyidenticalfluxdensitiesat 22. 3C287:Sasincludesfluxfrom4C25.44,sothatthereisprobablyalow-frequencycutoffbelow 21. 3C286:Flatspectrumbelow1400MHzprobablyduetopartialself-absorption. 23. 3C293:Shoulderbetween178and750MHzindicatescomponentwithalow-frequencycutoff 20. 3C274:Over-allspectrumisremarkablystraight,althoughcomponentswithdifferentspectra 9. 3C139.1:Thermalspectrumbecomingopticallythickbelow500MHz.Nosourcedetectedatall 19. 3C273:Onlyalowerlimitisgiventothefluxdensityat38MHz,whichconfusedby274. 18. 3C236:DataareconfusedbyNRAO346plusanextendedsourceofemission.SeePauliny-Toth, 16. 3C230:Twocomponents,NRAO339(4C00.32,P0949+00)and340(P0950+00).Flux 3. 3C29:Fluxdensitiesof4C—01.05(NRAO50,P0055—01)usedatallfrequencies.¿Wuncertain 17. 3C231:Flatspectrumbelow1400MHzmaybeduetopartialself-absorption.At2695at 8. 3C135:Smseemshigh;possiblyconfusedby01.13. 6. 3C84:Verycomplexandvariablespectrum(RyleWindram1968;KellermannPauliny- 4. 3C40:Scatterinfluxdensitiesprobablyduetolargeerrorscorrectionforangularsizeatthe 15. 3C225:Doublesource.Onecomponenthasalow-frequencycutoffnear50MHz(Macdonald 11. 3C147.1:Thermalspectrumbecomingopticallythickbelow1000MHz.Nosourcedetectedat 10. 3C144:TauA.Fluxdensityat1400MHzdeterminedfrommeasuredratiotoCasA(Heeschen 5. 3C58:Spectrumunusuallyflat,butnotstraight.Highpolarizationatcentimeterwavelengths 14. 3C177:DatarefertoNRAO261(4C15.19,P0721+15).4C16.21(P0721+16)isabout50'of 12. 3C153.1:Thermalspectrumwhichisopticallythinevenat38MHz. 7. 3C129:Includes129.1atallfrequencies. 2. 3C14.1:Consistsoftwocomponents.Fluxdensities4C58.02(NRAO28)usedatallfrequencies. 13. 3C157:IC443.Fluxdensitiesat750and1400MHzbasedonHogg^(1964).density2695 1. 3C6.1:5ssquotedbyWilliams,Kenderdine,andBaldwin(1966)unreliableduetoconfusion NOTES TOTABLEß 16 19 69ApJ. . . 157 IK region. Uncertainidentifications arenotedwithaquestionmark. marized inTable4asfollows: values ofa(l78-38)ora(5000-2695)insteada(750-38) anda(5000-750),althoughthe galaxy, QSSforquasi-stellar sources,SNRforsupernovaremnant,andH nforH statistical discussionin§V6isbasedentirelyonthe latterindices.Theresultsaresum- given inTable2. with HB21. perature. Nofluxdensitymeasuredat2695or5000MHz. spectrum. ThesourceW49(Westerhout1959)includesboththethermal(NRAO598)andnon-thermal from ratiostoCasAmeasuredbyHeeschen(1961);andat5000MHz,ratio components (NRAO599).Fluxdensityat5000MHzmeasuredbyAltenhoff(privatecommunication). gen. Fluxdensitiesat2695and5000MHzmeasuredbyAltenhoff(privatecommunication). spite oftheobviouscurvaturespectrum.For thesesources,therefore,wequote difference betweenthehigh-andlow-frequency indices maynotappearsignificantin of sources,givesagoodfit;moreover,theresults are wellsuitedforstatisticalanalysis. Parker (1968).Fluxdensitiesatotherfrequenciesobtainedfrominterpolationofabsolutemeasurements quencies, theformalerrorscomputedforthesesources arelarge,andasaresultthe constant indexdoesnotdescribethespectrumeven overtheselimitedrangesoffre- However, forsourceswithmarkedcurvaturethe resultsmaybemisleading.Sincea data fromthestraightline.Thisprocedureissimple andobjectiveand,forthemajority Pauliny-Toth 1969). Baars, Mezger,andWendker(1965). remnant. component thatisopticallythickat5000MHz. tainty. Thestandarderrorinthespectralindexwas derivedfromthedeviationsof 669, P2148+13).Fluxdensitiesgivenaresumofbothcomponents.density4C14.80is9.6bat b at1400MHz,and0.482695MHz. Pauliny-Toth 1968). radiation. away, andalsohasacomplexspectrum. diameters andareprobablyopticallythickatlowfrequencies(Moffet1965;Williams1966). sities atallfrequencies,includingasharpcutoffbelow178MHz.Bothhaveextremelysmallangular 1.8 bat1400MHz,0.97a2695and0.75000MHz;NRAO664is2.07501.3 Heeschen 1966)whichhasanindexofabout—1.3. 178 MHz,3.1bat7502.11420and1.3a2695MHz. tral indexnear—0.9.Inaddition,thereisamoreextendedcomponent(Pauliny-Toth,Wade,and © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 49. 3C428:Largeuncertaintiesinfluxdensitiesduetogalacticradiation. 42. 3C397:Non-thermalspectrum.Low-frequencycutoffmaybeduetoabsorptionbygalactichydro- 54. 3C461:CasA.Allfluxdensitiesforepoch1964.4.Fluxdensityat38MHzfrommeasurementsby 53. 3C454.3:Complexspectrumwithseveralopticallythickvariablecomponents(Kellermannand 50. 3C434.1:Largeuncertaintiesinfluxdensitiesduetogalacticradiation. 48. 3C418:Spectralcurvaturesuggestscomponentopticallythickbelow5000MHz.Someconfusion 47. 3C405:CygA.Fluxdensitiesat38and178MHztakenfromCKL;750,2695,1400MHz, 46. 3C403.2:Fluxdensityat2695measuredbyAltenhoff(privatecommunication). 44. 3C399.1:Largeuncertaintiesinfluxdensitiesduetogalacticradiation. 43. 3C398:Thespectrumisflat,althoughnon-thermal.NRAO598only15'awayandhasathermal 41. 3C396.1:Largeuncertaintiesinallfluxdensities. 40. 3C396:Flatnon-thermalspectruminasourceatlowgalacticlatitudesuggestssupernova 34. 3C371:Complexvariablespectrumwithseveralopticallythickcomponents(Kellermannand 36. 3C382:Possiblyashoulderbetween178and750MHz. 51. 3C435.1:IncludesNRAO663and664.Fluxdensityofis3.66at750MHz, 45. 3C400:ComplexHnregion.Lowapparentfluxdensityat38MHzduetohighbackgroundtem- 39. 3C394:Appearstohavealow-frequencycutoffbelow178MHz,butregionisconfusedbygalactic 37. 3C390.3:Possiblyashoulderbetween178and750MHz. 38. 3C392:W44(Westerhout1959).Fluxdensitiesat2695and5000MHznotwelldetermined. 32. 3C343and343.1:Thesetwosourcesare30'ofarcaparthavenearlyidenticalfluxden- 31. 3C327:Possiblyashoulderbetween178and750MHz. 35. 3C380:Spectralcurvatureandpossibleslowvariationinfluxdensityathighfrequencysuggesta 52. 3C437.1:Consistsoftwocomponents,4C14.80(NRAO668,P2148+14)and13.82 Column (2):Opticalidentification whereavailable.Thesymbolsused are: Gfor Column (1):Thesourcenumber intherevised3Ccatalogue. 33. 3C345:Complexspectrumwithseveralopticallythickvariablecomponents.NRAO512is30' RADIO SOURCES17 19 69ApJ. . . 157 IK 3C 58 3C 48 3C 47 3C 40 3C 61.1 3C 55 3C 54 3C 52 3C 46 3C 44 3C 43 3C 36 3C 35 3C 34 3C 33.2 3C 33.1 3C 49 3C 41 3C 29 3C 22 3C 18 3C 17 3C 14 3C 13 3C 63 3C 42 3C 33 3C 20 3C 19 3C 16 3C 15 3C 10 3C 28 3C 27 3C 14 3C 11.1 3C 31 3C 3C 3C Source © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 9 6.1 2 I den. QSS QSS? QSS QSS? QSS QSS QSS SNR? SNR G G G G G? G? G G [-0.07 (-0.62 (-0.88 (-0.82 (-0.80 (+0.11 -0.83 -0.94 -0.90 -0.92 -0.55 -0.75 -1.05 -0.69 -1.01 -0.75 -0.62 -0.68 -0.63 -0.85 -0.63 -0.77 -0.71 -0.84 -0.58 -0.97 -1.01 -0.73 -0.69 -0.89 -0.67 -0.59 -0.77 -0.61 -0.67 -0.93 -0.78 -0.62 -0.99 -0.67 Spectral Indices ’38 750 Table 4 0.04 0.02 0.06 0.03) 0.05 0.10 0.04 0.01 0.01 0.02 0.01 0.08 0.01 0.08) 0.01 0.02 0.02 0.08 0.03 0.05) 0.02 0.11 0.09 0.02 0.06 0.10) 0.01 0.01 0.08 0.03 0.07] 0.01 0.04 0.07 0.16 0.03 0.17 0.09 0.03) 0.01 18 (-1.01 -0.10 -0.92 -0.95 -0.93 -0.71 -0.81 -0.80 -0.94 -0.95 -0.68 -0.89 -0.78 -0.84 -0.71 -0.86 -0.74 -0.68 -0.65 -1.22 ■0.82 •0.75 •0.71 •0.66 ■0.94 ■0.74 •1.06 ■0.91 •1.08 •0.99 ■0.5 •1.02 •0.89 0.03 •0.74 ±0.01 ■1.0 ■0.78 ■0.98 ■0.86 ■0.94 •0.89 '750 ,5000 0.03 0.02 0.03 0.04 0.03 0.03 0.03 0.05 0.03 0.05 0.01) 0.03 0.03 0.02 0.01 0.03 0.06 0.04 0.02 0.03 0.04 0.02 0.04 0.01 0.02 0.01 0.04 0.01 0.04 0.05 0.01 0.06 0.03 0.02 0.03 0.11 0.04 0.03 Class 19 69ApJ. . . 157 IK 3C 103 3C 111 3C 114 3C 109 3C 107 3C 105 3C 99 3C 98 3C 93.1 3C 91 3C 84 3C 76.1 3C 137 3C 136.1 3C 124 3C 119 3C 93 3C 89 3C 88 3C 86 3C 79 3C 78 3C 69 3C 67 3C 135 3C 134 3C 133 3C 131 3C 125 3C 123 3C 83.1 3C 71 3C 68.2 3C 68.1 3C 132 3C 130 3C 129 3C 75 3C 66 3C 65 Source © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Iden, QSS QSS G G G G G G G G G G G? G G Table 4(Continued) (-0.55 -0.70 -1.11 -0.80 -0.76 ■0.81 ■0.83 ■0.82 •0.96 ■0.65 ■0.67 •0.78 ■0.86 ■0.89 ■0.9 ■0.96 ■0.69 ■0.2 ■0.9 ■0.75 •0.76 ■0.9 ■0.62 ■0.78 ■0.92 ■0.74 ■0.63 ■0.76 ■0.67 ■1.0 ■0.58 ■0.65 •0.93 •0.72 ■0.7 ■0.51 ■0.70 •0.75 ■0.53 ■0.85 '38 750 19 0.01 0.01 0.07 0.01 0.11 0.06 0.08 0.07 0.03 0.02 0.05) 0.06 0.12 0.07 0.07 0.01 0.01 0.02 0.03 0.05 0.20 0.06 0.10 0.04 0.04 0.04 0.24 0.02 0.02 0.05 0.01 0.01 0.07 0.05 0.03 0.02 0.04 0.03 0.02 0.13 [+1.02 -0.78 -1.01 -0.83 -0.72 -0.69 -0.60 -0.68 -0.98 -0.54 -0.62 -0.71 -1.35 -0.86 -0.62 -0.84 -1.02 -0.85 -0.78 -0.98 ■0.96 •0.67 •0.80 ■1.7 ■0.73 ■0.86 ■0.91 ■0.83 •0.94 ■1.02 ■0.95 ■0.79 •0.65 ■0.92 ■0.68 •0.75 ■1.02 ■0.72 ■0.95 ■0.6 a 750 5000 0.09 0.05 0.01 0.05 0.05 0.07 0.03 0.02 0.03 0.04 0.01 0.06 0.01 0.04 0.12] 0.02 0.02 0.01 0.02 0.02 0.01 0.03 0.04 0.05 0.02 0.01 0.02 0.03 0.03 0.04 0.05 0.06 0.03 0.04 0.04 0.06 0.02 0.05 0.01 0.06 Class C- C- C- C- Cpx C- S C- Cpx S S S S S C- C- C- C- S S C- C- C+ s s C- c- S S s 19 69ApJ. . . 