superluminal_expansion_of_3c

SUPERLUMINAL EXPANSION OF 3C 273 

T.J. Pearson, S.C  Unwin, M.H. Cohen, R.P. Linfield, 

A.CS,

 Readhead, G.A. Seielstad, R.S. Simon, and R.C. Walker 

Owens Valley Radio Observatory 

California Institute of Technology 

Figure 1 shows hybrid maps of the core of 3C 273B at five epochs,  made  

with  arrays  of  4  or 5 VLBI antennas.  The maps span a period of  3.5  

years.

  They all show a bright  eastern  peak  and  a  lower-brightness  

extension  to  the  west.   There  is  a  local  maximum  in the western 

extension between 6 and 8 milliarcsec from the main peak.  This  ''blob

11

moves steadily further away from the main peak along a roughly  straight  

line in PA -116° ± 2°.  Compare this with the  position  angle  of  the  

25-arcsec  optical jet,

 -137°.

  The maps  show a slight curvature to the 

south with increasing  separation from the main peak.   Lower-resolution   

VLBI  maps  at  lower frequencies show that this curvature continues at 

greater  separations,  suggesting  a  smooth  connection  between   the   

milli-arcsecond  position  angle  and the position angle of the optical 

jet.

  In our latest map  (1981.09) the blob  is no longer detectable with 

the limited dynamic range of the VLBI network  (about

  20:1).  

The separation of the western blob from  the eastern peak increased 

steadily  between  1977  and 1980, with no evidence for acceleration or 

deceleration.  The  angular  expansion  rate  is  0.76  ±  0.04  milli-

arcsec/year,  corresponding  to a linear expansion rate of v/c = (5.3 ± 

0.3)/h,

 assuming z = 0.158, H

0

   =  100b  km/(s Mpc),  and  q

0

   =  0.05;  

1 milliarcsec = 6.0/h  l.y. = 1.9/h pc. 

In the  relativistic  jet  model  the  expansion  is  presumed  to  

represent  a  physical motion almost directly towards the observer;  we  

are  looking down a jet  of  relativistic  material  expelled  from  the  

quasar.

   The  eastern end of 3C 273B  is the "core", the point at which 

the jet becomes optically thick.  In a steady flow, this point  remains  

fixed  even  though  the  radiating  material has a high velocity.  The  

moving  (western) component  is a "knot" propagating outwards  along  the  

jet.

   In  order  to  account  for an apparent  transverse velocity v as 

large as 5.3c, the angle

<f>

 between the jet and the line of  sight  must  

be  small.  For h=l,  <|> must be  less than 21°, and the space velocity  is  

minimized  at

<j>

 = 11°

.

  These angles will be smaller for smaller  values  

of  h.   The probability  that  <\> should be as small as 11°  in a randomly 

selected quasar  is 1%, or 2% if the jet  is two-sided. 

355

S. Heeschen and C M.

Wade

(eds.),

Extragalactic Radio Sources,

355-356.

https://www.cambridge.org/core/terms

https://doi.org/10.1017/S0074180900028126

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356

T.

J.

 PI-ARSON

 ET AL. 

I

3C 273

10.65GHz

3C 273  is far from being a  randomly  

chosen  quasar:  it is the closest quasar 

in the 3CR sample and  has  an  intrinsic  

optical   intensity  about  4  times  the  

intensity  of the  other  quasars  in  the  

sample.

   It is surprising  that  it should 

also  be  exceptional  in  having  a  jet  

pointing   almost   directly  at  us.   A   

possible explanation  is that the  optical  

radiation,   like   the   radio,  is  not  

isotropic.  There is no  direct  evidence  

for

  this,

  but  beaming  of  the optical 

continuum  cannot be ruled  out.   If  the  

optical  radiation  is isotropic, then the 

small angle between the radio jet and the 

line  of  sight causes grave difficulties 

for  the  simple  relativistic  theories.  

For  example,  if the difference in radio 

intensity between optically selected  and  

radio-selected  quasars  is  due  to  the  

relativistic   beaming   of   the   radio   

radiation, because radio-selected  quasars  

point towards us, we would expect to  see  

50   to   100   radio-quiet   quasars  of  

comparable optical magnitude  to  3C 273, 

which we do not. 

This work was supported by the  NSF  (AST  

79-13249). 

REFERENCE 

Pearson, T.J., Unwin, S.C., Cohen,  M.H.,  

Linfield,  R.P.,  Readhead,

  A.C.S.,  

Seielstad, G.A.,  Simon,  R.S.,  and  

Walker,

  R.C.:   1981,  Nature, 290, 

pp.

 365-368. 

Figure 1. 

Maps of 3C 273B at 10.65 GHz at five 

epochs,

  from Pearson et al.

 (1981), 

who    give    details    of     the     

observations.   Contour  levels  and  

restoring beam are the same for  all  

maps.

   (Reproduced by permission of 

Macmillan Journals Ltd.) 