- ID:
- ivo://CDS.VizieR/J/A+A/601/A12
- Title:
- S5 0716+714 VLBI K- and Q-band variability
- Short Name:
- J/A+A/601/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study aims to search for the existence of intraday variability (IDV) of BL Lac object S5 0716+714 at high radio frequencies for which the interstellar scintillation effect is not significant. Using the 21-m radio telescope of the Korean VLBI Network (KVN), we present results of multi-epoch simultaneous dual-frequency radio observations. Single-dish observations of S5 0716+714 were simultaneously conducted at 21.7GHz (K-band) and 42.4GHz (Q-band), with a high cadence of 30-60min intervals. We observed four epochs between December 2009 and June 2010. Over the whole set of observation epochs, S5 0716+714 showed significant inter-month variations in flux density at both the K- and Q-bands, with modulation indices of approximately 19% for the K-band and approximately 36% for the Q-band. In all epochs, no clear intraday variability was detected at either frequency. The source shows monotonic flux density increase in epochs 1 and 3 and monotonic flux density decrease in epochs 2 and 4. In the flux density increasing phases, the flux densities at the Q-band increase more rapidly. In the decreasing phase, no significant flux density difference is seen at the two frequencies. The situation could be different close to flux density peaks that we did not witness in our observations. We find an inverted spectrum with mean spectral indices, {bar}{alpha}(S_{nu}_{prop.to}{nu}^-{alpha}^), of -0.57+/-0.13 in epoch 1 and -0.15+/-0.11 in epoch 3. On the other hand, we find relatively steep indices of +0.24+/-0.14 and +0.17+/-0.18 in epochs 2 and 4, respectively. We conclude that the frequency dependence of the variability and the change of the spectral index are caused by source-intrinsic effects rather than by any extrinsic scintillation effect.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/3265
- Title:
- Swift J1745-26 polarized jet
- Short Name:
- J/MNRAS/437/3265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Swift J1745-26 is an X-ray binary towards the Galactic Centre that was detected when it went into outburst in 2012 September. This source is thought to be one of a growing number of sources that display `failed outbursts', in which the self-absorbed radio jets of the transient source are never fully quenched and the thermal emission from the geometrically thin inner accretion disc never fully dominates the X-ray flux. We present multifrequency data from the Very Large Array, Australia Telescope Compact Array and Karoo Array Telescope (KAT-7) radio arrays, spanning the entire period of the outburst. Our rich data set exposes radio emission that displays a high level of large-scale variability compared to the X-ray emission and deviations from the standard radio-X-ray correlation that are indicative of an unstable jet and confirm the outburst's transition from the canonical hard state to an intermediate state. We also observe steepening of the spectral index and an increase of the linear polarization to a large fraction (~50%) of the total flux, as well as a rotation of the electric vector position angle. These are consistent with a transformation from a self-absorbed compact jet to optically thin ejecta - the first time such a discrete ejection has been observed in a failed outburst - and may imply a complex magnetic field geometry.
- ID:
- ivo://CDS.VizieR/J/ApJS/208/25
- Title:
- Swift X-ray observations of 1FGL sources
- Short Name:
- J/ApJS/208/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed all the archival X-ray data of 134 unidentified (unID) gamma-ray sources listed in the first Fermi/LAT (1FGL) catalog and subsequently followed up by the Swift/XRT. We constructed the spectral energy distributions (SEDs) from radio to gamma-rays for each X-ray source detected, and tried to pick up unique objects that display anomalous spectral signatures. In these analyses, we target all the 1FGL unID sources, using updated data from the second Fermi/LAT (2FGL) catalog on the Large Area Telescope (LAT) position and spectra. We found several potentially interesting objects, particularly three sources, 1FGL J0022.2-1850, 1FGL J0038.0+1236, and 1FGL J0157.0-5259, which were then more deeply observed with Suzaku as a part of an AO-7 program in 2012. We successfully detected an X-ray counterpart for each source whose X-ray spectra were well fitted by a single power-law function. The positional coincidence with a bright radio counterpart (currently identified as an active galactic nucleus, AGN) in the 2FGL error circles suggests these sources are definitely the X-ray emission from the same AGN, but their SEDs show a wide variety of behavior. In particular, the SED of 1FGL J0038.0+1236 is not easily explained by conventional emission models of blazars. The source 1FGL J0022.2-1850 may be in a transition state between a low-frequency peaked and a high-frequency peaked BL Lac object, and 1FGL J0157.0-5259 could be a rare kind of extreme blazar.
1654. SXDF 100{mu}Jy catalogue
- ID:
- ivo://CDS.VizieR/J/MNRAS/372/741
- Title:
- SXDF 100{mu}Jy catalogue
- Short Name:
- J/MNRAS/372/741
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe deep radio imaging at 1.4GHz of the 1.3-deg^2^ Subaru/XMM-Newton Deep Field (SXDF), made with the Very Large Array in B and C configurations. We present a radio map of the entire field, and a catalogue of 505 sources covering 0.8deg^2^ to a peak flux density limit of 100uJy. Robust optical identifications are provided for 90 per cent of the sources, and suggested identifications are presented for all but 14 (of which seven are optically blank, and seven are close to bright contaminating objects). We show that the optical properties of the radio sources do not change with flux density, suggesting that active galactic nuclei (AGN) continue to contribute significantly at faint flux densities. We test this assertion by cross-correlating our radio catalogue with the X-ray source catalogue and conclude that radio-quiet AGN become a significant population at flux densities below 300uJy, and may dominate the population responsible for the flattening of the radio source counts if a significant fraction of them are Compton-thick.
- ID:
- ivo://CDS.VizieR/VIII/78
- Title:
- Sydney University Molonglo Sky Survey (SUMSS)
- Short Name:
- VIII/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sydney University Molonglo Sky Survey (SUMSS) is being carried out at 843MHz with the Molonglo Observatory Synthesis Telescope (MOST) in its upgraded wide-field capability. The survey consists of 4.3x4.3{deg} mosaic images with 45x45''cosec{delta} resolution, covering 8000 square degrees from -30 degrees declination southwards. The survey resolution and sensitivity (1-sigma noise limit 1mJy) are well-matched to the NRAO VLA Sky Survey (NVSS) so that together NVSS and SUMSS will provide a complete survey of the radio sky. The version 1.7 (01-Jun-2006) of the catalogue consists of 205676 radio sources made by fitting elliptical gaussians in 671 SUMSS mosaics to a limiting peak brightness of 6mJy/beam at declination <-50{deg}, and 10mJy/beam at declination >-50{deg}. Positional accuracies are 1-2'' for sources with S_p_>=20mJy/beam, and are always better than 10''. The internal flux density scale is accurate to 3%. Image artefacts have been classified using a decision tree, which correctly identifies and rejects spurious sources in over 96% of cases. See the SUMSS site at http://www.astrop.physics.usyd.edu.au/sumsscat/ for details about all versions of the SUMSS, and an access to the mosaic images.
- ID:
- ivo://CDS.VizieR/VIII/81B
- Title:
- Sydney University Molonglo Sky Survey (SUMSS V2.1)
- Short Name:
- VIII/81B
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sydney University Molonglo Sky Survey (SUMSS) is carried out at 843MHz with the Molonglo Observatory Synthesis Telescope (MOST) in its upgraded wide-field capability. The survey consists of 4.3x4.3{deg} mosaic images with 45x45''cosec{delta} resolution, covering 8000 square degrees from -30 degrees declination southwards with |b|>10{deg}. The survey resolution and sensitivity (1-sigma noise limit 1mJy) are well-matched to the NRAO VLA Sky Survey (NVSS) so that together NVSS and SUMSS provide a complete survey of the radio sky. The version 2.0 (08-Aug-2007) of the catalogue consists of 210412 radio sources made by fitting elliptical gaussians in 633 SUMSS mosaics to a limiting peak brightness of 6mJy/beam at declination <-50{deg}, and 10mJy/beam at declination >-50{deg}. Positional accuracies are 1-2'' for sources with S_p_>=20mJy/beam, and are always better than 10''. The internal flux density scale is accurate to 3%. Image artefacts have been classified using a decision tree, which correctly identifies and rejects spurious sources in over 96% of cases. See the SUMSS site at http://www.astrop.physics.usyd.edu.au/sumsscat/ for details about all versions of the SUMSS, and an access to the mosaic images. The version 2.1 (from 2008-03-11) corrects a bug in 2.0 in which some bright (S>500 mJy) sources were missing from the catalogue.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A94
- Title:
- Temperature structures in Galactic center clouds
- Short Name:
- J/A+A/595/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Central Molecular Zone (CMZ) at the center of our Galaxy is the best template to study star formation processes under extreme conditions, similar to those in high-redshift galaxies. We observed on-the-fly maps of para-H_2_CO transitions at 218GHz and 291GHz with the Atacama Pathfinder Experiment (APEX) telescope towards seven Galactic center clouds. From the temperature-sensitive integrated intensity line ratios of H_2_CO(3_21_-2_20_)/H_2_CO(3_03_-2_02_) and H_2_CO(4_22_-3_21_)/H_2_CO(4_04_-3_03_) in combination with radiative transfer models, we produce gas temperature maps of our targets. Our targets have a complex velocity structure that requires a careful disentanglement of the different components. We produce temperature maps for each of the velocity components and show that the temperatures of the components differ, revealing temperature gradients in the clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A68
- Title:
- TeV/non-TeV BL Lacs multi-lambda fluxes
- Short Name:
- J/A+A/608/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have collected the most complete multi-wavelength (6.0-6.0E^-18^cm) dataset of very high energy (VHE) gamma-ray emitting (TeV) BL Lacs, which are the most numerous extragalactic VHE sources. Using significant correlations between different bands, we aim to identify the best TeV BL Lac candidates that can be discovered by the current and next generation of imaging air Cherenkovtelescopes. We formed five datasets from lower energy data, i.e. radio, mid-infrared, optical, X-rays, and GeV gamma-ray, and five VHE gamma-ray datasets to perform a correlation study between different bands and to construct the prediction method. The low energy datasets were averaged for individual sources, while the VHE gamma-ray data were divided into subsets according to the flux state of the source. We then looked for significant correlations and determined their best-fit parameters. Using the best-fit parameters we predicted the level of VHE gamma-ray flux for a sample of 182 BL Lacs, which have not been detected at TeV energies. We identified the most promising TeV BL Lac candidates based on the predicted VHE gamma-ray flux for each source. We found 14 significant correlations between radio, mid-infrared, optical, gamma-ray, and VHE gamma-ray bands. The correlation between optical and VHE gamma-ray luminosity is established for the first time. We attribute this to the more complete sample and more accurate handling of host galaxy flux in our work. We found nine BL Lac candidates whose predicted VHE gamma-ray flux is high enough for detection in less than 25 hours with current imaging air Cherenkov telescopes.
- ID:
- ivo://CDS.VizieR/VIII/42
- Title:
- Texas Survey of radio sources at 365MHz
- Short Name:
- VIII/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Texas Survey of discrete radio sources between -35.5deg and 71.5deg declination (B1950), which was carried out at 365MHz with the Texas Interferometer during 1974-1983. The Survey lists accurate positions with internal errors of about an arcsecond, flux densities which for strong point sources have internal errors of about 1% and total errors of about 5%, simple structure models and indications of spectrum and variability for 66841 sources. Results of comparisons with other data are presented, and show that the Survey is 90% complete at 0.4Jy and 80% complete at 0.25Jy, is nearly free from spurious sources, and has a lobeshift incidence which is reasonably described by quality flags associated with each source.
- ID:
- ivo://CDS.VizieR/VIII/87
- Title:
- The Allen Telescope Array 20cm Survey (ATATS). I.
- Short Name:
- VIII/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch (12 visits), 690deg^2^ radio image and catalog at 1.4GHz. The survey is designed to detect rare, very bright transients as well as to verify the capabilities of the ATA to form large mosaics. The combined image using data from all 12 ATATS epochs has rms noise {sigma}=3.94mJy/beam and dynamic range 180, with a circular beam of 150" FWHM. It contains 4408 sources to a limiting sensitivity of 5{sigma}=20mJy/beam. We compare the catalog generated from this 12 epoch combined image to the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency, and find that we can measure source positions to better than ~20". For sources above the ATATS completeness limit, the median flux density is 97% of the median value for matched NVSS sources, indicative of an accurate overall flux calibration. We examine the effects of source confusion due to the effects of differing resolution between ATATS and NVSS on our ability to compare flux densities. We detect no transients at flux densities greater than 40mJy in comparison with NVSS and place a 2{sigma} upper limit of 0.004deg^-2^ on the transient rate for such sources. These results suggest that the >~1Jy transients reported by Matsumara et al. may not be true transients, but rather variable sources at their flux density threshold.
