We have compiled a complete set of VSOP observations of 3C279, consisting of eight 5 GHz, and six 1.6 GHz, VSOP observations, all of which include the VLBA in the ground array. We are using the data-set to determine brightness temperature limits from model-fits to the visibilities, the transverse structure of the jet over its first 20 milliarcseconds, and parsec-scale spectral index maps

Edwards, P. G.

Hirabayashi, H.

Pant, N. D.

Piner, B. G.

Unwin, S. C.

Wehrle, A. E.

English

Poet Commons (Whittier College)

Whittier College Poet Commons Physics Faculty Publications & Research 2009 A Complete Set of VSOP Observations of 3C279 N. D. Pant B. G. Piner Whittier College, gpiner@whittier.edu P. G. Edwards H. Hirabayashi A. E. Wehrle See next page for additional authors Follow this and additional works at: https://poetcommons.whittier.edu/phys Recommended Citation Pant, N. D., Piner, B. G., Edwards, P. G., Hirabayashi, H., Wehrle, A. E., & Unwin, S. C. (2009). A Complete Set of VSOP Observations of 3C279. Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and Technologies, ASP Conference Series, Vol. 402, 213. Retrieved from https://poetcommons.whittier.edu/phys/36 This Conference Paper is brought to you for free and open access by the Faculty Publications & Research at Poet Commons. It has been accepted for inclusion in Physics by an authorized administrator of Poet Commons. For more information, please contact library@whittier.edu. Authors N. D. Pant, B. G. Piner, P. G. Edwards, H. Hirabayashi, A. E. Wehrle, and S. C. Unwin This conference paper is available at Poet Commons: https://poetcommons.whittier.edu/phys/36 Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and TechnologyASP Conference Series, Vol. 402, c© 2009Y. Hagiwara, E. Fomalont, M. Tsuboi, and Y. Murata, eds.A Complete Set of VSOP Observations of 3C279N. D. Pant,1 B. G. Piner,1 P. G. Edwards,2 H. Hirabayashi,3 A. E.Wehrle,4 S. C. Unwin5Abstract. We have compiled a complete set of VSOP observations of 3C279,consisting of eight 5 GHz, and six 1.6 GHz, VSOP observations, all of whichinclude the VLBA in the ground array. We are using the data-set to determinebrightness temperature limits from model-fits to the visibilities, the transversestructure of the jet over its first 20 milliarcseconds, and parsec-scale spectralindex maps.1. IntroductionThe radio source 3C279 has been well studied with ground observations over thelast 15 years (Piner et al. 2003; Homan et al. 2003; Ojha et al. 2004; Jorstad etal. 2004) with increased interest in the source following its rapid, bright flaresat >100 MeV gamma-ray energies (Wehrle et al. 1998).VSOP observations 3C279 were made between January 1998 and January2001 as part of the proposals v147, w094, and w088. A log of the observationsis given in Table 1. The first epoch observations were described in Edwards etal. (1999), Hirabayashi et al. (2000a), and Piner et al. (2000a, 2000b). Secondepoch observations described in Hirabayashi et al. (2000b). A priori calibrationand fringe fitting of all data was carried out in AIPS, and images produced inDifmap.2. ImagesThe 5 GHz VSOP images are dominated by the compact core and inner jet anda bright component at 4 mas from the core (see Figure 1). The jet component,labeled C4, has been followed since its ejection in late 1984. Jorstad et al. (2004)present a high-resolution multi-epoch VLBA study of this inner jet region.The 1.6 GHz images show the core and C4 and a more diffuse jet to thesouthwest. Strongly tapering the image to provide maximum sensitivity to morediffuse emission (effectively excluding the space baselines) allows the jet to be1Department of Physics and Astronomy, Whittier College, Whittier, CA 90608, USA2CSIRO/ATNF, Narrabri, NSW 2390, Australia3ISAS/JAXA, Sagamihara, Kanagawa 229-8510, Japan4Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 USA5JPL, 4800 Oak Grove Drive, Pasadena, CA 91101, USA213214 Pant et al.Table 1. Observation LogObservation code Date Frequency (GHz)v147a 1998 Jan 09 1.6v147b1 1998 Jan 10 4.8w094b1 1999 Mar 15 