measuring magnetic power spectra

of Hydra A

Petr Kuchar, Torsten Ensslin

Hydra A

optical x-ray

NASA/CXC/SAOLa Palma/B. McNamara

Hydra A

radio RM map

Greg Taylor, NRAO pacerman algorithm Dolag & Vogt & Ensslin

we measure this

rotation measure

we want that

previous works

• Laing 2008compare observed and computedstructure function

• Vogt & Ensslin 2005Bayesian

Bayesian approach

given RM data d

wanted power spectrum p

P(p|d)~P(d|p)P(p)

Likelihood

Jeffrey's Prior

correlation matrix

C

electron densitymagnetic density

cavity geometryprojection angle of jet

powerspectrum

maximize the posterior P(p|d)

analytical expressions for gradient and hessian

power spectrum

spectral index

projection angle

characteristics ofmagnetic field

• magnetic density:

• autocorrelation lengths

• spectral index

conclusion• maximum a posteriori method to retrieve

magnetic power spectra

• re-analysis of Hydra A data (as Vogt & Ensslin) now including cavities, noise, Galactic foreground, beam discussion, increased internal accuracy

• robust results: peaked spectrum with 3 kpc correlation length, indication of power-law inertia range on smaller scales

• required: better understanding of RM noise & beam effects, window effects on large scales