mm-VLBI Observations of the Active Galaxy 3C 111 in Outburst

0.97 MB·English

by  Robert Schulz

mm-VLBI Observations of the Active Galaxy 3C111
in Outburst
Robert Schulz∗a,b, Matthias Kadlera, Eduardo Rosc,d, Thomas P. Krichbaumd,
3
1 Christoph Grossbergerb,a, Cornelia Müllerb,a, Karl Mannheima, Iván Agudoe,f, Hugh
0 D. Allerg, Margo F. Allerg
2
aLehrstuhlfürAstronomie,UniversitätWürzburg,CampusHublandNord,Emil-Fischer-Strasse

n
31,97074Würzburg,Germany
a
J bDr. RemeisSternwarte&ECAP,UniversitätErlangen-Nürnberg,Sternwartstr. 7,96049

8 Bamberg,Germany
2 cDepartamentd’AstronomiaiAstrofísica,UniversitatdeValència,46100Burjassot,València,

Spain
]
E dMax-Planck-InstitutfürRadioastronomie,AufdemHügel69,53121Bonn,Germany
H eInstitutodeAstrofísicadeAndalucía,CSIC,Apartado3004,18080,Granada,Spain
h. fInstituteforAstrophysicalResearch,BostonUniversity,725CommonwealthAvenue,Boston,
p MA02215,USA
- gDepartmentofAstronomy,UniversityofMichigan,817DennisonBuilding,AnnArbor,MI
o
r 48109-1042,USA
t
s
a
[ E-mail: [email protected]