5.0w094b2 1999 Apr 09 4.8w088d1 1999 Apr 14 1.6w094b3 1999 May 12 4.9w088d2 1999 Jun 26 1.6w094b4 1999 Jul 06 4.9w094b5 2000 Mar 30 4.8w094b6 2000 Mar 31 4.9w088d3 2000 Apr 01 1.6w088d4 2000 Apr 02 1.6w094b7 2001 Jan 10 5.0w088d5 2001 Jan 11 1.6traced out to ∼100mas from the core, connecting it to the innermost jet structureobserved in VLA images (de Pater and Perley 1983).3. Brightness TemperaturesModel-fitting of the images was performed in VSOP DIFMAP with HALCAdata up-weighted to contribute equally to the ground data (Lovell et al. 2004).Errors on the size and flux density of the Gaussian components were determinedusing the DIFWRAP package (Lovell 2000). Brightness temperatures and lowerlimits were computed from these models. The median brightness temperaturelower limits for the core were 2.3×1012 K at 1.6 GHz and 4.4×1012 K at 5 GHz.For C4, the median brightness temperature lower limits were 1.0×1012 K at1.6 GHz and 3.7×1012 K at 5 GHz.4. Spectral Image MapsSpectral index maps were produced using the 1.6 GHz VSOP images and the5 GHz VLBA-only images as these have nearly matched resolutions.There were five epochs at which observations at both frequencies occurredwithin a 10 day period. Images were aligned on the peak of C4 to avoid theeffects of the expected frequency-dependent core shifts in the core.The spectral index at the eastern-most end of the core region approaches thetheoretical limiting value for synchrotron self-absorption of α=2.5 (for S ∝ ν+α),implying a very compact core region. Images will be presented elsewhere.VSOP Observations of 3C279 215Figure 1. VSOP image of 3C279 at 4.8 GHz from 2000 Mar 30. Image peakis 4.5 Jy/beam; contour levels are −1, 1, 2, ..., 512 times 8.3 mJy/beam; beamFWHM is 0.5× 0.4 mas at a position angle of 23◦.5. Jet Transverse StructureThe high-resolution 1.6 GHz images allow the transverse structure of the jet tobe resolved from about 10 to 20 mas from the core. While some cuts show thesignature of limb-brightening, overall the brightness maximum is statistically nomore likely to occur at the edge or in the center, suggesting a more complexbrightness distribution than the simplest inner-spine–outer-sheath models. Asample of transverse cuts is shown in Figure 2. Full details will be presentedelsewhere.Acknowledgments. We gratefully acknowledge the VSOP Project, whichis led by the Japanese Institute of Space and Astronautical Science in coopera-tion with many organizations and radio telescopes around the world.216 Pant et al.Figure 2. Transverse cuts across the jet made in the 1.6 GHz VSOP imageof 3C279 from 2000 Apr 1, showing the variety of profiles observed.Referencesde Pater, I., & Perley, R. A. 1983, ApJ, 273, 64Edwards, P. G., Hirabayashi, H., Lovell, J. E. J., Piner, B. G., Unwin, S. C., & Wehrle,A. E. 1999, Astronomische Nachrichten, 320, 230Hirabayashi, H., et al. 2000a, Astrophysical Phenomena Revealed by Space VLBI, Eds.H. Hirabayashi, P.G. Edwards, and D.W. Murphy, (ISAS, Japan), p. 25Hirabayashi, H., et al. 2000b, Advances in Space Research, 26, 689Homan, D. C., Lister, M. L., Kellermann, K. I., Cohen, M. H., Ros, E., Zensus, J. A.,Kadler, M., & Vermeulen, R. C. 2003, ApJ, 589, L9Jorstad, S. G., Marscher, A. P., Lister, M. L., Stirling, A. M., Cawthorne, T. V., Gómez,J.-L., & Gear, W. K. 2004, AJ, 127, 3115Lovell, J. 2000, Astrophysical Phenomena Revealed by Space VLBI, Eds.H. Hirabayashi, P.G. Edwards, and D.W. Murphy, (ISAS, Japan), p. 301Lovell, J. E. J., et al. 2004, ApJS, 155, 27Ojha, R., Homan, D. C., Roberts, D. H., et al. 2004, ApJS, 150, 187Piner, B. G., Edwards, P. G., Wehrle, A. E., Hirabayashi, H., Lovell, J. E. J., & Unwim,S. C. 2000a, AIP Conf. Series, 510, 308Piner, B. G., Edwards, P. G., Wehrle, A. E., et al. 2000b, ApJ, 537, 91Piner, B. G., Unwin, S. C., Wehrle, A. E., et al. 2003, ApJ, 588, 716Wehrle, A. E., et al. 1998, ApJ, 497, 178

A Complete Set of VSOP Observations of 3C279

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A Complete Set of VSOP Observations of 3C279

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