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Constraints on the accretion region in NGC 1275 from VLBA observations of the counterjet

Published online by Cambridge University Press:  25 May 2016

R.C. Walker ,
J.D. Romney ,
R.C. Vermeulen ,
V. Dhawan  and
K.I. Kellermann
R.C. Walker
Affiliation:
1 N.R.A.O. - Socorro, NM, USA
J.D. Romney
Affiliation:
1 N.R.A.O. - Socorro, NM, USA
R.C. Vermeulen
Affiliation:
2 Caltech - Pasadena, CA, USA
V. Dhawan
Affiliation:
1 N.R.A.O. - Socorro, NM, USA
K.I. Kellermann
Affiliation:
3 N.R.A.O. - Charlottesville, VA, USA

Extract

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A northern feature, that is most likely related to a counterjet, was found on parsec scales in 3C 84 (which is in NGC 1275) in “First Science” observations on the VLBA1 at 8.4 GHz (Walker et al., 1994) and in Global VLBI observations at 22 GHz (Vermeulen et al., 1994). The jet/counterjet length ratio, brightness ratio at 22 GHz, and speeds, as measured over many years with VLBI, fit a simple beaming model with symmetric jets oriented at 30–50 degrees to the line-of-sight and traveling at a speed of 0.3–0.5 times the speed of light. These ranges allow for Hubble constants of between 50 and 100 km s–1 Mpc–1. The brightness of the counterjet at 8.4 GHz was very much lower than expected with this model, assuming that the spectral indices in the near and far side jets are similar. This was interpreted as the result of free-free absorption in an ionized medium that lies in front of the counterjet but not in front of the near-side jet. An accretion disk or torus has an appropriate geometry to show this effect (for an analysis, see Levinson et al., 1995).

Type
Properties of Radio Sources
Information
Symposium - International Astronomical Union , Volume 175: Extragalactic Radio Sources , 1996 , pp. 30 - 32
Copyright
Copyright © Kluwer 1996 

References

Levinson, A., Laor, A., and Vermeulen, R. C. (1995) Ap. J. , 448, 589.CrossRefGoogle Scholar
Romney, J.D. et al. (1995) This Volume. Google Scholar
Vermeulen, R.C., Readhead, A.C.S., and Backer, D.C. (1994), Ap. J. , 430, L41.Google Scholar
Walker, R.C., Romney, J.D., and Benson, J.M. (1994) Ap. J. , 430, L45.Google Scholar