157 IK 3C 153 3C 204 3C 198 3C 197.1 3C 194 3C 191 3C 196.1 3C 196 3C 192 3C 190 3C 187 3C 181 3C 180 3C 177 3C 169.1 3C 158 3C 157 3C 147 3C 144 3C 141 3C 139.2 3C 138 3C 175.1 3C 175 3C 173.1 3C 172 3C 165 3C 154 3C 152 3C 147.1 3C 142.1 3C 139-1 3C 200 3C 186 3C 184.1 3C 184 3C 171 3C 166 3C 153.1 3C 173 Source © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Iden. HIT HIT QSS QSS QSS QSS QSS QSS QSS QSS QSS HIT SNR SNR G G G G G G G G G G Table 4(Continued) (+0.84 (+0.38 [+0.77 [+0.35 +0.24 -0.77 -0.62 -0.79 -0.90 -0.85 -0.73 -0.25 -0.30 -0.99 -0.98 ■1.0 ■0.85 ■0.79 ■0.7 •1.09 ■0.68 ■0.75 ■0.7 ■0.92 •0.80 ■0.97 ■1.02 ■0.6 ■0.74 ■0.86 ■0.81 ■0.9 ■0.8 ■0.96 ■0.81 •0.67 ■0.75 ■0.74 ■0.89 ■0.96 a 750 38 20 0.10) 0.10 0.01 0.04 0.02 0.09 0.08) 0.17] 0.01 0.04 0.02 0.02 0.25] 0.03 0.07 0.05 0.13 0.09 0.02 0.10 0.12 0.05 0.03 0.04 0.10 0.01 0.04 0.04 0.12 0.14 0.01 0.09 0.02 0.04 0.08 0.08 0.01 0.07 0.03 0.04 (-0.03 (-0.25 (+0.06 (-0.08 -0.78 -0.56 -0.82 -1.31 -0.74 -0.92 -1.05 -0.97 -0.71 -0.26 -0.98 ■1.04 ■0.89 ■1.05 •0.67 ■1.05 ■0.8 ■0.89 ■0.7 ■1.0 ■0.86 ■0.81 ■0.89 •0.90 ■1.02 ■0.92 •0.96 •0.89 ■0.84 ■0.8 ■0.67 •1.00 ■1.08 ■0.76 •1.00 ■0.89 '750 ,5000 0.16) 0.05 0.02 0.04 0.06 0.08 0.05 0.08) 0.07) 0.05) 0.03 0.02 0.02 0.14 0.04 0.02 0.07 0.07 0.03 0.01 0.02 0.02 0.03 0.04 0.01 0.05 0.02 0.03 0.11 0.09 0.05 0.05 0.05 0.05 0.02 0.05 0.06 0.09 0.01 0.02 Class T T T C- C- S S C- S S C- C- S C- C+ S c- c- s s 19 69ApJ. . . 157 IK 3C 231 3C 228 3C 223.1 3C 239 3C 257 3C 238 3C 236 3C 234 3C 230 3C 227 3C 226 3C 225 3C 223 3C 220.3 3C 220.1 3C 219 3C 217 3C 216 3C 215 3C 256 3C 255 3C 254 3C 252 3C 250 3C 249.1 3C 249 3C 247 3C 245 3C 244.1 3C 241 3C 237 3C 220.2 3C 210 3C 208 3C 207 3C 205 3C 222 3C 213.1 3C 208.1 3C 212 Source © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem I den QSS QSS QSS QSS QSS QSS QSS QSS QSS G G? G G G G G G G Table 4(Continued) (-0.94 -0.25 -0.82 -0.72 -0.80 -0.97 -0.76 -0.49 -0.83 -0.80 -0.78 -0.82 -0.58 -0.90 -0.82 -1.00 -0.81 -0.70 -0.62 -0.80 -0.71 -0.80 -0.62 •1.01 ■0.68 •0.62 ■0.82 ■0.74 ■0.75 ■0.72 ■0.94 -0.56 ■0.79 ■0.84 ■0.87 ■0.76 •0.85 ■1.08 ■0.8 0.07 ■0.84 ±0.01 ’38 750 0.02 0.01 0.07 0.03 0.08 0.08) 0.07 0.06 0.05* 0.03 0.14 0.23 0.02 0.06 0.10 0.02 0.18 0.01 0.05 21 0.01 0.12 0.06 0.06 0.04 0.03 0.11 0.03 0.01 0.12 0.01 0.01 0.13 0.03 0.03 0.01 0.21 0.04 0.01 (-0.92 -0.83 -0.70 -0.95 -0.54 ■1.50 ■1.5 ■0.85 •1.10 •0.93 ■1.09 ■0.65 ■1.0 •0.68 ■0.84 •0.96 ■0.79 ■1.5 ■0.52 ■0.94 ■0.82 ■1.0 •0.95 ■0.6 ■0.73 ■0.92 ■1.06 ■1.46 •1.01 ■1.2 ■1.6 ■0.79 ■1.04 ■0.8 •0.67 •0.94 •1.14 ■1.5 ■1. ■0.84 a 750 5000 0.06 0.03 0.03 0.05 0.06 0.15 0.02 0.01 0.01 0.03 0.07 0.02 0.06 0.02 0.06 0.10 0.06 0.03 0.07 0.02 0.02 0.05 0.04 0.02 0.02 0.01 0.03 0.06 0.06 0.04 0.01 0.05 0.04 0.03 0.03) 0.03 0.08 0.05 0.05 0.05 Class C- C- C+ C- C- C- C+ S C- C- C- S C- C- S 19 69ApJ. . . 