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The first space VLBI image of 3C279
Adv. Space Res. Vol. 26, No. 4, pp. 68%92,2000 8 2000 COSPAR. Published by Elsevier Science Ltd. AII rights reserved Printed in Great Britain 0273-1177KlO $20.00 + 0.00 PII: sO273-1177(99p1192-8
Pergamon www.elsevier.nl/hcatehsr
THE FIRST
SPACE
VLBI IMAGE
OF 3C279
H. Hirabayashil, P.G. Edwards’, A.E. Wehrlez, SC. Unwin3, B.G. Piner3, J.E. J. Lovelll, H. Kobayashi’, R. Okayasul, F. Makinoi, T. Kii’, and E. Valtaoja4 1 ISAS, Sagamihara, Kanagawa 229-8510, Japan 2 IPAC/JPL/Caltech, Pasadena, California, USA 3 JPL, Pasadena, California, USA 4 Helsinki U. of Technology, Finland
ABSTRACT The first 5 GHz VSOP (VLBI Space Observatory Programme) observation of the quasar 3C279 was conducted on 10 January 1998 with the satellite HALCA and an array of ground radio telescopes. The high dynamic range image presented here reveals that the core and the secondary component ~3 milli-arcseconds from the core dominate the compact radio emission, but that lower level features at intermediate distances from the core are also evident. 0 2000 COSPAR. Published by Elsevier Science Ltd.
INTRODUCTION The quasar 3C279 was the first for which apparent superluminal motion was detected (Whitney et al. 1971). Monitoring of 3C279 has enabled several components to be tracked as they have moved away from the core. The speeds and position angles have differed from component to component. VLA images reveal components ranging from 95 milli-arcseconds to 4.7 arcseconds from the core along approximately the same position angle as the milli-arcsecond-scale components (de Pater and Perley, 1983). The speeds and position angles of the VLBI components have been interpreted as being due to precession of a constant speed jet (Abraham and Carrara, 1998). A precession period (in the observer’s frame) of 22 years has been inferred from the motions of four jet components, and further observations will enable the validity of this model to be examined. Since 1987,3C279 has been in a very active phase with several multi-frequency outbursts having been detected. During multi-wavelength monitoring in January/February 1996, 3C279 obligingly reached its highest recorded level in >lOO MeV gamma rays, and also showed an increase by a factor of 2.6 over -8 hours (Wehrle et al., 1998).
OBSERVATION
AND DATA REDUCTION
The VLBI Space Observatory Programme is described elsewhere (e.g. Hirabayashi and Hirosawa, 1998). VSOP observations of 3C279 were made on 1998 January 9 at 1.6 GHz and on 1998 January 10
689
690
H. Hirabayashi et al.
at 5 GHz and we report on the latter of these observations here. Data from HALCA, via the Madrid and Goldstone tracking stations, nine elements of the NRA0 VLBA (a power outage prevented Hancock from participating) and the Usuda (Japan) 64 m telescope were correlated at Socorro. The Goldstone tracking station had undergone an upgrade of its software and hardware, notably the frame synchronization circuit in the telemetry decoder, in early December 1997, and the tracking pass in this observation proceeded smoothly. The corresponding upgrade of the Madrid tracking station did not take place until 1998 January 17, and the Madrid tracking pass was affected by a number of ‘delay glitches’ of typically -125 nanoseconds, which were identified and treated prior to fringe-fitting the data in AIPS. The Usuda 64 m joined late in the 10 hr observation, by which time the source had set at all VLBA sites except Mauna Kea, and so this data has been excluded in this analysis. 3c279
at
4.808
GHz
1998
Jan
10
I”“““““““““‘1
t,
I
0
(III
b
I
,I.,
100 Radial
III.1
.
200 UV
distance
along
P.A.
.
..i
300 65O
(1 O6 X)
Fig. 1. Correlated flux density at 5 GHz plotted against projected of -115” (using the final edited and calibrated data set).
