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Start Over Subject quasars Content Level Research
421. Lensed QSOs light curves & spectral monitoring
ID:
ivo://CDS.VizieR/J/A+A/616/A118
Title:
Lensed QSOs light curves & spectral monitoring
Short Name:
J/A+A/616/A118
Date:
21 Oct 2021
Publisher:
CDS
Description:
In the framework of the Gravitational LENses and DArk MAtter (GLENDAMA) project, we present a database of nine gravitationally lensed quasars (GLQs) that have two or four images brighter than r=20mag and are located in the northern hemisphere. This new database consists of a rich variety of follow-up observations included in the GLENDAMA global archive, which is publicly available online and contains 6557 processed astronomical frames of the nine lens systems over the period 1999-2016. In addition to the GLQs, our archive also incorporates binary quasars, accretion-dominated radio-loud quasars, and other objects, where about 50% of the non-GLQs were observed as part of a campaign to identify GLQ candidates. Most observations of GLQs correspond to an ongoing long-term macro-programme with 2-10m telescopes at the Roque de los Muchachos Observatory, and these data provide information on the distribution of dark matter at all scales. We outline some previous results from the database, and we additionally obtain new results for several GLQs that update the potential of the tool for astrophysical studies.
422. Lensed QSO UM673/Q0142-100 VRi light curves
ID:
ivo://CDS.VizieR/J/A+A/551/A104
Title:
Lensed QSO UM673/Q0142-100 VRi light curves
Short Name:
J/A+A/551/A104
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present four years of photometric observations of the doubly imaged quasar UM673, carried out in three filters (VRi) with the Danish 1.54m telescope at the La Silla Observatory. We studied the variations in flux and in color index of each lensed component as a function of time, and we obtained an independent estimation of the magnitude of the faint lens galaxy, showing that its contribution cannot be neglected.
423. 2 lensed quasars light curves
ID:
ivo://CDS.VizieR/J/A+A/553/A121
Title:
2 lensed quasars light curves
Short Name:
J/A+A/553/A121
Date:
21 Oct 2021
Publisher:
CDS
Description:
Within the framework of the COSMOGRAIL collaboration we present 7- and 8.5-year-long light curves and time-delay estimates for two gravitationally lensed quasars: SDSS J1206+4332 and HS 2209+1914. We monitored these doubly lensed quasars in the R-band using four telescopes: the Mercator, Maidanak, Himalayan Chandra, and Euler Telescopes, together spanning a period of 7 to 8.5 observing seasons from mid-2004 to mid-2011. The photometry of the quasar images was obtained through simultaneous deconvolution of these data. The time delays were determined from these resulting light curves using four very different techniques: a dispersion method, a spline fit, a regression difference technique, and a numerical model fit. This minimizes the bias that might be introduced by the use of a single method.
424. Lick slit spectra of quasar
ID:
ivo://CDS.VizieR/J/AJ/106/426
Title:
Lick slit spectra of quasar
Short Name:
J/AJ/106/426
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Lick Observatory slit spectra of 38 objects which were claimed to have pronounced ultraviolet excess and emission lines. Zhan & Chen (ZC) selected these objects by eye from a UK Schmidt telescope IIIaJ objective prism plate of a field at 0h 0.0deg (l ~= 98 deg, b ~= -60 deg). We concentrate on m(J) ~= 18-19 objects which Zhan and Chen (ZC) thought were most likely to be quasistellar objects (QSOs) at redshift z(em) >= 2.8. Most of our spectra have FWHM spectral resolutions of about 4 A, and relatively high S/N of about 10-50, although some have FWHM ~= 15 A or lower S/N. We find eleven QSOs, four galaxies at z ~= 0.1, twenty-two stars and one unidentified object with a low S/N spectrum. The ZC lists are found to contain many QSOs at low z but few at high z, as expected. Of eleven objects which ZC suggested were QSOs with z(prism) <= 2.8, eight (73%) are QSOs. But only three of twenty-five candidates with z(prism) >= 2.8 are QSOs, and only two (8%) of these are at z >= 2.8. Unfortunately, the ZC prism redshifts are often incorrect: only five of the eleven QSOs are at redshifts similar to z(prism). Six of the QSOs show absorption systems, including Q0000+027A with a relatively strong associated C IV absorption system, and Q0008+008 (V ~= 18.9) with a damped Ly alpha system with an HI column density of 10^21 cm^-2. The stars include a wide variety of spectral types. There is one new DA 4 white dwarf at 170 pc, one sdB at 14 kpc, and three M stars. The rest are of types F, G, and K. We have measured the equivalent widths of the Ca II K line, the G band, and the Balmer lines in ten stars with the best spectra, and we derive metallicities. Seven of them are in the range -2.5 <= [Fe/H] <= -1.7, while the others are less metal poor. If the stars are dwarfs, then they are at distances of 1 to 7 kpc, but if they are giants, typical distances will be about 10 kpc.
