- ID:
- ivo://CDS.VizieR/J/A+A/583/A137
- Title:
- LOFAR-HBA 3C196 field RM cubes
- Short Name:
- J/A+A/583/A137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study aims to characterize linear polarization structures in LOFAR observations of the interstellar medium (ISM) in the 3C196 field, one of the primary fields of the LOFAR-Epoch of Reionization key science project. We have used the high band antennas (HBA) of LOFAR to image this region and Rotation Measure (RM) synthesis to unravel the distribution of polarized structures in Faraday depth. The brightness temperature of the detected Galactic emission is 5-15K in polarized intensity and covers the range from -3 to +8 rad/m^2^ in Faraday depth. The most interesting morphological feature is a strikingly straight filament at a Faraday depth of +0.5 rad/m^2^ running from north to south, right through the centre of the field and parallel to the Galactic plane. There is also an interesting system of linear depolarization canals conspicuous in an image showing the peaks of Faraday spectra. We used the Westerbork Synthesis Radio Telescope (WSRT) at 350MHz to image the same region. For the first time, we see some common morphology in the RM cubes made at 150 and 350MHz. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies and previous LOFAR observations. Based on our results, we determined physical parameters of the ISM and proposed a simple model that may explain the observed distribution of the intervening magneto-ionic medium. The mean line-of-sight magnetic field component is determined to be 0.3-/+0.1uG and its spatial variation across the 3C196 field is 0.1uG. The filamentary structure is probably an ionized filament in the ISM, located somewhere within the Local Bubble. This filamentary structure shows an excess in thermal electron density (n_e_*B_||_>6.2cm^-3^uG) compared to its surroundings.
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- ID:
- ivo://CDS.VizieR/J/A+A/617/A136
- Title:
- LOFAR M51 field low-frequency polarized sources
- Short Name:
- J/A+A/617/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The new generation of broad-band radio continuum surveys will provide large data sets with polarization information. New algorithms need to be developed to extract reliable catalogs of linearly polarized sources that can be used to characterize those sources and produce a dense rotation measure (RM) grid to probe magneto-ionized structures along the line of sight via Faraday rotation. The aim of the paper is to develop a computationally efficient and rigorously defined source-finding algorithm for linearly polarized sources. We used a calibrated data set from the LOw Frequency ARray (LOFAR) at 150MHz centered on the nearby galaxy M51 to search for polarized background sources. With a new imaging software, we re-imaged the field at a resolution of 18''x15'' and cataloged a total of about 3000 continuum sources within 2.5{deg} of the center of M51. We made small Stokes Q and U images centered on each source brighter than 100mJy in total intensity (201 sources) and used RM synthesis to create corresponding Faraday cubes that were analyzed individually. For each source, the noise distribution function was determined from a subset of the measurements at high Faraday depths where no polarization is expected; the peaks in polarized intensity in the Faraday spectrum were identified and the p-value of each source was calculated. Finally, the false discovery rate method was applied to the list of p-values to produce a list of polarized sources and quantify the reliability of the detections. We also analyzed sources fainter than 100mJy but that were reported as polarized in the literature at at least another radio frequency. Of the 201 sources that were searched for polarization, six polarized sources were detected confidently (with a false discovery rate of 5%). This corresponds to a number density of one polarized source per 3.3 square degrees, or 0.3 source per square degree. Increasing the false discovery rate to 50% yields 19 sources. A majority of the sources have a morphology that is indicative of them being double-lobed radio galaxies, and the ones with literature redshift measurements have 0.5<z<1.0. We find that this method is effective in identifying polarized sources, and is well suited for LOFAR observations. In the future, we intend to develop it further and apply it to larger data sets such as the LOFAR Two-meter Survey of the whole northern sky, LOTSS, and the ongoing deep LOFAR observations of the GOODS-North field.
- ID:
- ivo://CDS.VizieR/J/A+A/385/55
- Title:
- Long-Term Polarization of BL Lac
- Short Name:
- J/A+A/385/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Both photometric and polarimetric data of BL Lac were obtained with the .5-m telescopes of the Byurakan station of the Astronomical Institute of St.-Petersburg University.
- ID:
- ivo://CDS.VizieR/J/A+A/574/A125
- Title:
- Long-term radio variations of QSO J1819+3845
- Short Name:
- J/A+A/574/A125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the long-term evolution of the intra-hour variable quasar, J1819+3845, whose variations have been attributed to interstellar scintillation by extremely local turbulent plasma, located only 1-3pc from Earth. The variations in this source ceased some time between June 2006 and February 2007. The evolution of the source spectrum and the long-term lightcurve, and the persistent compactness of the source VLBI structure indicates that the cessation of rapid variability was associated with the passage of the scattering material out of the line of sight to the quasar. We present an analysis of the linear polarization variations and their relation to total intensity variations. The proper motion of polarized features in the quasar jet is found to be subluminal. Systematic time delays between Stokes I, Q and U, in combination with the structure of the source obtained from 8.4GHz VLBI data, confirm the estimate of the screen distance: 1-2pc, making the screen one of the nearest objects to the Solar System. We determine the physical properties of this scattering material. We examine the rotation measures of sources and the diffuse polarized emission in the surrounding region. We place a limit of 10rad/m^2^ on the RM change. The variability of sources near J1819+3845 is used to deduce that the screen must therefore be either very small (~100AU) or patchy.