(u, v) distance for a position angle
Imaging was carried out using the Caltech Difmap package (Shepherd, 1997). Inspection of the data indicated that the nominal gain calibration for Saint Croix was in error by >30%, so a groundonly image was first made using the other 8 elements of the VLBA. Once amplitude self-calibration had been carried out for these, Saint Croix was added, and after a satisfactory ground-only image had been generated this was used as a starting model for the full VSOP data-set. The amplitude calibration information for HALCA proved to be accurate to better than 5%. A plot of the correlated flux against (u, v)-distance is shown in Figure 1, where all (u, v) distances have been projected to a position angle of -115”. The continental USA and Saint Croix baselines provide projected (u, v) distances up to 80 MX, with the North Liberty-Mauna Kea baseline extending this to 100MX and Saint Croix-Mauna Kea providing a further extension to 120MX. The addition of HALCA enables projected baselines from 60MX out to 340MX to be sampled, with a resulting improvement in resolution along the jet direction by a factor of 2.8, demonstrating the utility of space VLBI observations. The beating evident in the correlated flux clearly indicates that on milliarcsecond scales the 5 GHz morphology is dominated by two components of similar flux density.
Space VLBI Image of 3C279
691
DISCUSSION The resulting image is shown in Figure 2. As implied by Figure 1, the second component (on the right) lies at a position angle of of -115”, and at a distance of -3 milli-arcseconds from the core. We identify the second component with the component C4 of Unwin et al. (1989) and Carrara et al. (1993), as the position angle of -115” is consistent with these earlier observations. For this identification to be correct, however, C4 must have accelerated from the 0.15f0.01 mas/yr determined by Carrara et aL (1993) from observations between 1985.5 and 1990.5. Indeed, observations since 1991.0 at 22 GHz (Wehrle et al., 1996) and the 15 GHz VLBA snap-shot observations of Kellermann suggest an apparent motion for this et al. (1998) (see also http:// www. cv. nrao. edu/2cmsurvey/) component of N0.19mas/yr, although an extrapolation of this motion does not connect smoothly with the motion for C4 determined by Carrara et al. (1993) : taking these data at face value, a rapid change of apparent speed between early 1990 and mid-1991 is implied.
J 6
4
2 Right
0 Ascension
-2
-4
-6
(mos)
Fig. 2. VSOP image of 36279 at 5GH.z at epoch 1998.03. Contours are at -1, 1, 2, 4, 8, 16, 32, 64, 128 and 256 times 0.012 Jy/beam, with a peak brightness 3.98 Jy/beam. The beam is 1.82masx 0.237mas (FWHM) at a position angle of 27.7’. It is notable that the leading edge of the second component is much sharper than the trailing edge, suggesting that this represents the “working surface” or shock front. Combination of this data with that of the previous day’s 1.6 GHz VSOP observation will enable the spectral index variation in this region to be studied. Inspection of Figure 2 also clearly reveals an extension to the core at a position angle of approximately This is probably related to the stationary feature about 1 mas from the core noted by -130”. Leppanen et al. (1995) and Wehrle et al. (1996). This feature appears to be associated with a
692
H. Hirabayashiet al.
change in the magnetic field direction (Lepplnen et al., 1995).
from being perpendicular
to the jet to being longitudinal
Figure 2 has a dynamic range of mlOOO:l, demonstrating that the addition of HALCA’s small orbiting telescope to a ground array can produce images of high resolution and high quality. The precession of HALCA’s orbit results in the best angular resolution along the jet direction around April 1999, and VSOP observations at this time will enable the evolution and motion of the jet components to be monitored in more detail.
ACKNOWLEDGMENTS We gratefully Astronautical
acknowledge the VSOP Project, which is led by the Japanese Institute of Space and Science in cooperation with many organizations and radio telescopes around the world.
REFERENCES
Abraham, Carrara,
Z., and E.A. Carrara,
The Precessing
Jet in 3C 279, Astrophys.