157 IK 3G 297 3C 295 3C 294 3C 293 3C 296 3C 293.1 3C 288.1 3C 266 3C 289 3C 288 3C 287.1 3C 286 3C 285 3C 284 3C 280 3C 277.3 3C 277.2 3C 277.1 3C 272 3C 270.1 3C 268.3 3C 268.1 3C 274 3C 273 3C 272.1 3C 268.2 3C 265 3C 264 3C 263.1 3C 263 3C 258 3C 287 3C 280.1 3C 277 3C 275.1 3C 274.1 3C 270 3C 268.4 3C 267 3C 275 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Source Iden, QSS QSS QSS QSS QSS QSS QSS QSS QSS QSS G G G G? G G G G G G G G Table 4(Continued) (-1.27 ± (-0.46 (-0.25 [-0.08 -0.61 -0.99 -1.10 -0.99 -0.54 -0.63 -0.85 -0.92 -0.88 -0.83 -0.74 -0.91 -0.56 -0.81 -0.87 -0.91 -0.76' -0.76 -0.76 -0.71 -0.78 -0.74 -0.36 -0.19 -0.72 -0.71 -0.96 -0.59 -0.89 -0.61 -0.79 -0.57 -0.67 -0.53 -0.84 -0.83 750 38 22 0.01 0.02 0.01 0.05) 0.05 0.06 0.04 0.08 0.02 0.06] 0.01 0.03 0.02 0.13 0.01 0.14) 0.05 0.05 0.10 0.08 0.07 0.15 0.02 0.03 0.01 0.05) 0.01 0.21 0.08 0.07 0.01 0.04 0.16 0.05 0.08 0.02 0.10 0.01 0.13 0.01 (-1.17 [+0.12 -0.70 -0.90 -1.02 -0.89 -0.57 -0.95 -0.60 -1.14 -0.69 -0.99 -0.95 -0.51 -0.58 -1.09 -0.86 -0.65 -0.92 -0.64 -0.58 -1.00 -0.47 -0.75 -0.82 -1.00 -0.88 -0.92 -1.03 -0.80 •0.85 ■0.97 •0.69 ■0.94 ■1.7 •1.10 ■0.81 ■1.03 •0.82 0.01 •0.75 ±0.11 a 750 5000 0.01 0.04 0.06 0.02 0.08 0.06 0.02 0.03 0.03 0.07 0.06 0.04 0.04 0.02 0.11 0.03 0.07 0.04 0.07 0.02) 0.01 0.04 0.03 0.07 0.02 0.06 0.03 0.11 0.03 0.12] 0.03 0.02 0.15 0.07 0.02 0.04 0.06 0.01 Class C+ C- c- C- C- C- C- C- S s S S C- Cpx S S C+ Cpx C- C- C- C- C- C- S C- C- C- S C- C- C+ S S S S C- S S S 19 69ApJ. . . 157 IK 3C 305.1 3C 345 3C 343.1 3C 343 3C 303.1 3C 303 3C 300.1 3C 300 3C 299 3C 330 3C 323.1 3C 323 3C 320 3C 318.1 3C 314.1 3C 313 3C 310 3C 306.1 3C 305 3C 298 3C 340 3C 336 3C 332 3C 327.1 3C 327 3C 326.1 3C 326 3C 325 3C 324 3C 322 3C 321 3C 318 3C 315 3C 309.1 3C 341 3C 338 3C 337 3C 334 3C 319 3C 317 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Source Iden, QSS QSS QSS QSS QSS QSS G G G G G G G? G G G G G G? Table 4(Continued) [-0.03 [-0.03 (-0.28 (-0.34 [-0.31 -0.78 -0.61 -0.92 -0.84 -0.89 -0.45 -0.82 -0.79 -0.74 -0.68 -0.62 -0.84 -0.73 -0.92 -0.79 -0.81 -0.43 -0.73 -0.63 -0.82 -0.30 -0.63 -0.68 -0.74 -0.59 -0.73 -0.97 -0.80 -0.73 -1.09 ■0.73 ■0.74 ■0.81 ■1.60 •0.69 a 750 38 23 0.01 0.02 0.04 0.07] 0.01 0.06 0.06 0.-20] 0.03 0.01 0.07 0.04 0.01 0.02 0.20] 0.05) 0.13 0.10 0.01 0.01 0.03 0.09 0.02 0.04 0.08 0.05) 0.01 0.12 0.29 0.04 0.04 0.01 0.04 0.01 0.24 0.04 0.05 0.04 0.14 0.01 <-1.9 (-0.95 [+0.08 -1.08 -0.83 -0.96 -1.06 -1.02 -0.92 -0.99 -0.84 -1.03 -1.05 -0.79 -0.81 -1.01 -0.84 -1.15 -1.00 -0.88 -0.93 -0.97 -0.83 -1.54 -0.91 ■1.36 ■0.86 •1.09 •0.81 ■1.29 ■0.57 ■0.8 •0.92 ■0.8 ■1.07 ■0.74 ■0.93 ■0.91 ■0.8 0.01 ■1.0 ±0.03 750 5000 0.02 0.06 0.03 0.10 0.05 0.03 0.10 0.06 0.01 0.09 0.09 0.04 0.20 0.03 0.12] 0.01 0.04 0.06 0.01 0.01 0.03 0.10 0.04) 0.09 0.06 0.01 0.02 0.02 0.03 0.06 0.02 0.05 0.08 0.02 0.03 0.05 0.05 Class C- Cpx C- C- C- C- C- C- c- s C- C- C- Cpx C- C- C- S ? c- 19 69ApJ. . . 157 IK 3C 371 3C 351 3C 349 3C 346 3C 357 3C 356 3C 352 3C 348 3C 391 3C 390 3C 382 3C 380 3C 379.1 3C 368 3C 353 3C 394 3C 390.3 3C 388 3C 386 3C 381 3C 400.1 3C 400 3C 399.2 3C 399.1 3C 398 3C 397 3C 396.1 3C 396 3C 392 3C 403.2 3C 403.1 3C 401 3C 400.2 3C 409 3C 405 3C 403 3C 402 3C 415.2 3C 411 3C 410 Source © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Iden, QSS QSS HII SNR G G G G G G G G G G G G? Table 4(Continued) (-0.68 (-0.23 (+0.36 (40.52 (-0.25 (-0.56 (-1.02 (40.20 (-0.83 (-0.44 (-0.78 [+0.28 -0.76 -1.00 -0.53 -1.15 -0.61 -0.71 -0.84 -0.70 -0.43 -0.97 -0.65 -0.65 -0.74 -0.76 -0.59 -0.68 -0.36 -0.70 -0.74 -0.89 -0.49 -1.01 -0.52 -0.79 -0.57 -0.78 -0.66 -0.64 a 750 38 0.05 0.05 0.16 0.11 0.02 0.01 0.01 0.08 0.10 0.01 0.01 0.04 0.14 0.04 0.01 0.10 0.20] 0.08) 0.03 0.07 0.13 0.13) 0.18 0.10) 0.04 0.10) 0.08 0.05) 0.05) 0.08) 0.10 0.05) 0.03 0.10) 0.01 0.02 0.04 0.08) 0.10) 0.03 24 [-0.17 (-0.78 0.02) (-0.34 (-0.46 (-0.25 (-0.52 (-0.59 (-0.39 (-0.16 -0.65 -1.30 -0.77 -1.05 -0.77 -1.03 -0.72 -0.74 -0.57 -0.99 -0.74 -0.74 -0.76 -0.74 -0.88 -0.51 -0.57 -0.78 -0.77 -0.88 -0.92 -0.80 -0.87 -0.90 -1.00 -0.94 -0.76 -1.11 -1.09 -0.74 a 750 5000 0.02 0.01 0.01 0.02 0.03 0.03 0.06 0.07 0.05 0.06 0.12] 0.04 0.03 0.03 0.01 0.25) 0.03 0.01 0.08) 0.02 0.03) 0.06 0.03 0.03 0.09 0.05 0.13) 0.05 0.02 0.16) 0.03 0.10 0.16) 0.15) 0.02 0.02 0.04 0.02 Class c- S C- S S Cpx S S S s c+ c- S Cpx c- 19 69ApJ. . . 