1
v The broad-line radio galaxy 3C111 exhibited a major flux density outburst in 2007. Here, we
2
present imaging and preliminary kinematic results of the jet, based on three millimetre-VLBI
8
5 observationsat86GHzusingtheGlobalMillimeterVLBIArray(GMVA)coveringoneyearjust
6
aftertheradioflare. TheGMVAdataallowustostudythisoutburstwithunprecedentedimage
.
1
fidelityathighest(sub-parsec)resolution.Onthesescales,theoutburstisresolvedintoacomplex
0
3 series of plasma components forming an intriguing bent structure. Within 1mas from the jet
1 base,ejectionsvaryinpositionangleandcomponentsmovewithanapparentvelocityof∼3.7c,
:
v significantlyslowerthanthemaximumvelocityobservedwithcm-VLBIonscalesbeyond1mas.
i
X
r
a
11thEuropeanVLBINetworkSymposium&UsersMeeting,
October9-12,2012
Bordeaux,France
∗Speaker.
(cid:13)c Copyrightownedbytheauthor(s)underthetermsoftheCreativeCommonsAttribution-NonCommercial-ShareAlikeLicence. http://pos.sissa.it/
mm-VLBIObservationsoftheActiveGalaxy3C111inOutburst RobertSchulz
1. Introduction
The active galaxy 3C111 is a broad-line radio galaxy with a classic FRII morphology on
kpc-scales [4, 10] at a redshift of z=0.049. It has been extensively studied at all bands of the
electromagneticspectrum(e.g. [2,7,9]andreferencestherein). Long-termradiolightcurvesshow
3C111tobeastrongandvariablesource(e.g.,[15])withamajoroutburstabove10Jyat90GHz
in 1996 [1]. This led to the ejection of a new feature into the pc-scale jet, which shaped the jet
morphologyovertenyearsasseenon15GHzVLBAimages[9]. At15GHzand43GHzapparent
velocities of up to 6c were observed [2, 9]. The angle of the pc-scale jet to the line of sight at
15GHzand43GHzisrathersmallforaradiogalaxywithvaluesof∼15−20◦ [3,8,9].
2. Observation
In 2007, a major outburst comparable in strength to the one in 1996 occurred [15]. We per-
formedthreesuccessiveobservationson2007-10-13,2008-05-11and2008-10-14withtheGlobal
Millimeter VLBI Array (GMVA1) over a period of one year to study the jet evolution in response
to this event at the highest angular resolution. Table 1 gives an overview of the characteristics of
the GMVA antennas involved at the time of our observations, which included most of the avail-
ablemm-wavelengthradiotelescopesinEuropeandtheUSA.Withamaximumbaselineofabout
11000km,weachievedaresolutionof∼45µas,whichcorrespondstoaprojectedlinearscale2 of
∼0.043pcfor3C111.
The correlation of the GMVA data was performed with the VLBI correlator at the MPIfR
(Bonn, Germany). The Astronomical Imaging Processing System (AIPS) software package [5]
was used for the a-priori calibration. The delays and fringe rates of the interferometric phases
were corrected with the fringe-fitting algorithm. This step is especially important for mm-VLBI,
becauseofthedecreasingcoherencelengthoftheatmospherewithhigherfrequencies(see[13]for
more details). The measured system temperatures and antenna gains were applied for amplitude
calibration. Hybridimagingandmodel-fittingwasdoneinDIFMAP[14].
3. Results
Figure 1 shows images of 3C111 at 15, 43 and 86GHz, demonstrating the improved angular
resolution in going from cm-VLBA to mm-GMVA observations. The two top panels display the
straight jet morphology of 3C111, which is well known to extend out to kpc-scales [10]. This
showsthatthejetisalreadywellcollimatedattheresolutionlimitforVLBAobservationsat15GHz
(fromtheMOJAVEprogram3,see[11])and43GHz(fromtheBostonUniversitygamma-rayblazar
monitoringprogram4,see[12]). Thebottompaneldepictsthefirst86GHzGMVAepoch(2007-10-
13)closesttotheoutburstwithaprominentbendclearlyvisibleatabout0.5masfromthejetbase.
The angular resolution along the jet is foremost determined by the minor axis of the synthesized
1http://www.mpifr-bonn.mpg.de/div/vlbi/globalmm/
2AssumingH0=71kms−1Mpc−1,ΩΛ=0.73andΩm=0.27(1mas=0.95pc;1masyr−1=3.1c)
3http://www.physics.purdue.edu/MOJAVE/
4http://www.bu.edu/blazars/VLBAproject.html
2