J., 496, 172 (1998).
E.A., Z. Abraham, S.C. Unwin and J.A. Zensus, The milliarcsecond 3C279, Astron. & Astrophys., 279, 83 (1993).
de Pater, I., and R.A. Perley, The Radio Structure
of 3C279, Astrophys.
Hirabayashi, H., and H. Hirosawa, VSOP Mission, General Introduction Space. Res. this volume (1998).
structure
of the quasar
J., 273, 64 (1983). and Current Overview, Ah.
Kellermann, K.I., R.C. Vermeulen, J.A. Zensus and M.H. Cohen, Sub-Milliarcsecond Quasars and Active Galactic Nuclei Ash-on. J., 115, 1295 (1998).
Imaging of
Leppanen, K.J., J.A. Zensus and P.J. Diamond, Linear Polarization Imaging with Very Long Baseline Interferometry at High Frequencies, A&on. J., 110, 2479 (1995). Shepherd, M.C., Difmap: An Interactive Program for Synthesis Imaging, in AstronomicaZ Data Analysis Software and Systems VIeds. G. Hunt and H.E. Payne, ASP Conference Series 125, 77 (1997). Unwin, SC., M.H. Cohen, J.A. Biretta, M.W. Hodges and J.A. Zensus, Superluminal Quasar 3C279, Astrophys. J., 340, 117 (1989). *
Motion in the
Wehrle, A.E., S.C. Unwin, A.C. Zook, C.M. Urry, A.P. Marscher and H. Terasranta, VLBI Imaging and Multiwavelength Variability of 3C 279, in Blazur Continzlzlm Variability, eds. H.R. Miller, J.R. Webb, and J.C. Noble, ASP Conference Series 110, 430 (1996). Wehrle, A.E., E. Pian, C.M. Urry, L. Maraschi, I.M. McHardy et al., Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279, Astrophys. J., 497, 178 (1998). Whitney, A.R., 1.1. Shapiro, A.E.E. Rogers, D.S. Robertson, C.A. Knight et al., Quasars Revisited: Rapid Time Variations Observed Via Very-Long-Baseline Interferometry, Science, 173, 225 (1971).
Pergamon www.elsevier.nl/hcatehsr
THE FIRST
SPACE
VLBI IMAGE
OF 3C279
H. Hirabayashil, P.G. Edwards’, A.E. Wehrlez, SC. Unwin3, B.G. Piner3, J.E. J. Lovelll, H. Kobayashi’, R. Okayasul, F. Makinoi, T. Kii’, and E. Valtaoja4 1 ISAS, Sagamihara, Kanagawa 229-8510, Japan 2 IPAC/JPL/Caltech, Pasadena, California, USA 3 JPL, Pasadena, California, USA 4 Helsinki U. of Technology, Finland
ABSTRACT The first 5 GHz VSOP (VLBI Space Observatory Programme) observation of the quasar 3C279 was conducted on 10 January 1998 with the satellite HALCA and an array of ground radio telescopes. The high dynamic range image presented here reveals that the core and the secondary component ~3 milli-arcseconds from the core dominate the compact radio emission, but that lower level features at intermediate distances from the core are also evident. 0 2000 COSPAR. Published by Elsevier Science Ltd.
INTRODUCTION The quasar 3C279 was the first for which apparent superluminal motion was detected (Whitney et al. 1971). Monitoring of 3C279 has enabled several components to be tracked as they have moved away from the core. The speeds and position angles have differed from component to component. VLA images reveal components ranging from 95 milli-arcseconds to 4.7 arcseconds from the core along approximately the same position angle as the milli-arcsecond-scale components (de Pater and Perley, 1983). The speeds and position angles of the VLBI components have been interpreted as being due to precession of a constant speed jet (Abraham and Carrara, 1998). A precession period (in the observer’s frame) of 22 years has been inferred from the motions of four jet components, and further observations will enable the validity of this model to be examined. Since 1987,3C279 has been in a very active phase with several multi-frequency outbursts having been detected. During multi-wavelength monitoring in January/February 1996, 3C279 obligingly reached its highest recorded level in >lOO MeV gamma rays, and also showed an increase by a factor of 2.6 over -8 hours (Wehrle et al., 1998).
