Recently Jamrozy et al. (2009) identified 4C 02.27 (J0935+0204) as the first
possible example of a double-double radio source which is optically identified
with a quasar (i.e. not a galaxy), at the redshift of z=0.649. The overall
projected angular size of the radio source reaches about 1.5', with a prominent
"core" component in the centre. The two opposite pairs of radio lobes might
indicate two periods of episodic activity. We report on our short exploratory
1.6-GHz Very Long Baseline Interferometry (VLBI) observations of the innermost
radio structure of the quasar, conducted with the electronic European VLBI
Network (e-EVN) on 2009 September 30. These revealed a milliarcsecond-scale
compact source which is the base of the approaching one of the two symmetric
relativistic jets currently supplying the hot spots in the inner pair of the
arcsecond-scale radio lobes in 4C 02.27.Comment: 4 pages, 2 figures, to appear in the proceedings of the 10th European
  VLBI Network Symposium (September 20-24, 2010, Manchester, UK). Proceedings
  of Science (http://pos.sissa.it), PoS(10th EVN Symposium)07

Frey, S.

Paragi, Z.

English

arXiv

Recently Jamrozy et al. (2009) identified 4C 02.27 (J0935+02
04) as the first possible example of a double-double radio source which is optically identified with a quasar (i.e. not a galaxy), at the redshift of z=0.649. The overall projected angular size of the radio source reaches about 1.5′, with a prominent "core" component in the centre. The two opposite pairs of radio lobes might indicate two periods of episodic activity. We report on our short exploratory 1.6-GHz Very Long Baseline Interferometry (VLBI) observations of the innermost radio structure of the quasar, conducted with the electronic European VLBI Network (e-EVN) on 2009 September 30. These revealed a milliarcsecond-scale compact source which is the base of the approaching one of the two symmetric relativistic jets currently supplying the hot spots in the inner pair of the arcsecond-scale radio lobes in 4C 02.27