157 IK * No38or750MHzfluxdensity.Index quotedisbetween 3C 454.1 3C 452 3C 470 3C 469.1 3C 468.1 3C 465 3C 461 3C 460 3C 458 3C 454.3 3C 454.2 3C 438 3C 437.1 3C 437 3C 459 3C 456 3C 455 3C 454 3C 449 3C 445 3C 442 3C 441 3C 436 3C 435.1 3C 435 3C 434.1 3C 434 3C 432 3C 431 3C 430 3C 427.1 3C 424 3C 433 3C 428 3C 418 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 178 MHzand1400MHz. Source Iden QSS SNR QSS QSS G G G G G? G G G G G G G Table 4(Continued) (-0.93 (-0.61 (-0.82 (-0.72 (-1.01 (-0.78 (-0.55 (-0.43 ±0.05) -0.74 -0.76 -0.76 -0.69 -0.70 -0.09 -0.81 -0.76 -0.85 -0.88 -0.78 -0.74 -0.92 -0.72 -0.84 -0.71 -0.85 0.01 ■0.59 ■0.74 ■0.85 ■0.53 ■0.86 •0.56 ■0.63 •0.72 ■0.95 ■0.94 a 750 38 0.04 0.03 0.06 0.07 0.10) 0.03 0.05) 0.20 0.02 0.06 0.06 0.02 0.01 0.02 0.04 0.03 0.05) 0.01 0.14) 0.11 0.01 0.02 0.09 0.08 0.09 0.08) 0.10) 0.02 0.13 0.10) 0.03 0.01 0.03 25 (-0.99 (-0.65 (-0.98 (-0.09 [+0.86 -0.90 -0.91 -0.76 -0.90 -0.63 -0.92 -0.85 -0.88 -1.07 -1.15 -0.77 -0.81 -0.94 -0.90 -0.83 -1.24 -0.77 -1.09 -0.78 -1.13 -0.97 -1.04 -1.29 -0.84 -1.07 ■0.68 ■1.3 ■1.07 ■0.98 ■0.27 750 5000 0.23) 0.02 0.07) 0.05 0.04 0.03 0.03 0.05 0.13] 0.10 0.02 0.01 0.04 0.15) 0.02 0.14) 0.01 0.06 0.03 0.03 0.15 0.03 0.06 0.07 0.06 0.01 0.06 0.06 0.01 0.01 0.01 0.02 0.02 0.04 0.02 Class C- C- C- C- C+ C- C- C- C- C- S S C- C- S C- C- Cpx C- S S S S S ? ? C- S S C- 19 69ApJ. . . 157 IK mann andPauliny-Tothunpublished).Accuratefluxdensitieswerealsoavailableat fined inthenextsection.Inclassifyingspectrawehaveoccasionallyusedflux 3C 454.3),thevalueofa(5000-2695)isgiveninsquarebrackets.Whereoneortwo the spectrumshowsasharpcut-offatfrequenciesbelow178MHz(e.g.,3C48,138, densities at10MHz(BridleandPurton1968)40515GHz(Keller- and 3C147),thevalueofa(138-38)isgiveninsquarebrackets.Iffluxdensityat38 26 MHz; ifthespectrumshowsalargedeparturefrompowerlaw(e.g.,3C84,3C273,and MHz isunavailable,thelow-frequencyspectralindexhasbeendeterminedbetween line (seeFigs.1and2);thespectrumofsuchasourceisthereforedescribedas“straight.” 81.5 MHzforsourcesatdeclinationsgreaterthan+70°(Branson1967). the fluxdensitiesinthisrangearenotavailable,indexisgivenroundbrackets. a simplepowerlaw,sothatiflog{Sf}isplottedagainst(p),thedatalieonstraight discussed below. for about40percentofsourcestheradiationshouldfollowasimplepowerlawsoac- With theincreasedaccuracyofflux-densitymeasurementsoverafrequencyrange 178 and750MHzonly,thisisindicatedbyquotingtheindexinroundbrackets. for theproductionofrelativisticparticles.Itisespeciallysurprisingthatsomesources, bution inelectronenergywhichmustbeaccountedforanyproposedmechanism power lawissmallerthantheCKLstudyhadsuggested.Itremarkable,however,that although theyareknowntocontainseveralcomponentswithapparentlydifferent such asVirA(3C274),haveanover-allspectrumwhichfollowsasimplepowerlaw, curately oversuchalargefrequencyrange.Thisimplieswell-definedpower-lawdistri- spectra (Moffet1961;Lequeux1962). frequencies maydisguiseanyfurthercurvature.The frequencyofmaximumcurvature whole frequencyrange;instead,thereappearsto be awell-definedpower-lawspectrum tween 38and5000MHzthefluxdensityat1000MHz. selection ofthesesourcesislistedinTable5,givingthebest-fittingspectralindexbe- often appearstoliebetween750and1400MHz, thoughthismaypartlydependon compatible withanotherflatterpower-lawspectrum, althoughthelargererrorsatlow Fig. 3).Inmostcasesthisdoesnotappeartobethe resultofagradualcurvatureoverthe 125:1, theproportionofsourceswhichdonotshowasignificantdeparturefromsimple spectra ofsuchsourcesare describedashavingpositivecurvature(seeFig. 5).Insome synchrotron self-absorption(Slish1963;Williams 1963). above thefrequencyofmaximumcurvature,andoften thedatabelowthisfrequencyare 3C 48,147,and298,Fig.4).Suchspectra arealwaysassociatedwithsourcesof 750)|, andthespectraofsuchsourcesaredescribedashavingnegativecurvature(see extremely highbrightnesstemperature,anditis probablethatthecutoffisdueto the selectionoffrequenciesusedinpresentstudy. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Column (3):Thespectralindex,a(750-38),determinedbetween38and750MHz;if Column (5):Aqualitativeclassificationdescribingtheformofspectrumasde- Column (4):Thespectralindex,a(5000-750),determinedbetween750and5000 The variousclassesofradiospectraareillustratedinFigures2,3,4,and5, For somesources*thespectrumoverwholefrequencyrangecanbedescribedby As sourceswithstraightspectraareespeciallyusefulforcalibrationpurposes,a In alargeproportionofsources|a(750-38)issignificantlysmallerthana(5000- In afewsources,|a(750-38)| issignificantlylargerthan|a(5000-750) |, andthe In afewcasesthereisverysharpcutoffinthe spectrumatlowfrequencies(e.g., KELLERMANN, PAULINY-TOTH,ANDWILLIAMS a) ClassificationofRadioSpectra iii) ClassC+{ConcaveSpectra) ii) ClassC—{ConvexSpectra) i) ClassS 0^1 0^1 Fig. 5.—Spectra ofsomesourceswhichhave positivecurvature.Vertical scale isarbitrary. Fig. 4.—Spectraofsomesources whichshowasharplow-frequencycutoff.Verticalscale isarbitrary. FLUX DENSITY « « FLUX DENSITY © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem i. 2.—Spectraofsomesourceswithconstantspectralindices.Verticalscaleisarbitrary. . 3.—Spectraofsomesourceswithnegativecurvature.Verticalscaleisarbitrary. FREQUENCY (MHz) Fig 4 Fig. 23 Fig. 5 19 69ApJ. . . 157 IK so thatatfrequenciesbelowthecutofffrequency only theothercomponentisobserved. about equalintensitiesandspectralindices athighfrequencies,butinonecom- with differentspectra.Forexample,somesourceshavea“shoulder”inthespectrum component ofsmallangulardiameterwithalow-frequency cutoffbelowabout200 observations madewiththeCambridge1-miletelescope whichshowsineachcasea ponent thereisalowfrequencycutoffwithinthe rangeofthepresentanalysis, frequencies, particularly below 38MHz,wouldprobablydisclosefurther examplesof MHz (MacdonaldandKenderdine1967).More completespectraldataatthelower In atleasttwosuchsources,3C225and267, thisinterpretationissupportedby this type,whichwiththe presentdataareclassifiedasC—. at 10and405MHz.Itissuggestedthatinsuchsources therearetwocomponentswith the spectrumathighfrequencies);thisisoftenconfirmed bythefluxdensitiesmeasured at lowerfrequenciesaresystematicallythan thevaluespredictedbyextrapolating fact, veryfew3Csourcesbehaveinthisway,andsuggeststhatwhenasourceis made upofseveralcomponents,thespectralindicesandthuselectron-energydis- low frequencies.Wheneverthedifferentcomponentsofacomplexsourcehavesignifi- (that is,theindicesatlowandhighfrequenciesare nearlyequal,butthefluxdensities dominates athighfrequenciesandtheotherwithasteepspectrumwhich Most ofthesearethoughttobecompositespectracausedbytwoormorecomponents cantly differentspectralindices,theover-allspectrumwillshowpositivecurvature.In cases thesourceisknowntoconsistoftwocomponents,onewithaflatspectrumwhich 28 tributions ofthevariouscomponentsareusuallysimilar. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem For afewsourcesthespectra areextremelycomplexwithseveralmaximaand minima. Several sourcesshowmorecomplexspectraandwehaveclassifiedtheseasComplex. 3C c) Provisionalstandards(basedondirectcomparisonwithb): 3C 218a=-091±001S=580f.u. 3C 461(CasA)a=-0.765+0005Siooo=3090±30f.u. a) Primarystandard(basedonabsolutemeasurements): b) Secondarystandards(basedondirectcomparisonwithCasA): im KELLERMANN, PAULINY-TOTH,ANDWILLIAMS Spectra ofRadioSourcesSuitableforCalibration 270 263 348 -1.02+00160 441 351 349 272.1 249.1 227 223 223 353 -071+0.01700 274 -080+001266. 303 175 197 196 180 130 47 43 89 75 a= —071+001 -0.54+0.01 -0.98+0.01 -0 71+001 -0.75+0.02 —0.74+Ö.01 -0.58+0 01 -0 79+001 -0 80+002 -0 59+001 -0 78+0.01 -0.79+0 01 -0 73+001 -0 69+002 -0 96+001 -1 09+001 -0.82 +001 -0 82+001 -0 99+0.01 -0 73+001 iv) ClassCpx TABLE 5 Siooo= 3.48f.u. 21.0 4 13 9 10 3 86 3 18 3.88 4 10 3 26 2 94 2.23 2 44 5 13 7.10 2 63 3 46 3 40 3 81 3.31 7 73 Vol. 157 19 69ApJ. . . 