OBSERVATION
AND DATA REDUCTION
The VLBI Space Observatory Programme is described elsewhere (e.g. Hirabayashi and Hirosawa, 1998). VSOP observations of 3C279 were made on 1998 January 9 at 1.6 GHz and on 1998 January 10
689
690
H. Hirabayashi et al.
at 5 GHz and we report on the latter of these observations here. Data from HALCA, via the Madrid and Goldstone tracking stations, nine elements of the NRA0 VLBA (a power outage prevented Hancock from participating) and the Usuda (Japan) 64 m telescope were correlated at Socorro. The Goldstone tracking station had undergone an upgrade of its software and hardware, notably the frame synchronization circuit in the telemetry decoder, in early December 1997, and the tracking pass in this observation proceeded smoothly. The corresponding upgrade of the Madrid tracking station did not take place until 1998 January 17, and the Madrid tracking pass was affected by a number of ‘delay glitches’ of typically -125 nanoseconds, which were identified and treated prior to fringe-fitting the data in AIPS. The Usuda 64 m joined late in the 10 hr observation, by which time the source had set at all VLBA sites except Mauna Kea, and so this data has been excluded in this analysis. 3c279
at
4.808
GHz
1998
Jan
10
I”“““““““““‘1
t,
I
0
(III
b
I
,I.,
100 Radial
III.1
.
200 UV
distance
along
P.A.
.
..i
300 65O
(1 O6 X)
Fig. 1. Correlated flux density at 5 GHz plotted against projected of -115” (using the final edited and calibrated data set).
(u, v) distance for a position angle
Imaging was carried out using the Caltech Difmap package (Shepherd, 1997). Inspection of the data indicated that the nominal gain calibration for Saint Croix was in error by >30%, so a groundonly image was first made using the other 8 elements of the VLBA. Once amplitude self-calibration had been carried out for these, Saint Croix was added, and after a satisfactory ground-only image had been generated this was used as a starting model for the full VSOP data-set. The amplitude calibration information for HALCA proved to be accurate to better than 5%. A plot of the correlated flux against (u, v)-distance is shown in Figure 1, where all (u, v) distances have been projected to a position angle of -115”. The continental USA and Saint Croix baselines provide projected (u, v) distances up to 80 MX, with the North Liberty-Mauna Kea baseline extending this to 100MX and Saint Croix-Mauna Kea providing a further extension to 120MX. The addition of HALCA enables projected baselines from 60MX out to 340MX to be sampled, with a resulting improvement in resolution along the jet direction by a factor of 2.8, demonstrating the utility of space VLBI observations. The beating evident in the correlated flux clearly indicates that on milliarcsecond scales the 5 GHz morphology is dominated by two components of similar flux density.
Space VLBI Image of 3C279
691
DISCUSSION The resulting image is shown in Figure 2. As implied by Figure 1, the second component (on the right) lies at a position angle of of -115”, and at a distance of -3 milli-arcseconds from the core. We identify the second component with the component C4 of Unwin et al. (1989) and Carrara et al. (1993), as the position angle of -115” is consistent with these earlier observations. For this identification to be correct, however, C4 must have accelerated from the 0.15f0.01 mas/yr determined by Carrara et aL (1993) from observations between 1985.5 and 1990.5. Indeed, observations since 1991.0 at 22 GHz (Wehrle et al., 1996) and the 15 GHz VLBA snap-shot observations of Kellermann suggest an apparent motion for this et al. (1998) (see also http:// www. cv. nrao. edu/2cmsurvey/) component of N0.19mas/yr, although an extrapolation of this motion does not connect smoothly with the motion for C4 determined by Carrara et al. (1993) : taking these data at face value, a rapid change of apparent speed between early 1990 and mid-1991 is implied.