mm-VLBIObservationsoftheActiveGalaxy3C111inOutburst RobertSchulz
Station Diameter SEFD Epoch1 Epoch2 Epoch3
[m] [Jy] 2007-10-13 2008-05-11 2008-10-14
Metsähovi 14 17647 (cid:88) (cid:88)2 X
Onsala 20 6122 (cid:88) (cid:88) (cid:88)
Effelsberg 100 929 (cid:88) (cid:88) (cid:88)
PlateaudeBure 35∗ 409 (cid:88) (cid:88)2 X
PicoVeleta 30 643 (cid:88)1 (cid:88) (cid:88)3
8×VLBA# 25 2941 (cid:88) (cid:88) (cid:88)4
Table1: ListoftheGMVAstationsin2007and2008withdiameter,systemequivalentfluxdensity(SEFD)
andparticipationinourobservations.
∗Equivalentdiameterofaphasedinterferometricarraywith6×15mtelescopes.
#TheeightVLBAstationsareNorthLiberty, FortDavis, LosAlamos, PieTown, KitPeak, OwensValley,
Brewster,MaunaKea.
1Nofringesaftercorrelation,2Flaggedduringa-prioricalibration,3Datawerelostduetobadwheather,4Data
ofNorthLibertyandFortDaviswereflaggedduringhybridimaging.
beam, leading to an improvement in resolution from 15GHz VLBA to 86GHz GMVA by about
oneorderofmagnitude.
Allthree86GHzimagesarecombinedintheleftpanelofFig. 2,wheretherightpanelshows
the(u,v)-coverageofeachobservation,resultinginunprecedentedimagefidelityfor3C111atthis
frequency. Onsuchsmallscales,thejetevolvesdramaticallyovertheperiodofoneyear. Thebend
moves radially away from the core, but remains among the strongest features within the jet in all
threeobservations. Thecontributionoftheinner0.1masregiontothetotalemissionishighestfor
the third epoch (bottom panel). Interestingly, the jet stream between the core and the bend stays
rather straight in the second and third epoch, albeit at a different position angle than in the first
epoch.
A kinematic analysis was performed to study the jet evolution in detail. For this purpose,
additional15epochsofarchival43GHzVLBAdatafromtheBostonUniversitygamma-rayblazar
monitoringprogrambetweenJune2007andFebruary2009weremodel-fittedforcomparison. The
complete analysis will be presented elsewhere (R. Schulz et al. in prep.). Preliminary results
stronglysuggestthatthebentfeatureisassociatedwiththeoutburstin2007. Atbothfrequencies,
thisfeaturehasapositionanglebetween75◦ to80◦,whilethepositionanglesoftherestofthejet
remainaround60◦ to70◦. At86GHz,thebendseemstotravelwithanapparentvelocityofabout
∼3.7c (see Fig. 2), which is significantly slower than the highest apparent velocity observed on
larger scales at 15 and 43GHz [8, 9]. A complementary long-term study of 3C111 is addressing
thejetmorphologyat15GHzbasedonVLBAdatafromtheMOJAVEprogram[6].
4. Summary
We present here images of 3C111 based on three successive observations with the Global
Millimeter VLBI Array at 86GHz following a major outburst in 2007. The images are of un-
precedented quality for this object at this frequency, revealing a rapidly evolving bent feature in
the jet. Preliminary kinematic results indicate that this bend is related to the outburst in 2007. It
3
mm-VLBIObservationsoftheActiveGalaxy3C111inOutburst RobertSchulz
Figure 1: Zoom into 3C111. Top: 15GHz VLBA image (2007-09-06) with a synthesized beam of
0.90×0.56mas2 at −1◦ and a peak flux density of 3.23Jy/beam; Middle: 43GHz VLBA image (2007-
09-29)withasynthesizedbeamof0.36×0.18mas2at−1◦andapeakfluxdensityof3.36Jy/beam;Bottom:
86GHzGMVAimage(2007-10-13)withasynthesizedbeamof0.15×0.045mas2 at−11◦ andapeakflux
density of 1.50Jy/beam. The lowest contour lines are set to 5σ of the rms noise for the first, second and
third image respectively, increasing logarithmically by factors of two. The axes show distances relative to
thepositionofthepeakemissioninunitsofmas.
moveswithadifferentpositionanglethanotherjetfeaturesandwithasignificantlylowerapparent
velocitythanhigher-velocityfeaturestypicallyobservedonscalesbeyond1masinthissource.
Acknowledgments
This study makes use of 43 GHz VLBA data from the Boston University gamma-ray blazar
monitoringprogram(http://www.bu.edu/blazars/VLBAproject.html),fundedbyNASAthroughthe
