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1
Striking New Evidence for the Action of a
Cosmic Battery in AGN Denise Gabuzda (University
College Cork)
Dimitris Christodoulou (University of
Massachusetts Lowell) Ioannis
Contopoulos (Academy of Athens)
Demosthenes Kazanas (NASA/Goddard)
(3) Parsec scales Transverse FR gradients are
observed across a number of AGN jets on parsec
(VLBI) scales. Two examples (black star is centre
of activity, arrow shows direction of gradient)
Meier, Koide Uchida 2001
(1) Faraday rotation (FR) and helical/toroidal
fields Rotation of central supermassive black
hole and accretion disc jet outflow gives rise
to helical jet B field. Yields FR gradient
across the jet due to systematically changing
line-of-sight B
CCW
CW
?
Reichstein Gabuzda 2010
LOS B away from observer (RM lt 0)
B
Contopoulos et al. (2009) found an excess of CW
gradients. For FR gradients detected relatively
close to VLBI core 21 CW, 7 CCW
Prob of 21 or more being CW by chance
0.6
Jet axis
LOS B towards observer (RM gt 0)
(4) Kiloparsec scales Examination of 85 published
FR maps by Christodoulou et al. (2011) yielded
firm transverse RM gradients in 7 sources,
tentative gradients in 4 more. 9 of these 11 have
CCW gradients! Two examples

• (2) The PoyntingRobertson Battery (Contopoulos
  et al. 2009 refs therein)
• ? Radiation absorbed by charges in rotating
  accretion disc is re-radiated isotropically in
  rest frame, beamed in direction of motion
  (rotation) in observers frame
• Charges thus feel a reaction force
• Deceleration of e gtgt deceleration of p due to
  dependence on mass (Thomson cross section m-2)
• Electric current in direction of rotation
• Couples direction of rotation and poloidal B
  field wound up by differential rotation
• Azimuthal and poloidal B fields ae coupled

Eilek Owen 2002
CCW
CCW
Bonafede et al. 2010

• With 4 firm decaparsec-scale transverse FR
  gradients (right), have 13/15 CCW
• Prob of 13 or more of 15 being CCW by chance
  0.4
• Predominance of CW/CCW gradients on pc/kpc scales!

Croke et al. 2010
Integration path passes through both regions of
helical field Direction of FR gradient depends on
which region dominates FR integral
If field emerges in inner disc and closes in
outer disc, gives nested helix structure
CCW

• (5) Conclusion
• Excess of CW/CCW transverse FR gradients across
  AGN jets on smaller/larger scales, requires
  coupling between poloidal and azimuthal jet B
  fields mechanism must also explain reversal from
  CW to CCW.
• The PoyntingRobertson battery can provide this!
• Currents must be involved any other ideas??

FR gradient for inner/ outer helical fields are
always CW/CCW on sky
B fields RM gradients
When rotation is reversed, direction of seed
poloidal B field is too azimuthal B field
remains unchanged
Asada et al. 2002, PASJ, 54, L39 Bonafede et al.
2010, AA, 513, 30 Christodoulou et al. 2011,
ApJ, submitted Contopoulos et al. 2009, ApJ,
702, L148 Croke et al. 2010, MNRAS, 402, 259
Eilek Owen 2002, ApJ, 567, 202 Mahmud 2009,
PhD Thesis, Physics, UCC Meier et al. 2001,
Science, 291, 84 Reichstein Gabuzda 2011, in
prep
Contopoulos et al. 2009
Mahmud 2010
Mahmud 2010