J 6
4
2 Right
0 Ascension
-2
-4
-6
(mos)
Fig. 2. VSOP image of 36279 at 5GH.z at epoch 1998.03. Contours are at -1, 1, 2, 4, 8, 16, 32, 64, 128 and 256 times 0.012 Jy/beam, with a peak brightness 3.98 Jy/beam. The beam is 1.82masx 0.237mas (FWHM) at a position angle of 27.7’. It is notable that the leading edge of the second component is much sharper than the trailing edge, suggesting that this represents the “working surface” or shock front. Combination of this data with that of the previous day’s 1.6 GHz VSOP observation will enable the spectral index variation in this region to be studied. Inspection of Figure 2 also clearly reveals an extension to the core at a position angle of approximately This is probably related to the stationary feature about 1 mas from the core noted by -130”. Leppanen et al. (1995) and Wehrle et al. (1996). This feature appears to be associated with a
692
H. Hirabayashiet al.
change in the magnetic field direction (Lepplnen et al., 1995).
from being perpendicular
to the jet to being longitudinal
Figure 2 has a dynamic range of mlOOO:l, demonstrating that the addition of HALCA’s small orbiting telescope to a ground array can produce images of high resolution and high quality. The precession of HALCA’s orbit results in the best angular resolution along the jet direction around April 1999, and VSOP observations at this time will enable the evolution and motion of the jet components to be monitored in more detail.
ACKNOWLEDGMENTS We gratefully Astronautical
acknowledge the VSOP Project, which is led by the Japanese Institute of Space and Science in cooperation with many organizations and radio telescopes around the world.
REFERENCES
Abraham, Carrara,
Z., and E.A. Carrara,
The Precessing
Jet in 3C 279, Astrophys.
J., 496, 172 (1998).
E.A., Z. Abraham, S.C. Unwin and J.A. Zensus, The milliarcsecond 3C279, Astron. & Astrophys., 279, 83 (1993).
de Pater, I., and R.A. Perley, The Radio Structure
of 3C279, Astrophys.
Hirabayashi, H., and H. Hirosawa, VSOP Mission, General Introduction Space. Res. this volume (1998).
structure
of the quasar
J., 273, 64 (1983). and Current Overview, Ah.
Kellermann, K.I., R.C. Vermeulen, J.A. Zensus and M.H. Cohen, Sub-Milliarcsecond Quasars and Active Galactic Nuclei Ash-on. J., 115, 1295 (1998).
Imaging of
Leppanen, K.J., J.A. Zensus and P.J. Diamond, Linear Polarization Imaging with Very Long Baseline Interferometry at High Frequencies, A&on. J., 110, 2479 (1995). Shepherd, M.C., Difmap: An Interactive Program for Synthesis Imaging, in AstronomicaZ Data Analysis Software and Systems VIeds. G. Hunt and H.E. Payne, ASP Conference Series 125, 77 (1997). Unwin, SC., M.H. Cohen, J.A. Biretta, M.W. Hodges and J.A. Zensus, Superluminal Quasar 3C279, Astrophys. J., 340, 117 (1989). *
Motion in the
Wehrle, A.E., S.C. Unwin, A.C. Zook, C.M. Urry, A.P. Marscher and H. Terasranta, VLBI Imaging and Multiwavelength Variability of 3C 279, in Blazur Continzlzlm Variability, eds. H.R. Miller, J.R. Webb, and J.C. Noble, ASP Conference Series 110, 430 (1996). Wehrle, A.E., E. Pian, C.M. Urry, L. Maraschi, I.M. McHardy et al., Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279, Astrophys. J., 497, 178 (1998). Whitney, A.R., 1.1. Shapiro, A.E.E. Rogers, D.S. Robertson, C.A. Knight et al., Quasars Revisited: Rapid Time Variations Observed Via Very-Long-Baseline Interferometry, Science, 173, 225 (1971).