FermiGuestInvestigatorProgram. ThisresearchhasmadeuseofdatafromtheMOJAVEdatabase
that is maintained by the MOJAVE team [11]. The GMVA data are correlated at the VLBI corre-
lator of the MPIfR, Bonn, Germany. The Very Long Baseline Array (VLBA) is an instrument of
the National Radio Astronomy Observatory (NRAO). NRAO is a facility of the National Science
Foundation, operated by Associated Universities Inc. ER acknowledges partial support from the
4
mm-VLBIObservationsoftheActiveGalaxy3C111inOutburst RobertSchulz
Spanish MINECO through grant AYA2009-13036-C02-02, from the Generalitat Valenciana grant
PROMETEO-2009-104,andbytheCOSTactionMP0905‘BlackHolesinaViolentUniverse’.
References
[1] W.Alef,E.Preuss,K.I.Kellermann,etal.,Sub-milliarcsecStructureof3C111at0.7and3.6CM,
ASPConf.Ser.144IAUColloq.164: RadioEmissionfromGalacticandExtragalacticCompact
Sources(1998)129
[2] R.Chatterjee,A.P.Marscher,S.G.Jorstad,etal.,ConnectionBetweentheAccretionDiskandJetin
theRadioGalaxy3C111,ApJ734(2011)43[arXiv:1104.0663]
[3] M.H.Cohen,M.L.Lister,D.C.Homan,etal.,RelativisticBeamingandtheIntrinsicPropertiesof
ExtragalacticRadioJets,ApJ658(2007)232[arXiv:astro-ph/0611642]
[4] B.L.Fanaroff,J.M.Riley,Themorphologyofextragalacticradiosourcesofhighandlowluminosity,
MNRAS167(1974)31
[5] E.W.Greisen,AIPS,theVLA,andtheVLBA,InformationHandlinginAstronomy-HistoricalVistas
285(2003)109
[6] C.Grossberger,M.Kadler,J.Wilms,etal.,StructuralVariabilityof3C111onParsecScales,AcPol
52(2012)18,[arXiv:1110.1197]
[7] R.C.Hartman,M.Kadler,J.Tueller,Gamma-RayEmissionfromtheBroad-LineRadioGalaxy3C
111,ApJ688(2008)852[arXiv:0808.1740]
[8] S.G.Jorstad,A.P.Marscher,M.L.Lister,etal.,PolarimetricObservationsof15ActiveGalactic
NucleiatHighFrequencies: JetKinematicsfromBimonthlyMonitoringwiththeVeryLongBaseline
Array,AJ130(2005)1418[arXiv:astro-ph/0502501v3]
[9] M.Kadler,E.Ros,M.Perucho,etal.,TheTrailsofSuperluminalJetComponentsin3C111,ApJ680
(2008)867[arXiv:0801.0617]
[10] R.Linfield,R.Perley,3C111-Aluminousradiogalaxywithahighlycollimatedjet,ApJ279(1984)
60
[11] M.L.Lister,H.D.Aller,M.F.Aller,etal.,MOJAVE:MonitoringofJetsinActiveGalacticNuclei
withVLBAExperiments.V.Multi-EpochVLBAImages,AJ137(2009)3718[arXiv:0812.3947]
[12] A.Marscher,S.G.Jorstad,V.M.Larionov,etal.,Multi-WavebandEmissionMapsofBlazars,JApA
32(2011)233[arXiv:1101.0179]
[13] I.Martí-Vidal,T.P.Krichbaum,A.Marscher,etal.,Onthecalibrationoffull-polarization86GHz
globalVLBIobservations,A&A542(2012)A107[arXiv:1203.1424]
[14] M.C.Shepherd,T.J.Pearson,G.B.Taylor,DIFMAP:aninteractiveprogramforsynthesisimaging.,
BAAS26(1994)987
[15] S.Trippe,M.Krips,V.Piétu,etal.,Thelong-termmillimeteractivityofactivegalacticnuclei,A&A
533(2011)A97[arXiv:1107.5456]
5
mm-VLBIObservationsoftheActiveGalaxy3C111inOutburst RobertSchulz
Figure2: Leftpanel: Overviewofallthree86GHzGMVAepochsof3C111,obtainedwithhybridimag-
ingandnaturalweightingofthevisibilitydata: Top: Firstepoch(2007-10-13)withasynthesizedbeamof
0.15×0.045mas2 at−10.8◦ andapeakfluxdensityof1.50Jy/beam; Middle: Secondepoch(2008-05-11)
with a synthesized beam of 0.15×0.059mas2 at −15.5◦ and a peak flux density of 0.39Jy/beam; Bottom:
Thirdepoch(2008-10-14)withasynthesizedbeamof0.17×0.067mas2 at−18.2◦ andapeakfluxdensity
of1.87Jy/beam. Thelowestcontourlinesrepresent10σ (firstimage)and5σ (secondandthirdimage)of
thermsnoise,increasinglogarithmicallybyfactorsoftwo. Theimagesarespacedaccordingtothesepara-
tionoftheobservationsintimeandhavebeenspatiallyalignedtothejetcore,wheretheemissionbecomes
opticallythick. Theaxisshowsdistancesrelativetothecore. Thecolouredlinesindicatetheevolutionof
associatedfeaturesbetweentheepochsbasedonthepreliminarykinematicanalysis.
Right panel: (u,v)-coverage of the GMVA for the images in the left panel. The longest baselines con-
nectsthePlateaudeBureInterferometer(France)andMaunaKea(HI,USA),whichgivesa(u,v)-radiusof
∼3100Mλ correspondingto∼45µasinangularresolution.
6