J/A+A/690/A74ivo://CDS.VizieR/J/A+A/690/A74doi:10.26093/cds/vizier.36900074CDSGiarratana S.Salafia O.S.Giroletti M.Ghirlanda G.Rhodes L.Atri P.,Marcote B.Yang J.An T.Anderson G.Bright J.S.Farah W.Fender R.,Leung J.K.Motta S.E.Perez-Torres M.van der Horst A.J.2025-02-18T20:01:43Z2024-10-02T09:08:34ZCDS support team

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

cds-question@unistra.frgamma-ray-astronomygamma-ray-burstsinterferometryvery-long-baseline-interferometryradio-continuum-emissionWe observed gamma-ray burst (GRB) 221009A using very long baseline interferometry (VLBI) with the European VLBI Network (EVN) and the Very Long Baseline Array VLBA), over a period spanning from 40 to 262 days after the initial GRB. The high angular resolution (mas) of our observations allowed us, for the second time ever, after GRB 030329, to measure the projected size, s, of the relativistic shock caused by the expansion of the GRB ejecta into the surrounding medium. Our observations support the expansion of the shock with a>4sigma-equivalent significance, and confirm its relativistic nature by revealing an apparently superluminal expansion rate. Fitting a power law expansion model, s~t^a^, to the observed size evolution, we find a slope a=0.69^+0.13^_-0.14_. Fitting the data at each frequency separately, we find different expansion rates, pointing to a frequency-dependent behaviour. We show that the observed size evolution can be reconciled with a reverse shock plus forward shock, provided that the two shocks dominate the emission at different frequencies and, possibly, at different times.2024A&A...690A..74Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/690/A74CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/690/A74https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/690/A74http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/690/A74https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/690/A74https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/690/A74http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/690/A74GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/690/A74/list (List of fits visibilities files)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/690/A74/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/690/A74/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/690/A74/list?GETtext/xml+votable180.050000true288.2664619.772940.0055555555555555566/32091https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/690/A74?format=asciiGamma-rayRadiodefaultJ/A+A/690/A74/listList of fits visibilities filesTitleTitle of the FITS filemeta.title;meta.fitscharFreqObserved frequencyGHzem.freqdoubleFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainNyNumber of pixels along Y-axismeta.numberintNzNumber of pixels along Z-axismeta.numberintObs.dateObserved datestime.epochnullablesizeSize of FITS fileKibytephys.size;meta.fitsintDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberint