- 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.
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Search Results
- 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/ApJS/213/3
- Title:
- Low-frequency flat spectrum sources (LORCAT)
- Short Name:
- J/ApJS/213/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A well known property of the {gamma}-ray sources detected by Cos-B in the 1970s, by the Compton Gamma-Ray Observatory in the 1990s, and recently by the Fermi observations is the presence of radio counterparts, particularly for those associated with extragalactic objects. This observational evidence is the basis of the radio-{gamma}-ray connection established for the class of active galactic nuclei known as blazars. In particular, the main spectral property of the radio counterparts associated with {gamma}-ray blazars is that they show a flat spectrum in the GHz frequency range. Our recent analysis dedicated to search blazar-like candidates as potential counterparts for the unidentified {gamma}-ray sources allowed us to extend the radio-{gamma}-ray connection in the MHz regime. We also showed that blazars below 1GHz maintain flat radio spectra. Thus, on the basis of these new results, we assembled a low-frequency radio catalog of flat-spectrum sources built by combining the radio observations of the Westerbork Northern Sky Survey and of the Westerbork in the southern hemisphere catalog with those of the NRAO Very Large Array Sky survey (NVSS). This could be used in the future to search for new, unknown blazar-like counterparts of {gamma}-ray sources. First, we found NVSS counterparts of Westerbork Synthesis Radio Telescope radio sources, and then we selected flat-spectrum radio sources according to a new spectral criterion, specifically defined for radio observations performed below 1GHz. We also described the main properties of the catalog listing 28358 radio sources and their logN-logS distributions. Finally, a comparison with the Green Bank 6cm radio source catalog was performed to investigate the spectral shape of the low-frequency flat-spectrum radio sources at higher frequencies.
- 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/ApJ/846/44
- Title:
- Luminous persistent sources in nearby galaxies search
- Short Name:
- J/ApJ/846/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The localization of the repeating fast radio burst (FRB), FRB 121102, suggests that it is associated with a persistent radio-luminous compact source in the FRB host galaxy. Using the FIRST radio catalog, I present a search for luminous persistent sources in nearby galaxies, with radio luminosities >10% of the FRB 121102 persistent source luminosity. The galaxy sample contains about 30% of the total galaxy g-band luminosity within <108Mpc, in a footprint of 10600deg^2^. After rejecting sources likely due to active galactic nuclei activity or background sources, I am left with 11 candidates that are presumably associated with galactic disks or star-formation regions. At least some of these candidates are likely to be due to chance alignment. In addition, I find 85 sources within 1" of galactic nuclei. Assuming that the radio persistent sources are not related to galactic nuclei and that they follow the galaxy g-band light, the 11 sources imply a 95% confidence upper limit on the space density of luminous persistent sources of <~5x10^-5^Mpc^-3^, and that at any given time only a small fraction of galaxies host a radio-luminous persistent source (<~10^-3^L_*_^-1^). Assuming a persistent source lifetime of 100 years, this implies a birth rate of <~5x10^-7^yr^-1^Mpc^-3^. Given the FRB volumetric rate, and assuming that all FRBs repeat and are associated with persistent radio sources, this sets a lower limit on the rate of FRB events per persistent source of >~0.8yr^-1^. I argue that these 11 candidates are good targets for FRB searches and I estimate the FRB event rate from these candidates.
- ID:
- ivo://CDS.VizieR/J/A+AS/80/215
- Title:
- Lunar occultations of weak radio sources
- Short Name:
- J/A+AS/80/215
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog contains the results of lunar occultation observations of 106 radio sources within declination +/- 19 degrees at 327 MHz. There are 171 sources listed in the catalog due to multiple components for some of the radio sources. Flux densities were measured at 327 MHz by lunar occultation with the Ooty Telescope. Flux densities have also been measured at 18 cm (1669 MHz) and 21 cm (1413 MHz) using the Nancay telescope. Optical identifications on the basis of the radio positions and angular structures are given. This catalog is a merge of table 1 and table 2 from the publication.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/1029
- Title:
- Magnetic field in the SMC
- Short Name:
- J/ApJ/688/1029
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the magnetic field of the Small Magellanic Cloud (SMC), carried out using radio Faraday rotation and optical starlight polarization data. Consistent negative rotation measures (RMs) across the SMC indicate that the line-of-sight magnetic field is directed uniformly away from us with a strength 0.19+/-0.06{mu}G. Applying the Chandrasekhar-Fermi method to starlight polarization data yields an ordered magnetic field in the plane of the sky of strength 1.6+/-0.4uG oriented at a position angle 4+/-12{deg}, measured counterclockwise from the great circle on the sky joining the SMC to the Large Magellanic Cloud (LMC). We construct a three-dimensional magnetic field model of the SMC, under the assumption that the RMs and starlight polarization probe the same underlying large-scale field. further test the pan-Magellanic field hypothesis.
158. MAGPIS 20cm survey
- ID:
- ivo://CDS.VizieR/J/AJ/131/2525
- Title:
- MAGPIS 20cm survey
- Short Name:
- J/AJ/131/2525
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Multi-Array Galactic Plane Imaging Survey (MAGPIS), which maps portions of the first Galactic quadrant with an angular resolution, sensitivity, and dynamic range that surpass existing radio images of the Milky Way by more than an order of magnitude. The source detection threshold at 20cm is in the range 12mJy over the 85% of the survey region (5{deg}<l<32{deg}, |b|<0.8{deg}) not covered by bright extended emission; the angular resolution is ~6". We catalog over 3000 discrete sources (diameters mostly <30") and present an atlas of ~400 diffuse emission regions. New and archival data at 90cm for the whole survey area are also presented. Comparison of our catalogs and images with the Midcourse Space Experiment mid-infrared data allows us to provide preliminary discrimination between thermal and nonthermal sources. We identify 49 high-probability supernova remnant candidates, increasing by a factor of 7 the number of known remnants with diameters smaller than 5' in the survey region; several are pulsar wind nebula candidates and/or very small diameter remnants (D<45").
- ID:
- ivo://CDS.VizieR/J/A+A/555/A23
- Title:
- M82-A radio continuum and polarisation study I.
- Short Name:
- J/A+A/555/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to study the cosmic ray propagation and determine the magnetic field strength and dominant loss processes in the nearby prototypical starbursting galaxy M82, a multi-frequency analysis at four radio wavelengths is presented. Archival data from the Westerbork Synthesis Radio Telescope (WSRT) was reduced and a new calibration technique introduced to reach the high dynamic ranges needed for the complex source morphology. These data were combined with archival Very Large Array (VLA) data, yielding total power maps at {lambda}3cm, {lambda}6cm, {lambda}22cm, and {lambda}92cm. The data show a confinement of the emission at wavelengths of {lambda}3/{lambda}6cm to the core region and a largely extended halo reaching up to 4kpc away from the galaxy midplane at wavelengths of {lambda}22/{lambda}92cm up to a sensitivity limit of 90uJy and 1.8mJy respectively indicating different physical processes in the core and halo regions. The results are used to calculate the magnetic field strength to 98uG in the core region and to 24uG in the halo regions. From the observation of ionisation losses, the filling factor of the ionised medium could be estimated to 2%. This leads to a revised view of the magnetic field distribution in the core region and the propagation processes from the core into the halo regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/689/108
- Title:
- MASIV survey. II. First four epochs
- Short Name:
- J/ApJ/689/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the variability of 443 flat-spectrum, compact radio sources monitored using the VLA for 3 days in four epochs at ~4 month intervals at 5GHz as part of the Micro-Arcsecond Scintillation-Induced Variability (MASIV) survey. Over half of these sources exhibited 2%-10% rms variations on timescales over 2 days. We analyzed the variations by two independent methods and find that the rms variability amplitudes of the sources correlate with the emission measure in the ionized interstellar medium along their respective lines of sight. We thus link the variations with interstellar scintillation of components of these sources, with some (unknown) fraction of the total flux density contained within a compact region of angular diameter in the range 10-50{mu}as. We also find that the variations decrease for high mean flux density sources and, most importantly, for high-redshift sources. The decrease in variability is probably due either to an increase in the apparent diameter of the source or to a decrease in the flux density of the compact fraction beyond z~2.