Frey, Sándor

Paragi, Zsolt

ZENODO

PoS(10th EVN Symposium)0774C 02.27: what is inside a double-double radioquasar?Sándor Frey∗†FÖMI Satellite Geodetic Observatory, P. O. Box 585, H-1592 Budapest, HungaryMTA Research Group for Physical Geodesy and Geodynamics, Budapest, HungaryE-mail: frey@sgo.fomi.huZsolt ParagiJoint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The NetherlandsMTA Research Group for Physical Geodesy and Geodynamics, Budapest, HungaryE-mail: zparagi@jive.nlRecently Jamrozy et al. (2009) identified 4C 02.27 (J0935+0204) as the first possible exampleof a double-double radio source which is optically identified with a quasar (i.e. not a galaxy),at the redshift of z=0.649. The overall projected angular size of the radio source reaches about1.5′, with a prominent “core” component in the centre. The two opposite pairs of radio lobesmight indicate two periods of episodic activity. We report on our short exploratory 1.6-GHz VeryLong Baseline Interferometry (VLBI) observations of the innermost radio structure of the quasar,conducted with the electronic European VLBI Network (e-EVN) on 2009 September 30. Theserevealed a milliarcsecond-scale compact source which is the base of the approaching one of thetwo symmetric relativistic jets currently supplying the hot spots in the inner pair of the arcsecond-scale radio lobes in 4C 02.27.10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radioarraysSeptember 20-24, 2010Manchester, UK∗Speaker.†The EVN is a joint facility of European, Chinese, South African, and other radio astronomy institutes funded bytheir national research councils. The e-VLBI research infrastructure in Europe is supported by the European Commu-nity’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. RI-261525 NEXPReS. This workwas supported by the European Community’s Seventh Framework Programme, Advanced Radio Astronomy in Europe,grant agreement no. 227290, and the Hungarian Scientific Research Fund (OTKA, grant no. K72515). This researchhas made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory,California Institute of Technology, under contract with the National Aeronautics and Space Administration.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/PoS(10th EVN Symposium)0774C 02.27: what is inside a double-double radio quasar? Sándor Frey1. IntroductionThe activity of galactic nuclei in the radio lasts for up to ∼106 years, therefore is episodiccompared to the whole lifetime of an object, which could be orders of magnitude longer. The radiojet activity could also be recurrent, as suggested by several cases where two or even three alignedpairs of radio lobes are observed in the opposite sides of a central active galactic nucleus (AGN),at different separations. The relic lobes provide “historical” information on different activity cy-cles via e.g. their spectra, brightness, polarisation properties, size, and location. A comprehensivereview of the observational evidence of recurrent activity in AGNs is found in [8], where 15 ex-amples of double-double radio galaxies and one triple-double radio galaxy are collected from theliterature.Recently [4] identified 4C 02.27 (J0935+0204) as the first possible example of a double-doubleradio quasar (DDRQ). Its redshift is z=0.649 as measured in the Sloan Digital Sky Survey [1]. Theouter pair of lobes can easily be identified in the 1.4-GHz radio image (Fig. 1) taken in the USNational Radio Astronomy Observatory (NRAO) Very Large Array (VLA) Faint Images of theRadio Sky at Twenty-centimeters (FIRST) survey [11]. The inner lobes, of which the north-east(NE) one is the brightest, are not well resolved in the FIRST image and are blended together with acentral “core” component. A VLA A-array image obtained at the same frequency [3] indicate thatthe separation of the inner lobes is nearly 10′′.CONT: J093518+  4C02.27.FIRST.1Cont peak flux =  2.0519E-01 JY/BEAM DECLINATION (J2000)RIGHT ASCENSION (J2000)09 35 23 22 21 20 19 18 17 16 15 1402 05 30150004 4530150003 453015coreNE_outSW_outNE_innSW_innFigure 1: 1.4-GHz radio image of 4C 02.27 from the VLA FIRST survey [11]. The lowest contours aredrawn at ±0.56 mJy/beam (3σ image noise). The positive contour levels increase by a factor of 2. The peakbrightness is 205.19 mJy/beam. The Gaussian restoring beam (6.4′′×5.4′′, major axis position angle 0o) isshown in the bottom-left corner. The components are labelled according to [4].There is a large brightness and arm-length asymmetry between the inner and outer pairs oflobes. This suggests that environmental asymmetries and relativistic motion together determinethe appearance of this source. An alternative explanation could be a jet reorientation between thecorresponding two cycles of activity, although it is less likely because of the special geometryrequired by the good alignment of the inner and outer lobes in the sky [4]. It was found that the2PoS(10th EVN Symposium)0774C 02.27: what is inside a double-double radio quasar? Sándor Freya bulk plasma velocity of ∼0.4c and a jet inclination of ∼40o with respect to the line of sight areconsistent with the observed arcsecond-scale inner structure. In this scenario, the inner NE lobe isapproaching to us.While the source extends to almost 1.5′, there is a “core” component with a flux density of∼90 mJy at 1.4 GHz, and a rather flat radio spectrum (inferred from other VLA data at higherfrequencies: [9, 6, 2]). The position of the radio core nearly coincides with the quasar’s opticalposition. 