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51. gamma-ray bright blazars optical polarization
ID:
ivo://CDS.VizieR/J/ApJ/833/77
Title:
gamma-ray bright blazars optical polarization
Short Name:
J/ApJ/833/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blazars are highly variable active galactic nuclei that emit radiation at all wavelengths from radio to gamma rays. Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies, and it also varies dramatically. The polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. However, even though numerous measurements have been performed, the mechanisms behind jet creation, composition, and variability are still debated. We performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between 2008 July and 2014 December to investigate the mechanisms of variability and search for a basic relation between the several subclasses of blazars. We identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. Since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in parsec-scale relativistic jets between different types of blazars (flat-spectrum radio quasars vs. BL Lacs) and consequently between different types of radio galaxies (FR I versus FR II).
52. Gamma-ray-loud blazars optical polarization
ID:
ivo://CDS.VizieR/J/MNRAS/442/1693
Title:
Gamma-ray-loud blazars optical polarization
Short Name:
J/MNRAS/442/1693
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the 2013 May-June commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to Rmag of 17 and as low as 0.035 down to 18mag. The hypothesis that the polarization fractions of gamma-ray-loud and gamma-ray-quiet blazars are drawn from the same distribution is rejected at the 3{sigma} level. We therefore conclude that gamma-ray-loud and gamma-ray-quiet sources have different optical polarization properties. This is the first time this statistical difference is demonstrated in optical wavelengths. The polarization fraction distributions of both samples are well described by exponential distributions with averages of <p>=6.4^+0.9^_-0.8_x10^-2^ for gamma-ray-loud blazars, and <p>=3.2^+2.0^_-1.1_x10^-2^ for gamma-ray-quiet blazars. The most probable value for the difference of the means is 3.4^+1.5^_-2.0_x10^-2^. The distribution of polarization angles is statistically consistent with being uniform.
53. G203.7+11.5 21cm and 11cm intensity maps
ID:
ivo://CDS.VizieR/J/A+A/641/A121
Title:
G203.7+11.5 21cm and 11cm intensity maps
Short Name:
J/A+A/641/A121
Date:
21 Oct 2021
Publisher:
CDS
Description:
In soft X-rays, the Monogem ring is an object with a diameter of 25{deg} located in the Galactic anti-centre. It is believed to be a faint, evolved, local supernova remnant. It is not seen at radio wavelengths, as other large supernova remnants are. We study a narrow about 4.5D long, faint Halpha-filament, G203.7+11.5, that is seen towards the centre of the Monogem ring. It causes depolarisation and excessive Faraday rotation of radio polarisation data. Polarisation observations at 11cm and 21cm with the Effelsberg 100-m telescope were analysed.
54. 6.7GHz methanol maser polarization in MSFRs IV
ID:
ivo://CDS.VizieR/J/A+A/623/A130
Title:
6.7GHz methanol maser polarization in MSFRs IV
Short Name:
J/A+A/623/A130
Date:
21 Oct 2021
Publisher:
CDS
Description:
Magnetohydrodynamical simulations show that the magnetic field can drive molecular outflows during the formation of massive protostars. The best probe to observationally measure both the morphology and the strength of this magnetic field at scales of 10-100au is maser polarization. Measuring the direction of magnetic fields at milliarcsecond resolution around a sample of massive star forming regions to determine whether there exists a relation between the orientation of the magnetic field and of the outflows. In addition by estimating the magnetic field strength via the Zeeman splitting measurements, the role of magnetic field in the dynamics of the massive star-forming region is investigated. We selected a flux-limited sample of 31 massive star-forming regions to perform a statistical analysis of the magnetic field properties with respect to the molecular outflows characteristics. We report the linearly and circularly polarized emission of 6.7GHz CH_3_OH masers towards seven massive star-forming regions of the total sample with the European VLBI Network. The sources are: G23.44-0.18, G25.83-0.18, G25.71-0.04, G28.31-0.39, G28.83-0.25, G29.96-0.02, and G43.80-0.13. We identified a total of 219 CH_3_OH maser features, 47 and 2 of which showed linearly and circularly polarized emission, respectively. We measured well ordered linear polarization vectors around all the massive young stellar objects and Zeeman splitting towards G25.71-0.04 and G28.83-0.25. Thanks to recent theoretical results, we were able to provide lower limits to the magnetic field strength from our Zeeman splitting measurements. We further confirm (based on ~80% of the total flux-limited sample) that the magnetic field on scales of 10-100 au is preferentially oriented along the outflow axes. The estimated magnetic field strength of |B_||_|>61mG and >21mG towards G25.71-0.04 and G28.83-0.2, respectively, indicates that it dominates the dynamics of the gas in both regions.
55. 6.7GHz methanol maser polarization in SFR
ID:
ivo://CDS.VizieR/J/A+A/578/A102
Title:
6.7GHz methanol maser polarization in SFR
Short Name:
J/A+A/578/A102
Date:
21 Oct 2021
Publisher:
CDS
Description:
Theoretical simulations and observations at different angular resolutions have shown that magnetic fields have a central role in massive star formation. Like in low-mass star formation, the magnetic field in massive young stellar objects can either be oriented along the outflow axis or randomly. Measuring the magnetic field at milliarcsecond resolution (10-100au) around a substantial number of massive young stellar objects permits determining with a high statistical significance whether the direction of the magnetic field is correlated with the orientation of the outflow axis or not. In late 2012, we started a large VLBI campaign with the European VLBI Network to measure the linearly and circularly polarized emission of 6.7GHz CH_3_OH masers around a sample of massive star-forming regions. This paper focuses on the first seven observed sources, G24.78+0.08, G25.65+1.05, G29.86-0.04, G35.03+0.35, G37.43+1.51, G174.20-0.08, and G213.70-12.6. For all these sources, molecular outflows have been detected in the past. We detected a total of 176 CH_3_OH masing cloudlets toward the seven massive star-forming regions, 19% of which show linearly polarized emission. The CH_3_OH masers around the massive young stellar object MM1 in G174.20-0.08 show neither linearly nor circularly polarized emission. The linear polarization vectors are well ordered in all the other massive young stellar objects. We measured significant Zeeman splitting toward both A1 and A2 in G24.78+0.08, and toward G29.86-0.04 and G213.70-12.6. By considering all the 19 massive young stellar objects reported in the literature for which both the orientation of the magnetic field at milliarcsecond resolution and the orientation of outflow axes are known, we find evidence that the magnetic field (on scales 10-100au) is preferentially oriented along the outflow axes.
56. GHz-peaked spectrum (GPS) sources
ID:
ivo://CDS.VizieR/J/A+A/482/483
Title:
GHz-peaked spectrum (GPS) sources
Short Name:
J/A+A/482/483
Date:
21 Oct 2021
Publisher:
CDS
Description:
Gigahertz-peaked spectrum (GPS) sources and high frequency peakers (HFPs) are among the smallest of active galactic nuclei currently believed to represent the earliest phases in the evolution of extragalactic radio sources. Recently there has been evidence of contamination by other types of radio sources among the GPS and HFP samples, but the confirmed GPS sources or HFPs also seem to form a very heterogeneous population. We study the statistical clustering of the GPS sources and the HFPs by taking as many source parameters as possible to find homogeneous groups among the sources. We expect the clustering to give us insight into the physical parameters that play a role in different source populations. We have collected a sample of 206 GPS sources and HFPs from the literature and gathered a massive database of various source properties, such as the redshift, the size, the polarization, the magnitudes, and the properties of the radio continuum. To visualize and to cluster these multidimensional data we used self-organising maps (SOM), which are neural networks trained by an unsupervised algorithm. We have classified the sources with an auxiliary classification to trace the locations of different types of radio continuum spectra on the map.
57. 28-40GHz variability and polarimetry
ID:
ivo://CDS.VizieR/J/MNRAS/502/4779
Title:
28-40GHz variability and polarimetry
Short Name:
J/MNRAS/502/4779
Date:
21 Oct 2021
Publisher:
CDS
Description:
We observed 51 sources in the Q-U-I JOint TEnerife (QUIJOTE) cosmological fields which were brighter than 1Jy at 30GHz in the Planck Point Source Catalogue (version 1), with the Very Large Array at 28-40GHz, in order to characterise their high-radio-frequency variability and polarization properties. We find a roughly log-normal distribution of polarization fractions with a median of 2%, in agreement with previous studies, and a median rotation measure (RM) of ~1110rad/m^2^ with one outlier up to ~64000rad/m^2^ which is among the highest RMs measured in quasar cores. We find hints of a correlation between the total intensity flux density and median polarization fraction. We find 59% of sources are variable in total intensity, and 100% in polarization at 3{sigma} level, with no apparent correlation between total intensity variability and polarization variability. This indicates that it will be difficult to model these sources without simultaneous polarimetric monitoring observations and they will need to be masked for cosmological analysis.
58. GLOSTAR Galactic plane survey. II. SNR.
ID:
ivo://CDS.VizieR/J/A+A/651/A86
Title:
GLOSTAR Galactic plane survey. II. SNR.
Short Name:
J/A+A/651/A86
Date:
17 Jan 2022 00:20:41
Publisher:
CDS
Description:
The properties of the population of Galactic supernova remnants (SNRs) are essential to our understanding of the dynamics of the interstellar medium (ISM) in the Milky Way. However, the completeness of the catalog of Galactic SNRs is expected to be only ~30%, with on order 700 SNRs yet to be detected. Deep interferometric radio continuum surveys of the Galactic plane help in rectifying this apparent deficiency by identifying low surface brightness SNRs and compact SNRs that have not been detected in previous surveys. However, SNRs are routinely confused with HII regions, which can have similar radio morphologies. Radio spectral index, polarization, and emission at mid-infrared (MIR) wavelengths can help distinguish between SNRs and HII regions. We aim to identify SNR candidates using continuum images from the Karl G. Jansky Very Large Array GLObal view of the STAR formation in the Milky Way (GLOSTAR) survey. GLOSTAR is a C-band (4-8GHz) radio wavelength survey of the Galactic plane covering 358{deg}>=l<=60{deg}, |b|<=1{deg}. The continuum images from this survey, which resulted from observations with the most compact configuration of the array, have an angular resolution of 18''. We searched for SNRs in these images to identify known SNRs, previously identified SNR candidates, and new SNR candidates. We study these objects in MIR surveys and the GLOSTAR polarization data to classify their emission as thermal or nonthermal. We identify 157 SNR candidates, of which 80 are new. Polarization measurements provide evidence of nonthermal emission from 9 of these candidates. We find that two previously identified candidates are filaments. We also detect emission from 91 of the 94 known SNRs in the survey region. Four of these are reclassified as HII regions following detection in MIR surveys. The better sensitivity and resolution of the GLOSTAR data have led to the identification of 157 SNR candidates, along with the reclassification of several misidentified objects. We show that the polarization measurements can identify nonthermal emission, despite the diffuse Galactic synchrotron emission. These results underscore the importance of higher resolution and higher sensitivity radio continuum data in identifying and confirming SNRs.
