Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...186.1103d&link_type=abstract
American Astronomical Society, 186th AAS Meeting, #11.03; Bulletin of the American Astronomical Society, Vol. 27, p.827
Astronomy and Astrophysics
Astronomy
Scientific paper
We have used the VLBA to observe the nucleus of NGC 1275 at 15 and 43 GHz with angular resolution of 1.0 and 0.3 milliarcsec, respectively. Our observations reveal a bright core and two-sided, more extended structure. The peak intensity of the more prominent, southward-extending jet is located at a distance from the core consistent with apparent subluminal motion at 0.58 c (for H_0 = 50 km s(-1) Mpc(-1) ), continuing since this velocity was first measured (J. D. Romney, W. Alef, I. I. K. Pauliny-Toth, E. Preuss, & K. I. Kellermann 1982, in I. A. U. Symposium No. 97: Extragalactic Radio Sources, p. 291) from primitive maps made in 1979-81. The northward ``counter-jet'' extension is well detected at 15 GHz, with intensity relative to the core intermediate between the two observations at 8.4 GHz (R. C. Walker, J. D. Romney, & J. M. Benson 1994, ApJ, 430, L45) and at 22 GHz (R. C. Vermeulen, A. C. S. Readhead, & D. C. Backer 1994, ApJ, 430, L41) in which this feature was first discovered. In our observations at 43 GHz, the counter-jet is detected, but barely so. Both results are consistent with the model proposed by Vermeulen, Readhead, and Backer, in which the inverted spectrum of this component is a result of free-free absorption in a toroidal or disk-like region. Our 43-GHz observations resolve the core into two bright components separated by about 0.5 milliarcsec in a position angle close to the -9 degrees seen at 10-milliarcsec and indeed at much larger angular scales. A more diffuse structure extends about 1.1 milliarcsec at 45 degrees position angle from the more southerly of the two bright components, and then bends back to the original orientation. This structure is quite different from that seen previously at this frequency. Indications of large position-angle changes in the core on timescales of perhaps six months can be seen in our previous maps at 15, 10.7, and at 8.4 GHz as well.
Dhawan Vivek
Kellermann Kenneth I.
Romney Jonathan D.
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