157 IK 3 3 at adifferentfrequency.Sources3C84,3C273,3C345,and454.3havespectraofthis No. 1,1969 without doubtthesearegalacticHnregions.Inmostcasesthesourcesoptically Such spectraareprobablythesumofanumbercomponentseachwhichhascutoff far largerthantheestimateduncertaintiesincalibration. measured withrespecttothesurroundingbackgroundradiation,willbelessthan is attenuatedbyabsorptionsothattheapparentfluxdensityofanopticallythicksource, where thesourceisopticallythick,backgroundradiationobservedthrough corresponds toonecomponentonly. brightness temperaturewillcutoffatahigherfrequency, sothat,asdescribedin§V, given bytherelation, face brightnesssothatabsorptionbytherelativisticelectronscausessourceto 49, 3C303.1,305.1,and343343.1.Apparentlythesearerelativelysimple for theobserveddegreeofcurvature.Forexample,itwouldbepossibletoexplaina of theflux-densityscalesindifferentfrequencyranges,butthisisunlikelytoaccount and thefluxdensityofsourceremainsconstantdownto38MHz.Ininterpreting sources ofverysmallangulardiameterandhencehighsurfacebrightnesshavehighly spectra aresteeperathighfrequencies,withameandifferenceofabout0.12between true fluxdensity. cussed elsewhereinmoredetail(KellermannandPauliny-Toth1969). type. Theseandothersimilarsources,whichoftenshowlargetimevariations,aredis- different brightnesstemperatures.Insuchasource, thecomponentwithhigher where Sisthefluxdensityinunitsatafrequency vwheretheopticaldepthissmall, diameter ofthesource,0,andmagneticfieldwithinB(ingauss),as quency atwhichthefluxdensityisamaximum,j/(MHz),determinedbyangular become opticallythickbelowawell-definedcutofffrequency.Insuchsourcesthefre- sources inwhichmostoftheemissionoriginatesacomponentuniformlyhighsur- the low-frequencyspectrumhassameslope as thehigh-frequencyspectrumbut with populationsofrelativisticelectronshaving similar energyspectra,butwithvery 3C 138,147,and298;theradiogalaxy295;unidentifiedsources at lowfrequenciesisverysharp;theseincludethequasi-stellarsources3C48,119, curved spectra(Kellermannetal.1962).Insomesourcesofsmallangularsize,thecutoff systematically lowby40and18percent,respectively,orifthefluxdensitiesat1400, difference of0.12betweentheindicesiffluxdensitiesat38and178MHzwere the apparentspectrumofathermalsource,itmustberememberedthatatwavelengths thick atthelongerwavelengths,thoughinafewcasesemissionmeasureissmall shift ofthesource. 7 =l-2a,f\y)6.4X10fory1.5and4.5 X10fory=2.5,andzisthered- 2695, and5000MHzwerelowby8,1825percent,respectively:Sucherrorsare the indices.Suchacurvaturemaypartlybeduetosystematicerrorsincalibration as 10timeshigherthanthe cutofffrequency.Inothersourcesthereisagradual flatten- 3C 295,sometimesshow adefiniteflatteningofthespectrumatfrequencies asmuch temperature ofeachsourceisconsidered.Ithasbeenknownforsometimethatcertain to © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Sources classifiedashavingthermalspectraarefoundclosetothegalacticplane,and It isclearfromTable4thatforthemajorityofsourcesathighgalacticlatitudes Another straightforwardexampleoccurswhena source consistsoftwocomponents The probablecauseofthiscurvatureinthespectrumissuggestedwhenbrightness Some sourcesareevenmore complex.Severalwithasharpcutoff,suchas 3C 48and 02 /()B1/25(,),(7-1)/2^-(4+)/2()l/2(f )2^ =7jiï1 +0sec arc b) SpectralCurvature RADIO SOURCES v) ClassT 29 19 69ApJ. . . 157 IK 1 it isclearthatforthegreat majorityofquasi-stellarsourcesintherevised 3C catalogue included inFigure6orTable6.Eachofthecurves inFigure6hasbeenbroadened from thegalacticplane(b>10°).Themeanvalue oftheindex,,anditsdispersion, This isdiscussedfurther byKellermann,Pauliny-Toth,andTyler(1968) andby Pauliny-Toth andKellermann (1968).Thesecondpopulationofquasi-stellar sources, unusually flatspectra;thesehaveangulardiameters wellunder1",andinthesesources make acontributiontotheobservedspectralcurvature. mechanisms causeasteepeningofthespectrumathighfrequencies,andthereforemay mechanism, suchassynchrotronradiationlossesorinverseComptonscattering.These the distributionofspectral indicesisverysimilartothedistributionforradio galaxies. difference isentirelyduetoasmallproportion ofquasi-stellarsourceswhichhave by about10percenttheuncertaintiesinindividual spectralindices. original energydistributionofrelativisticelectronsmightbemodifiedbysomeother synchrotron self-absorptionislesslikelytobeafactor,theobservedrangeofspectral