Alma Mater Studiorum Universit`a degli Studi di Bologna ... - Inaf

6.2. Two-dimensional analysis: rotation measure and depolarization 115
IMAGE: 0755.RM.4.0_BLANK.FITS
DECLINATION (J2000)
37 48 00
37 47 30
37 47 00
37 46 30
;20 ;10 0 10 20
RAD/M/M
07 58 36
07 58 32 07 58 28 07 58 24
RIGHT ASCENSION (J2000)
10 kpc
DECLINATION (J2000)
37 48 00
37 47 30
37 47 00
37 46 30
IMAGE: 0755.RM.1.3_BLANK.FITS
;20 ;10 0 10 20
RAD/M/M
07 58 36
07 58 32 07 58 28 07 58 24
RIGHT ASCENSION (J2000)
10 kpc
07 58 20
Figure 6.4: Images of the rotation measure for 0755+37, computed from weighted least-squares
fits to the position angle –λ 2 relation at frequencies of 1385.1, 1469.1 and 4860.1 MHz. The
angular resolutions are 4.0 arcsec FWHM (left) and 1.3 arcsec FWHM (right).
IMAGE: 0755_K;BURN_4ARCSEC_4SIGMAP.FITS
0 100 200 300 400
rad^2/m^4
IMAGE: 0755_K;BURN_1.3ARCSEC.FITS
0 100 200 300 400
rad^2/m^4
37 48 00
37 48 00
DECLINATION (J2000)
37 47 30
37 47 00
37 46 30
DECLINATION (J2000)
37 47 30
37 47 00
37 46 30
07 58 36
07 58 32 07 58 28 07 58 24
RIGHT ASCENSION (J2000)
07 58 36
07 58 32 07 58 28 07 58 24
RIGHT ASCENSION (J2000)
07 58 20
Figure 6.5: Images of Burn law k for 0755+37 computed from weighted least-squares fits to the
relation p(λ)= p(0)exp(−kλ 4 ) at frequencies of 1385.1, 1469.1 and 4860.1 MHz. The angular
resolutions are 4.0 arcsec FWHM (left) and 1.3 arcsec FWHM (right).
This scenario is confirmed by the profiles of〈k〉 across the source (Fig. 6.6): at lower resolution
the profile is asymmetrical, with less depolarization at a given distance from the core in the E lobe
and a peak which is displaced slightly W of the nucleus. In contrast, the〈k〉 profile at 1.3 arcsec
resolution is symmetrical and lies significantly below that at 4.0 arcsec.
The high k values in the W lobe at the lower resolution are mostly seen in a cone-like structure
(Fig. 6.5 left), as was already pointed out by Bondi et al. (2000). It is possible that the origin of
such structure may be gas and field compression or the development of a mixing layer as discussed
for M 84 and 3C 270 (Sec. 5.8.5). To confirm this picture, higher resolution X-ray observations are
needed. In contrast, a region with very low and almost constant depolarization is observed at the
leading edge of the W lobe, beyond the end of the approaching jet.
115