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731. Radio source 111MHz interplan. scintillation. I
ID:
ivo://CDS.VizieR/J/AZh/86/23
Title:
Radio source 111MHz interplan. scintillation. I
Short Name:
J/AZh/86/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
A complete sample of core-dominated radio sources has been studied using the interplanetary-scintillation method. In total, 72 sources were observed, with scintillations detected in 28 of them. The remaining sources have upper limits on their flux densities. Integrated flux densities are estimated for 24 sources. Cut-offs have been observed in the spectra of many sources. The thermal-electron densities have been estimated, assuming that these cut-offs are due to free-free absorption of the synchrotron radio emission.
732. Radio source 111MHz interplan. scintillation. II
ID:
ivo://CDS.VizieR/J/AZh/86/35
Title:
Radio source 111MHz interplan. scintillation. II
Short Name:
J/AZh/86/35
Date:
21 Oct 2021
Publisher:
CDS
Description:
A complete sample of radio sources has been studied using the interplanetary scintillation method. In total, 32 sources were observed, with scintillations detected in 12 of them. The remaining sources have upper limits for the flux densities of their compact components. Integrated flux densities are estimated for 18 sources.
733. Radio structure of Quasars
ID:
ivo://CDS.VizieR/J/AJ/108/1163
Title:
Radio structure of Quasars
Short Name:
J/AJ/108/1163
Date:
21 Oct 2021
Publisher:
CDS
Description:
Images of resolved radio sources in the Palomar Bright Quasar Survey are presented with an angular resolution of 0.5 and 18arcsec. The observed structure of some well resolved radio quiet quasars and AGN's show large scale linear structures or unresolved central cores similar to radio loud objects in the BQS sample as well as the more luminous radio selected quasars. We suggest that at least some of these less luminous radio quiet objects may contain compact central engines characteristic of radio loud quasars and radio galaxies.
734. Radio time delay of gravitational lens 0957+561
ID:
ivo://CDS.VizieR/J/ApJ/510/64
Title:
Radio time delay of gravitational lens 0957+561
Short Name:
J/ApJ/510/64
Date:
21 Oct 2021
Publisher:
CDS
Description:
The gravitational lens 0957+561 was monitored with the Very Large Array from 1979 to 1997. The 6 cm light-curve data from 1995 to 1997 and the 4cm data from 1990 to 1997 are reported here. At 4cm the intrinsic source variations occur earlier and are twice as large as the corresponding variations at 6cm. The VLBI core and jet components have different magnification factors, leading to different flux ratios for the varying and nonvarying portions of the VLA light curves. Using both the Press, Rybicki, & Hewitt Q (1992ApJ...385..404P) and dispersion statistical techniques, we determined the time delay, core flux ratio, and excess nonvarying B image flux density. The fits were performed for the 4 and 6 cm light curves, both individually and jointly, and we used Gaussian Monte Carlo data to estimate 68% statistical confidence levels. The delay estimates from each individual wavelength were inconsistent given the formal uncertainties, suggesting that there are unmodeled systematic errors in the analysis. We roughly estimate the systematic uncertainty in the joint result from the difference between the 6 and 4cm results, giving 409+/-30 days for the PRHQ statistic and 397+/-20 days for the dispersion statistic. These results are consistent with the current optical time delay of 417+/-3 days, reconciling the long-standing difference between the optical and radio light curves and between different statistical analyses.
735. Radio transients in a 1.4GHz drift-scan survey
ID:
ivo://CDS.VizieR/J/ApJ/704/652
Title:
Radio transients in a 1.4GHz drift-scan survey
Short Name:
J/ApJ/704/652
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report two new radio transients at high Galactic latitude, WJN J0951+3300 (RA=09h51m22s+/-10s, DE=33{deg}00'+/-0.4{deg}, b=50{deg}54.2') and WJN J1039+3300 (RA=10h39m26s+/-10s, DE=33{deg}00'+/-0.4{deg}, b=60{deg}58.5'), which were detected by interferometric drift-scan observations at 1.4GHz at the Waseda Nasu Pulsar Observatory. WJN J0951+3300 was detected at 16:49:32UT on 2006 January 12 with the flux density of approximately 1760.5+/-265.9mJy, and WJN J1039+3300 was detected at 17:13:32UT on 2006 January 18 with the flux density of approximately 2242.5+/-228.7mJy. Both of them lasted for a short duration (<=2 days). The possibility that the distribution of the WJN radio transients is isotropic was suggested in a previous study. Having re-evaluated the log N-log S relation with the addition of the two new objects reported in this paper, we find that the slope is consistent with a slope of -1.5 and the previous result. Additionally, although there are several counterparts to WJN radio transients, we found that one of the quasar counterparts within the positional error of WJN J0951+3300 could be a radio-loud quasar. We have discussed whether or not WJN J0951+3300 could be of this quasar origin.