59. GMVA 86GHz Stokes IQU images of 3C84 jet
ID:
ivo://CDS.VizieR/J/A+A/622/A196
Title:
GMVA 86GHz Stokes IQU images of 3C84 jet
Short Name:
J/A+A/622/A196
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report results from a deep polarization imaging of the nearby radio galaxy 3C 84 (NGC 1275). The source was observed with the Global Millimeter VLBI Array (GMVA) at 86GHz at an ultrahigh angular resolution of 50{mu}as (corresponding to 200Rs). We also add complementary multiwavelength data from the Very Long Baseline Array (VLBA; 15 & 43GHz) and from the Atacama Large Millimeter/submillimeter Array (ALMA; 97.5, 233.0, and 343.5GHz). At 86GHz, we measured a fractional linear polarization of ~2% in the VLBI core region. The polarization morphology suggests that the emission is associated with an underlying limb-brightened jet. The fractional linear polarization is lower at 43 and 15GHz (~0.3-0.7% and <0.1%, respectively). This suggests an increasing linear polarization degree toward shorter wavelengths on VLBI scales. We also obtain a large rotation measure (RM) of ~10^5-6^rad/m^2^ in the core at >~43GHz. Moreover, the VLBA 43GHz observations show a variable RM in the VLBI core region during a small flare in 2015. Faraday depolarization and Faraday conversion in an inhomogeneous and mildly relativistic plasma could explain the observed linear polarization characteristics and the previously measured frequency dependence of the circular polarization. Our Faraday depolarization modeling suggests that the RM most likely originates from an external screen with a highly uniform RM distribution. To explain the large RM value, the uniform RM distribution, and the RM variability, we suggest that the Faraday rotation is caused by a boundary layer in a transversely stratified jet. Based on the RM and the synchrotron spectrum of the core, we provide an estimate for the magnetic field strength and the electron density of the jet plasma.
60. G31.41+0.31 Stokes IQU images
ID:
ivo://CDS.VizieR/J/A+A/630/A54
Title:
G31.41+0.31 Stokes IQU images
Short Name:
J/A+A/630/A54
Date:
21 Oct 2021
Publisher:
CDS
Description:
Submillimeter Array (SMA) 870um polarization observations of the hot molecular core G31.41+0.31 revealed one of the clearest examples up to date of an hourglass-shaped magnetic field morphology in a high-mass star-forming region. To better establish the role that the magnetic field plays in the collapse of G31.41+0.31, we carried out Atacama Large Millimeter/submillimeter Array (ALMA) observations of the polarized dust continuum emission at 1.3mm with an angular resolution four times higher than that of the previous (sub)millimeter observations to achieve an unprecedented image of the magnetic field morphology. We used ALMA to perform full polarization observations at 233GHz (Band 6). The resulting synthesized beam is 00.28"x00.20" which, at the distance of the source, corresponds to a spatial resolution of 875au. The observations resolve the structure of the magnetic field in G31.41+0.31 and allow us to study the field in detail. The polarized emission in the Main core of G31.41+0.41 is successfully fit with a semi-analytical magnetostatic model of a toroid supported by magnetic fields. The best fit model suggests that the magnetic field is well represented by a poloidal field with a possible contribution of a toroidal component of 10% of the poloidal component, oriented southeast to northwest at ~-44{deg} and with an inclination of ~-45{deg}. The magnetic field is oriented perpendicular to the northeast to southwest velocity gradient detected in this core on scales from 10^3^-10^4^au. This supports the hypothesis that the velocity gradient is due to rotation of the core and suggests that such a rotation has little effect on the magnetic field. The strength of the magnetic field estimated in the central region of the core with the Davis-Chandrasekhar-Fermi method is ~8-13mG and implies that the mass-to-flux ratio in this region is slightly supercritical ({lambda}=1.4-2.2). The magnetic field in G31.41+0.31 maintains an hourglass-shaped morphology down to scales of <1000au. Despite the magnetic field being important in G31.41+0.31, it is not enough to prevent fragmentation and collapse of the core, as demonstrated by the presence of at least four sources embedded in the center of the core.