J/A+A/658/A8ivo://CDS.VizieR/J/A+A/658/A8doi:10.26093/cds/vizier.36580008CDSHarwood J.J.Mooney S.Morabito L.K.Quinn J.Sweijen F.,Groeneveld C.Bonnassieux E.Kappes A.Moldon J.2022-08-25T11:26:24Z2022-01-25T08:46:54ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frquasarsactive-galactic-nucleiradio-sourcesSince its discovery in 1963, 3C 273 has become one of the most widely studied quasars with investigations spanning the electromagnetic spectrum. While much has therefore been discovered about this historically notable source, its low-frequency emission is far less well understood. Observations in the MHz regime have traditionally lacked the resolution required to explore small-scale structures, such as knots and diffuse jet emission, that are key to understanding the processes that result in the observed emission. Advances in the processing of LOFAR international baseline data have now removed this limitation, providing the opportunity to explore this key area for the first time. In this paper we use the first sub-arcsecond images of 3C 273 at MHz frequencies to investigate the morphology of the compact jet structures and the processes that result in the observed spectrum. We will determine the jet's kinetic power, place constraints on the bulk speed and inclination angle of the jets, and look for evidence of the elusive counterjet at 150MHz. Using the full complement of LOFAR's international stations (German, Poland, France, UK, Sweden), we produce 0.31x0.21 arcsec images of 3C 273 at 150MHz. Using ancillary data at GHz frequencies, we fit free-free absorption (FFA) and synchrotron self-absorption (SSA) models to each region in order to determine their validity in explaining the observed spectra. The images presented display for the first time that robust, high-fidelity imaging of low-declination complex sources is now possible with the LOFAR international baselines. We show that the main small-scale structures of 3C 273 match those seen at higher frequencies, with a tenuous detection of an extension to the outer lobe. We find that FFA and SSA models are able to describe the spectrum of the knots and, while differentiating between model types requires further observations, conclude that absorption is present in the observed emission. We determine the kinetic power of the jet to be in the range of 3.5x10^43^-1.5x10^44^erg/s which agrees with estimates made using higher frequency observations. We derive lower limits for the bulk speed and Lorentz factor of beta>0.55 and Gamma>1.2 respectively. The counter-jet remains undetected at 150MHz, placing a limit on the peak brightness of S_cj_150<40mJy/beam.2022A&A...658A...8Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/658/A8CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/MNRAS/392/1181 : BV(RI)c photometry of 3C 273 (Dai+, 2009)J/ApJS/213/26 : Optical light curves of PHL1811 and 3C273 (Fan+, 2014)J/A+A/576/A122 : 3C 273 high energy spectrum (Esposito+, 2015)J/A+A/601/A35 : High-fidelity VLA imaging of 3C273 (Perley+, 2017)J/ApJS/229/21 : VRI monitoring of the QSO 3C 273 in 2005-2016 (Xiong+, 2017)J/A+A/604/A111 : 22GHz image of 3C 273 (Bruni+, 2017)J/ApJ/876/49 : 10yr reverberation mapping campaign for 3C273 (Zhang+, 2019)J/ApJ/880/155 : RI photometry of blazars S5 0716+714 and 3C 273 (Liu+, 2019)J/A+A/636/A62 : Light curves of 3C273 during 2015-2019 (Kim+, 2020)J/AJ/159/259 : Opt-NIR light curve of 3C 273 (Sobrino Figaredo+, 2020)J/ApJ/897/18 : Swift UVOT observation of radio quasar 3C 273 (Li+, 2020)J/A+A/658/A2 : LOFAR Long-Baseline Calibrator Survey. II. (Jackson+, 2022)J/A+A/658/A4 : LOFAR imaging of Arp299 at 150MHz (Ramirez-Olivencia, 2022)J/A+A/658/A5 : Hercules A LOFAR and JVLA images (Timmerman+, 2022)J/A+A/658/A6 : 3C293 high and low resolution maps (Kukreti+, 2022)J/A+A/658/A10 : 3C295 LOFAR, MERLIN and VLA images (Bonnassieux+, 2022)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/658/A8https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/658/A8http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/658/A8https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/658/A8https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/658/A8http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/658/A8GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/658/A8/list (Information on fits image)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/658/A8/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/658/A8/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/658/A8/list?GETtext/xml+votable180.050000true187.273842.048270.005555555555555556Associated datahttps://cdsarc.cds.unistra.fr/assocdata/?obs_collection=J/A+A/658/A86/262929.939104750406538e-26 9.939104750406538e-26https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/658/A8?format=asciiRadiodefaultJ/A+A/658/A8/table2Flux densities and spectral index valuesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFeatureJet structure labelmeta.id;meta.maincharl_S150Limit flag on S150meta.code.errorcharS150Flux density at 150MHzJyphot.flux.density;em.radio.100-200MHzfloate_S150? Flux density at 150MHz uncertaintyJystat.errorfloatnullablealpha? Spectral index between 150MHz and 8330MHz, alpha_150_^8330^spect.index;em.radio.100-200MHzfloatnullablee_alpha? Spectral index uncertaintystat.error;pos.eq.rafloatnullableJ/A+A/658/A8/table3Free-free and synchrotron self-absorption model fitting valuesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFeatureJet structure labelmeta.id;meta.maincharl_taunu0Limit flag on taunu0meta.code.errorchartaunu0FFA optical depth at a reference of 150MHzphot.flux.density;em.radio.100-200MHzfloate_taunu0? taunu0 uncertaintystat.errorfloatnullablel_nupLimit flag on nupmeta.code.errorcharalphaFFAFree-free absorption index (+/-0.03)spect.indexfloatnupFrequency at which the region becomes optically think for the SSA modelMHzem.freqfloate_nup? nup uncertaintyMHzstat.errorfloatnullablealphaSSASynchrotron-self absorption index (+/-0.03)spect.indexfloatJ/A+A/658/A8/listInformation on fits imagerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberintNyNumber of pixels along Y-axismeta.numberintObs.dateObservation datestime.epoch;obsnullableFreqObserved frequencyMHzem.freqfloatsizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitscharJ/A+A/658/A8/listimgList of png imagesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFileNameName of the png image, in subdirectory imgmeta.id;obs.imagecharTitleTitle of the file, in subdirectory imgmeta.title;meta.filechar