736. Random forests method to discover high-redshift QSOs
ID:
ivo://CDS.VizieR/J/AJ/162/72
Title:
Random forests method to discover high-redshift QSOs
Short Name:
J/AJ/162/72
Date:
14 Mar 2022 07:01:17
Publisher:
CDS
Description:
We present a method of selecting quasars up to redshift ~6 with random forests, a supervised machine-learning method, applied to Pan-STARRS1 and WISE data. We find that, thanks to the increasing set of known quasars, we can assemble a training set that enables supervised machine-learning algorithms to become a competitive alternative to other methods up to this redshift. We present a candidate set for the redshift range 4.8-6.3, which includes the region around z=5.5 where selecting quasars is difficult due to their photometric similarity to red and brown dwarfs. We demonstrate that, under our survey restrictions, we can reach a high completeness (66%{+/-}7% below redshift 5.6/83_-9_^+6^% above redshift 5.6) while maintaining a high selection efficiency (78_-8_^+10^%/94_-8_^+5^% ). Our selection efficiency is estimated via a novel method based on the different distributions of quasars and contaminants on the sky. The final catalog of 515 candidates includes 225 known quasars. We predict the candidate catalog to contain additional 148_-33_^+41^ new quasars below redshift 5.6 and 45_-8_^+5^ above, and we make the catalog publicly available. Spectroscopic follow-up observations of 37 candidates led us to discover 20 new high redshift quasars (18 at 4.6<~z<~5.5, 2z~5.7). These observations are consistent with our predictions on efficiency. We argue that random forests can lead to higher completeness because our candidate set contains a number of objects that would be rejected by common color cuts, including one of the newly discovered redshift 5.7 quasars.
737. R-band light curve of QSO J0158-4325 images
ID:
ivo://CDS.VizieR/J/ApJ/756/52
Title:
R-band light curve of QSO J0158-4325 images
Short Name:
J/ApJ/756/52
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present four new seasons of optical monitoring data and six epochs of X-ray photometry for the doubly imaged lensed quasar Q J0158-4325. The high-amplitude, short-period microlensing variability for which this system is known has historically precluded a time delay measurement by conventional methods. We attempt to circumvent this limitation by the application of a Monte Carlo microlensing analysis technique, but we are only able to prove that the delay must have the expected sign (image A leads image B). Despite our failure to robustly measure the time delay, we successfully model the microlensing at optical and X-ray wavelengths to find a half-light radius for soft X-ray emission log (r_1/2,X,soft_/cm)=14.3^+0.4^_-0.5_, an upper limit on the half-light radius for hard X-ray emission log (r_1/2,X,hard_/cm)<=14.6, and a refined estimate of the inclination-corrected scale radius of the optical R-band (rest frame 3100{AA}) continuum emission region of log (r_s_/cm)=15.6+/-0.3.
738. R-band light curves of DES J0408-5359
ID:
ivo://CDS.VizieR/J/A+A/609/A71
Title:
R-band light curves of DES J0408-5359
Short Name:
J/A+A/609/A71
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present time-delay measurements for the new quadruply imaged quasar DES J0408-5354, the first quadruply imaged quasar found in the Dark Energy Survey (DES). Our result is made possible by implementing a new observational strategy using almost daily observations with the MPIA 2.2m telescope at La Silla observatory and deep exposures reaching a signal-to-noise ratio of about 1000 per quasar image. This data quality allows us to catch small photometric variations (a few mmag rms) of the quasar, acting on temporal scales much shorter than microlensing, hence making the time delay measurement very robust against microlensing. In only 7 months we measure very accurately one of the time delays in DES J0408-5354: Dt(AB)=-112.1+/-2.1-days (1.8%) using only the MPIA 2.2m data. In combination with data taken with the 1.2m Euler Swiss telescope, we also measure two delays involving the D component of the system Dt(AD)=-155.5+/-12.8-days (8.2%) and Dt(BD)=-42.4+/-17.6-days (41%), where all the error bars include systematics. Turning these time delays into cosmological constraints will require deep HST imaging or ground-based Adaptive Optics (AO), and information on the velocity field of the lensing galaxy.
739. R-band light curves of HE 0435-1223
ID:
ivo://CDS.VizieR/J/MNRAS/465/4914
Title:
R-band light curves of HE 0435-1223
Short Name:
J/MNRAS/465/4914
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results from thirteen years of optically monitoring the gravitationally lensed z_QSO_= 1.693 quasar HE 0435-1223. The R-band light curves of the four individual images of the quasar were obtained using deconvolution photometry for a total of 876 epochs. Several sharp quasar variability features strongly constrain the time delays between the quasar images. Using two different numerical techniques, we measured these delays for all possible pairs of quasar images while always processing the four light curves simultaneously. For both methods, the delays are compatible with the previous measurements presented in Courbin et al. (2011, Cat. J/A+A/536/A53) that used a subset of the present data and a different curve-shifting method. Our analysis of random and systematic errors accounts in a realistic way for the observed quasar variability, fluctuating microlensing magnification over a broad range of temporal scales, noise properties, and seasonal gaps. Finally, we find that our time-delay measurement methods yield compatible results when applied to subsets of the data.
740. R-band light curves of HE 0435-1223
ID:
ivo://CDS.VizieR/J/A+A/536/A53
Title:
R-band light curves of HE 0435-1223
Short Name:
J/A+A/536/A53
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010. With seven years of data, we clearly show that quasar image A is affected by strong microlensing variations and that the time delays are best expressed relative to quasar image B.

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