It mightbeexpected,therefore,thatinthefrequencyrange750-5000MHz,where upper limittotherangeofindicesdifferentialenergyspectrumelectrons. mined notonlybytheenergydistributionofrelativisticelectronsbutpartly 0.02, sothattheobservedspectralcurvatureappearstobelargelyconfinedsources frequencies a(5000-750)=—0.88+0.04forthesescintillatingsources,whileatlowfre- pass closetothesun,forty-twohaveascintillatingcomponentof20percentormoreat Hewish, Scott,andWills1964). at leastwecanbecertainthatsynchrotronself-absorption hasmadeamajorcontribu- than forradiogalaxies(WilliamsandCollins1967) andthedispersionisgreater.This Aa, areshowninTable6foreachgroup.Sources withuncertainidentificationsarenot indices wouldbesmaller.Infactitislarger,suggestingthatathighfrequenciesthe The observedrangeofindicesisdeterminedbybothfactors,andconsequentlysetsan tion incomponentswheretheopticaldepthissogreatthatfluxdensityat178MHz which containcomponentsofverysmalldiameterandhighsurfacebrightness.Some structure oftheorder1"orlesspassbehindsolarcorona(e.g.,Williams1964; observations ofinterplanetaryscintillationswhicharedetectedwhensourcescontaining ferometer observationsdoprovidedirectevidencethatsomesourcesofrelativelylow some estimateoftheextentsmall-scalestructureinextendedsourcesisprovidedby Bash 1968).Thereare,however,insufficienthigh-resolutioninterferometricdatato should produceaflatteningofthespectrumoversuchwiderangefrequencies, ing oftheslopebutnosharpcutoff,atleastabove38MHz.Inorderthatself-absorption tion totheflatteningofspectrumatlowfrequencies. Apartfromthesefewsources 750) separatelyforradiogalaxies,quasi-stellarsources, andunidentifiedsourcesaway synchrotron self-absorptionincomponentswithala4*gerangeofbrightnesstemperatures. the curvaturefoundinnon-scintillatingsourcesmayalsobecausedbyself-absorp- tain ascintillatingcomponent,therespectiveindicesare—0.83+0.03and—0.78± quencies themeanindexa(750-38)=—0.66±0.04.Forsourceswhichdonotcon- a diameterof1"orless(LittleandHewish1968).Themeanspectralindexathigh allow adetailedcomparisonofspectralcurvatureandsurfacebrightness.Nevertheless, average brightnesstemperaturecontainverysmall,brightcomponents(Wade1966; condition whichimpliesanextremelywiderangeofbrightnesstemperature.Inter- different partsofthesourcemustbecomeopticallythickatfrequencies,a 30 too lowforthescintillationstobedetected. 178 MHz,afactwhichindicatesthatatleast20percentoftheemissionisconfinedto © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem In bothfrequencyrangesthemeanindexforquasi-stellar sourcesismorepositive In Figure6wehaveplottedhistogramsofthedistributiona(750-38),anda(5000- Of eighty-sevensourcesselectedatrandomfromtherevised3Ccatalogueandwhich We thereforeconcludethattheformofradiospectruminmanysourcesisdeter- KELLERMANN, PAULINY-TOTH,ANDWILLIAMS c) ComparisonofRadioGalaxiesandQuasi-stellarSources Vol. 157 19 69ApJ. . . 157 IK n and 750MHz,(b)radiogalaxiesbetween5000{c)quasi-stellarsources38 frequencies, suchasthe408-MHzParkessurveys. No. 1,1969RADIOSOURCES31 steeper spectrathaneithertheradiogalaxiesorquasi-stellarsources,especially 10° between38and750MHz,(/)theunidentifiedsources5000MHz. 750 MHz,{d)quasi-stellarsourcesbetweenand5000(e)theunidentifiedwith|¿|> those withveryflatspectra,arefoundingreaternumberssurveysmadeathigher above 750MHz.Ashasbeenpointedoutelsewhere(Pauliny-TothandKellermann 1968), itisunlikelythatthesteeperspectrafoundforunidentifiedsourcesaredue © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Fig. 6.—Histogramsshowingthedistributionofspectralindicesfor{a)radiogalaxiesbetween38 The unidentifiedsourcesintherevised3Ccataloguearefoundtohavesystematically QSSs. Unidentified Sources. Galaxies. Mean SpectralIndexandDispersionforthe I 6- 1—i—i—i—i—i—i—— 38-750 MHz750-5000 Three GroupsofSources (a)= —0.753+0013 (a)= —0795+0022 (a)= —0700+0035 Aa= 0.193+0.014 Aa= 0242+0033 Aa= 0149+009 38-750 MHz TABLE 6 QSS (a)= —0969+0.020

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