4C 02.27 has also been detected in X-rays with ROSAT [10].2. Observations and resultsThe source has never been imaged with Very Long Baseline Interferometry (VLBI) before.With the experiment described below, our goal was to detect any possible compact radio fea-ture in the central component on ∼10-milli-arcsecond (mas) angular scale with the EuropeanVLBI Network (EVN). To this end, short 2-h exploratory e-EVN observations were initiated.The project RSF03 took place on 2009 September 30, involving radio telescopes at Effelsberg(Germany), Medicina (Italy), Onsala (Sweden), Torun´ (Poland), Jodrell Bank Mk2, Cambridge,Knockin (United Kingdom), and the phased array of the Westerbork Synthesis Radio Telescope(The Netherlands). The observations were done at 1.6 GHz frequency, with the maximum band-width of 64 MHz in both left and right circular polarizations. The EVN Data Processor (JointInstitute for VLBI in Europe, Dwingeloo, The Netherlands) performed the correlation in real time.Figure 2: 1.6-GHz phase-referenced e-EVN image of 4C 02.27. The lowest contours are drawn at±0.25 mJy/beam. The positive contour levels increase by a factor of 2. The peak brightness is60.7 mJy/beam. The Gaussian restoring beam (42.5 mas×26.7 mas, major axis position angle 23o) is shownin the bottom-left corner. The absolute equatorial coordinates of the brightness peak (J2000 right ascension09h35m18.1946s and declination 02o04′15.558′′) are within the accuracy of 2 mas.The target source 4C 02.27 was observed in phase-reference mode, using the nearby calibratorJ0930+0034 (1.85o far away). The NRAO Astronomical Image Processing System (AIPS) wasused for data calibration and fringe-fitting in a standard way. It turned out that 4C 02.27, a compactsource on VLBI scale with ∼60 mJy correlated flux density, could itself be fringe-fitted as well.3PoS(10th EVN Symposium)0774C 02.27: what is inside a double-double radio quasar? Sándor FreyThe imaging, self-calibration, and model-fitting were done with the Caltech Difmap package. Herewe present the image obtained with phase-referencing (Fig. 2), which is practically identical to thatresulted from direct fringe-fitting to the target source data.According to our e-EVN image, the core of 4C 02.27 is compact, slightly extended to NE. Itsbrightness distribution is well described by a central circular Gaussian component (60.8 mJy fluxdensity, 1.6 mas diameter, full width at half maximum) and a weak extension (1.6 mJy, 20 mas)at the position angle of 47o, separated by 32 mas from the central one. The inferred rest-framebrightness temperature of the compact feature is 1.7×1010 K. Assuming the equipartition value of5×1010 K for the intrinsic brightness temperature [7], it is consistent with the ∼40o inclinationsuggested by [4] and a reasonable jet bulk Lorentz factor ∼12. The apparently one-sided jet-likestructure indicates that the NE side is the approaching one, just as deduced from the appearance ofthe inner lobes [4].3. DiscussionWith VLBI we observe the base of the approaching relativistic jet in 4C 02.27, a currentlyactive radio quasar. The jets provide the energy supply for the hot spots in the inner pair of thearcsecond-scale radio lobes seen in the VLA images. The asymmetry of the inner lobes is mostlikely caused by relativistic beaming effects. There is no need to invoke extreme misalignmentbetween the mas-scale and arcsecond-scale structures. At the resolution provided by the e-EVNat 1.6 GHz, we found no sign of an innermost double structure (unlike e.g. [5], in the case of theradio galaxy B0818+214) which would have indicated a third and most recent cycle of activity inthis unique radio-loud quasar.The appearance of the outer lobes is probably determined by environmental asymmetriesand/or light travel time effects. We see a later evolutionary stage of the fading outer lobe in theapproaching side (NE_out), it could therefore appear fainter than its counterpart on the recedingside (SW_out). Considering an aligned source geometry with ∼40o inclination to the line of sight,the light travel time difference is nearly 2×106 years between the two outer lobes.References[1] Abazajian K.N., Adelman-McCarthy J.K., Agüeros M.A., et al. 2009, ApJS 182, 543[2] Bogers W.J., Hes R., Barthel P.D., Zensus J.A. 1994, A&AS 105, 91[3] Hintzen P., Ulvestad J., Owen F. 1983, AJ 88, 709[4] Jamrozy M., Saikia D.J., Konar C. 2009, MNRAS 399, L141[5] Marecki A., Szablewski M. 2009, A&A 506, L33[6] Price R., Gower A.C., Hutchings J.B., et al. 1993, ApJS 86, 365[7] Readhead A.C.S. 1994, ApJ 426, 51[8] Saikia D.J., Jamrozy M. 2009, Bull. Astron. Soc. India 37, 63[9] Swarup G., Sinha R.P., Hilldrup K. 1984, MNRAS 208, 813[10] Voges W., Aschenbach B., Boller T., et al. 2000, IAU Circ. 7432[11] White R.L., Becker R.H., Helfand D.J., Gregg M.D. 1997, ApJ 475, 4794

4C 02.27: what is inside a double-double radio quasar?

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4C 02.27: what is inside a double-double radio quasar?

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