Constraints on the Accretion Region in NGC 1275 from VLBA Observations of the Counterjet

  • R. C. Walker
  • J. D. Romney
  • R. C. Vermeulen
  • V. Dhawan
  • K. I. Kellermann
Conference paper
Part of the International Astronomical Union book series (IAUS, volume 175)

Abstract

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).

Keywords

Spectral Index Accretion Disk Radial Dependence Hubble Constant Extragalactic Radio Source 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Levinson, A., Laor, A., and Vermeulen, R. C. (1995) Ap.J., 448, 589.ADSCrossRefGoogle Scholar
  2. Romney, J.D. et al. (1995) This Volume.Google Scholar
  3. Vermeulen, R.C., Readhead, A.C.S., and Backer, D.C. (1994), Ap.J., 430, L41.ADSCrossRefGoogle Scholar
  4. Walker, R.C., Romney, J.D., and Benson, J.M. (1994) Ap. J., 430, L45ADSCrossRefGoogle Scholar

Copyright information

© International Astronomical Union 1996

Authors and Affiliations

  • R. C. Walker
    • 1
  • J. D. Romney
    • 1
  • R. C. Vermeulen
    • 2
  • V. Dhawan
    • 1
  • K. I. Kellermann
    • 3
  1. 1.N.R.A.OSocorroUSA
  2. 2.CaltechPasadenaUSA
  3. 3.N.R.A.OCharlottesvilleUSA

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