- ID:
- ivo://CDS.VizieR/J/A+A/548/A90
- Title:
- Looking for the rainbow on exoplanets
- Short Name:
- J/A+A/548/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Looking for the primary rainbow in starlight that is reflected by exoplanets appears to be a promising method to search for liquid water clouds in exoplanetary atmospheres. Ice water clouds, that consist of water crystals instead of water droplets, could potentially mask the rainbow feature in the planetary signal by covering liquid water clouds. Here, we investigate the strength of the rainbow feature for exoplanets that have liquid and icy water clouds in their atmosphere, and calculate the rainbow feature for a realistic cloud coverage of Earth. We calculate flux and polarization signals of starlight that is reflected by horizontally and vertically inhomogeneous Earth-like exoplanets, covered by patchy clouds consisting of liquid water droplets or water ice crystals. The planetary surfaces are black.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A71
- Title:
- LOTSS HETDEX Faraday depth cube
- Short Name:
- J/A+A/623/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Faraday tomography allows us to map diffuse polarized synchrotron emission from our Galaxy and use it to interpret the magnetic field in the interstellar medium (ISM). We have applied Faraday tomography to 60 observations from the LOFAR Two-Meter Sky Survey (LOTSS) and produced a Faraday depth cube mosaic covering 568 square degrees at high Galactic latitudes, at 4.3 angular resolution and 1rad/m^2^ Faraday depth resolution, with a typical noise level of 50-100uJy per point spread function (PSF) per rotation measure spread function (RMSF) (40-80mK/RMSF). While parts of the images are strongly affected by instrumental polarization, we observe diffuse polarized emission throughout most of the field, with typical brightness between 1 and 6K/RMSF, and Faraday depths between -7 and +25rad/m^2^. We observe many new polarization features, some up to 15deg in length. These include two regions with very uniformly structured, linear gradients in the Faraday depth; we measured the steepness of these gradients as 2.6 and 13rad/m^2^/deg. We also observe a relationship between one of the gradients and an HI filament in the local ISM. Other ISM tracers were also checked for correlations with our polarization data and none were found, but very little signal was seen in most tracers in this region. We conclude that the LOTSS data are very well suited for Faraday tomography, and that a full-scale survey with all the LOTSS data has the potential to reveal many new Galactic polarization features and map out diffuse Faraday depth structure across the entire northern hemisphere.
- ID:
- ivo://CDS.VizieR/J/A+A/568/A74
- Title:
- Low-frequency (115-175MHz) image of M51
- Short Name:
- J/A+A/568/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The grand-design spiral galaxy M51 was observed with the LOFAR High Frequency Antennas (HBA) and imaged in total intensity and polarization. This observation covered the frequencies between 115MHz and 175MHz. We produced an image of total emission of M51 at the mean frequency of 151MHz with 20-arcsec resolution and 0.3mJy rms noise, which is the most sensitive image of a galaxy at frequencies below 300MHz so far. The integrated spectrum of total radio emission is well described by a power law, while flat spectral indices in the central region indicates thermal absorption. We observe the disk to extend out to 16kpc and a break in the radial profile near the optical radius of the disk. The radial scale lengths in the inner and outer disks are larger at 151MHz, and the break is smoother at 151MHz than those observed at 1.4GHz. The arm--interarm contrast is lower at 151MHz than at 1400MHz, indicating propagation of cosmic ray electrons (CRE) from spiral arms into interarm regions.
- ID:
- ivo://CDS.VizieR/J/A+A/374/265
- Title:
- LTE spectrum synthesis in magnetic atmospheres
- Short Name:
- J/A+A/374/265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Files table4.dat contain calculated Stokes IQUV local line profiles of Fe II 4923.9 shown in Fig. 4 of this paper. Profile sets are provided for 0.1, 5 and 20kG magnetic fields, with vector orientation {psi}=40{deg}, {phi}=0{deg}, disc centre and eps_fe_=4.6.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A2
- Title:
- MACS J0717.5+3745 polarization int. maps
- Short Name:
- J/A+A/657/A2
- Date:
- 21 Mar 2022 09:20:37
- Publisher:
- CDS
- Description:
- We present wideband (1-6.5 GHz) polarimetric observations, obtained with the Karl G. Jansky Very Large Array (VLA), of the merging galaxy cluster MACS J0717.5+3745, which hosts one of the most complex known radio relic and halo systems. We use both Rotation Measure Synthesis and QU-fitting, and find a reasonable agreement of the results obtained with these methods, in particular, when the Faraday distribution is simple and the depolarization is mild. The relic is highly polarized over its entire length (850kpc), reaching a fractional polarization >30% in some regions. We also observe a strong wavelength-dependent depolarization for some regions of the relic. The northern part of the relic shows a complex Faraday distribution suggesting that this region is located in or behind the intracluster medium (ICM). Conversely, the southern part of the relic shows a Rotation Measure very close to the Galactic foreground, with a rather low Faraday dispersion, indicating very little magnetoionic material intervening the line-of-sight. From spatially resolved polarization analysis, we find that the scatter of Faraday depths correlates with the depolarization, indicating that the tangled magnetic field in the ICM causes the depolarization. We conclude that the ICM magnetic field could be highly turbulent. At the position of a well known narrow-angle-tailed galaxy (NAT), we find evidence of two components clearly separated in Faraday space. The high Faraday dispersion component seems to be associated with the NAT, suggesting the NAT is embedded in the ICM while the southern part of the relic lies in front of it. If true, this implies that the relic and this radio galaxy are not necessarily physically connected and thus, the relic may be not powered by the shock re-acceleration of fossil electrons from the NAT. The magnetic field orientation follows the relic structure indicating a well-ordered magnetic field. We also detect polarized emission in the halo region; however the absence of significant Faraday rotation and a low value of Faraday dispersion suggests the polarized emission, previously considered as the part of the halo, has a shock(s) origin.
- ID:
- ivo://CDS.VizieR/J/A+A/346/955
- Title:
- Magnetic field around the Local Bubble
- Short Name:
- J/A+A/346/955
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue gathers optical polarimetric data, concerning 918 stars, observed by 15 different authors.
