Properties of the warm magnetized ISM, as inferred from WSRT polarimetric imaging

Haverkorn, M.; Katgert, P.; Bruyn, A. G. de

doi:10.1051/0004-6361:200400042

Cited by 26 publications

(25 citation statements)

References 33 publications

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“…As discussed in Haverkorn et al (2004), the random magnetic field has a correlation length of order 10 parsec. Shortly we will estimate that the length of the line of sight through ionized regions in the direction of GEMINI is of the order of 130 parsec.…”

Section: The Line-of-sight Component Of the Large-scale Magnetic Fieldmentioning

confidence: 97%

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WSRT Faraday tomography of the Galactic ISM at λ ~ 0.86 m

Schnitzeler

Katgert

Bruyn

2008

A&A

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Aims. We investigate the properties of the Galactic ISM by applying Faraday tomography to a radio polarization data set in the direction of the Galactic anti-centre. Methods. We address the problem of missing large-scale structure in our data, and show that this does not play an important role for the results we present. Results. The main peak of the Faraday depth spectra in our data set is not measurably resolved for about 8% of the lines of sight. An unresolved peak indicates a separation between the regions with Faraday rotation and synchrotron emission. However, cosmic rays pervade the ISM, and synchrotron emission would therefore also be produced where there is Faraday rotation. We suggest that the orientation of the magnetic field can separate the two effects. By modelling the thermal electron contribution to the Faraday depth, we map the strength of the magnetic field component along the line of sight. Polarized point sources in our data set have rotation measures that are comparable to the Faraday depths of the diffuse emission in our data. Our Faraday depth maps show narrow canals of low polarized intensity. We conclude that depolarization over the telescope beam produces at least some of these canals. Finally, we investigate the properties of one conspicuous region in this data set and argue that it is created by a decrease in line-of-sight depolarization compared to its surroundings.

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Section: The Line-of-sight Component Of the Large-scale Magnetic Fieldmentioning

confidence: 97%

“…Since the 1990s interferometric studies at low frequencies have led to new insights in e.g. the properties of the ISM on small scales, and on turbulence in the Galactic ISM (Wieringa et al 1993;Haverkorn et al 2004Haverkorn et al , 2006.…”

Section: Introductionmentioning

confidence: 99%

WSRT Faraday tomography of the Galactic ISM at λ ~ 0.86 m

Schnitzeler

Katgert

Bruyn

2008

A&A

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“…The scales of turbulent fluctuations in the interstellar magnetic field have been investigated more recently by Marijke Haverkorn and colleagues, again using the technique of Faraday rotation (Haverkorn et al, 2004b(Haverkorn et al, ,a, 2006. Haverkorn and her group have utilized both measurements of polarization of the galactic nonthermal radiation (Haverkorn et al, 2004b,a) as well as Faraday rotation of extragalactic sources (Haverkorn et al, 2006).…”

Section: Discussionmentioning

confidence: 99%

Observational tests of the properties of turbulence in the Very Local Interstellar Medium

Spangler

Savage

Redfield

2010

Nonlin. Processes Geophys.

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Abstract. The Very Local Interstellar Medium (VLISM) contains clouds which consist of partially-ionized plasma. These clouds can be effectively diagnosed via high resolution optical and ultraviolet spectroscopy of the absorption lines they form in the spectra of nearby stars. Information provided by these spectroscopic measurements includes values for ξ , the root-mean-square velocity fluctuation due to turbulence in these clouds, and T , the ion temperature, which may be partially determined by dissipation of turbulence. We consider whether this turbulence resembles the extensively studied and well-diagnosed turbulence in the solar wind and solar corona. Published observations are used to determine if the velocity fluctuations are primarily transverse to a largescale magnetic field, whether the temperature perpendicular to the large scale field is larger than that parallel to the field, and whether ions with larger Larmor radii have higher temperatures than smaller gyroradius ions. We ask if the spectroscopically-deduced parameters such as ξ and T depend on the direction on the sky. We also consider the degree to which a single temperature T and turbulence parameter ξ account for the spectral line widths of ions with a wide range of masses. A preliminary examination of the published data shows no evidence for anisotropy of the velocity fluctuations or temperature, nor Larmor radius-dependent heating. These results indicate differences between solar wind and Local Cloud turbulence. Possible physical reasons for these differences are discussed.

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“…A plot of RM vs. S x 1/2 (Figure 2) shows that there is no clear correlation between RM and S x 1/2 in the remnant, which means that the RMs originate from the ISM/halo along the line-of-sight. Therefore the RM variations across the remnant may reflect the structure of the magnetised interstellar medium (Haverkorn et al 2004) and the smooth component may tell us about the overall magnetic field morphology within the remnant (Ransom et al 2008). This will form the basis of our further analysis of these data.…”

Section: Determination Of N E and B ||mentioning

confidence: 99%

Spectropolarimetry of supernova remnant G296.5 + 10.0

Harvey-Smith¹,

Gaensler²,

Ng³

et al. 2008

Proc. IAU

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Abstract. Radio continuum emission from the supernova remnant G296.5 + 10.0 was observed using the Australia Telescope Compact Array. Using a 104 MHz bandwidth split into 13 × 8 MHz spectral channels, it was possible to produce a pixel-by-pixel image of Rotation Measure (RM) across the entire remnant. A lack of correlation between RM and X-ray surface brightness reveals that the RMs originate from outside the remnant. Using this information, we will characterise the smooth component of the magnetic field within the supernova remnant and attempt to probe the magneto-ionic structure and turbulent scale sizes in the ISM and galactic halo along the line-of-sight.Keywords. Polarization -magnetic fields -ISM: supernova remnants -ISM: radio continuum -X-rays: ISM ObservationsThe supernova remnant G296.5 + 10.0 was observed using the Australia Telescope Compact Array at 1.4 GHz with an angular resolution of 30 arcseconds. Signals from the dual linear polarized feeds were combined to produce images of the remnant in linear polarisation. The Rotation Measure synthesis method (Brentjens & de Bruyn, 2005) was employed to obtain an RM spectrum at each pixel in the image (Figure 1). The 104 MHz bandwidth was split into 13 × 8 MHz spectral channels, giving sufficient coverage in λ 2 to remove any nπ ambiguities in the RM values. X-ray data in the energy range 0.1-2.4 keV were taken from the ROSAT archive, via NASA's SkyView. These complimentary data allow us to estimate the electron density in the remnant. Determination of n e and B ||In order to disentangle the electron density (n e ) and line-of-sight magnetic field (B || ) we measured the X-ray intensity at every point in the ROSAT image, after regridding and smoothing them to match the ATCA image. RM is defined as the integral of n e and B || along the line of sight. The thermal X-ray surface brightness, S x , is proportional to n e 2 . Therefore if RM and S x 1/2 are correlated, the Faraday rotation is occurring within the thermal plasma (Matsui et al. 1984). A plot of RM vs. S x 1/2 (Figure 2) shows that there is no clear correlation between RM and S x 1/2 in the remnant, which means that the RMs originate from the ISM/halo along the line-of-sight. Therefore the RM variations across the remnant may reflect the structure of the magnetised interstellar medium (Haverkorn et al. 2004) and the smooth component may tell us about the overall magnetic field morphology within the remnant (Ransom et al. 2008). This will form the basis of our further analysis of these data. 1 / 2 against Rotation Measure for the east (positive) and west (negative) sides of the remnant. A least-squares best fit is plotted onto each data set. On-going workThe following analytical steps will be taken: (1) Modelling of the RM structure across the remnant to determine the large-scale structure and morphology of the magnetic field (i.e. linear, spiral, toroidal) in the remnant (2) Analysis of smaller-scale RM variations across the remnant, to probe the turbulent scale-sizes in the ISM and galactic halo....

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Properties of the warm magnetized ISM, as inferred from WSRT polarimetric imaging

Cited by 26 publications

References 33 publications

WSRT Faraday tomography of the Galactic ISM at λ ~ 0.86 m

WSRT Faraday tomography of the Galactic ISM at λ ~ 0.86 m

Observational tests of the properties of turbulence in the Very Local Interstellar Medium

Spectropolarimetry of supernova remnant G296.5 + 10.0

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