425. Light curves of 3C273 during 2015-2019
ID:
ivo://CDS.VizieR/J/A+A/636/A62
Title:
Light curves of 3C273 during 2015-2019
Short Name:
J/A+A/636/A62
Date:
21 Oct 2021
Publisher:
CDS
Description:
The powerful radiation over the entire electromagnetic spectrum and its radio jet activity of the blazar 3C 273 offer the opportunity of studying the physics of {gamma}-ray emission from active galactic nuclei. Since the historically strong outburst in 2009, 3C 273 showed relatively weak emission in the {gamma}-ray band over several years. However, recent Fermi-Large Area Telescope observations indicate higher activity during 2015-2019. We constrain the origin of the {gamma}-ray outbursts toward 3C 273 and investigate their connection to the parsec-scale jet. We generated Fermi-LAT {gamma}-ray light curves with multiple binning intervals and studied the spectral properties of the {gamma}-ray emission. Using a 3mm ALMA light curve, we studied the correlation between radio and {gamma}-ray emission. The relevant activity in the parsec-scale jet of 3C 273 was investigated with 7 mm VLBA observations that were obtained close in time to notable {gamma}-ray outbursts. We find two prominent {gamma}-ray outbursts in 2016 (MJD 57382) and 2017 (MJD 57883) accompanied by millimeter-wavelength flaring activity. The {gamma}-ray photon index time series show a weak hump-like feature around the {gamma}-ray outbursts. The monthly {gamma}-ray flux-index plot indicates a transition from softer-when-brighter to harder-when-brighter states at 1.03x10^-7^ph/cm^2^/s. A significant correlation between the {gamma}-ray and millimeter-wavelength emission is found, and the radio lags the {gamma}-rays by about 105-112 days. The 43GHz jet images reveal the known stationary features (i.e., the core, S1, and S2) in a region upstream of the jet. We find an indication for a propagating disturbance and a polarized knot between the stationary components at about the times of the two {gamma}-ray outbursts. Our results support a parsec-scale origin for the observed higher {gamma}-ray activity, which suggests that this is associated with standing shocks in the jet.
426. Light curves of the quasar He 0435-1223
ID:
ivo://CDS.VizieR/J/ApJ/789/125
Title:
Light curves of the quasar He 0435-1223
Short Name:
J/ApJ/789/125
Date:
21 Oct 2021
Publisher:
CDS
Description:
Microlensing has proved an effective probe of the structure of the innermost regions of quasars and an important test of accretion disk models. We present light curves of the lensed quasar HE 0435-1223 in the R band and in the ultraviolet (UV), and consider them together with X-ray light curves in two energy bands that are presented in a companion paper. Using a Bayesian Monte Carlo method, we constrain the size of the accretion disk in the rest-frame near- and far-UV, and constrain for the first time the size of the X-ray emission regions in two X-ray energy bands. The R-band scale size of the accretion disk is about 10^15.23^ cm (~23r_g_), slightly smaller than previous estimates, but larger than would be predicted from the quasar flux. In the UV, the source size is weakly constrained, with a strong prior dependence. The UV to R-band size ratio is consistent with the thin disk model prediction, with large error bars. In soft and hard X-rays, the source size is smaller than ~10^14.8^ cm (~10r_g_) at 95% confidence. We do not find evidence of structure in the X-ray emission region, as the most likely value for the ratio of the hard X-ray size to the soft X-ray size is unity. Finally, we find that the most likely value for the mean mass of stars in the lens galaxy is ~0.3 M_{sun}_, consistent with other studies.
427. Likelihood method for QSOs selection
ID:
ivo://CDS.VizieR/J/ApJ/743/125
Title:
Likelihood method for QSOs selection
Short Name:
J/ApJ/743/125
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new method for quasar target selection using photometric fluxes and a Bayesian probabilistic approach. For our purposes, we target quasars using Sloan Digital Sky Survey (SDSS) photometry to a magnitude limit of g=22. The efficiency and completeness of this technique are measured using the Baryon Oscillation Spectroscopic Survey (BOSS) data taken in 2010. This technique was used for the uniformly selected (CORE) sample of targets in BOSS year-one spectroscopy to be realized in the ninth SDSS data release. When targeting at a density of 40 objects deg^-2^ (the BOSS quasar targeting density), the efficiency of this technique in recovering z>2.2 quasars is 40%. The completeness compared to all quasars identified in BOSS data is 65%. This paper also describes possible extensions and improvements for this technique.
428. Linear polarization of AGN jets at 15GHz
ID:
ivo://CDS.VizieR/J/AJ/130/1389
Title:
Linear polarization of AGN jets at 15GHz
Short Name:
J/AJ/130/1389
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present first-epoch, milliarcsecond-scale linear polarization images at 15GHz of 133 jets associated with active galactic nuclei (AGNs) from the MOJAVE (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) survey. MOJAVE is a long-term observational program to study the structure and evolution of relativistic outflows in AGNs. The sample consists of all known AGNs with Galactic latitude |b|>2.5{deg}, J2000.0 declination greater than -20{deg} and correlated 15GHz Very Long Baseline Array (VLBA) flux density exceeding 1.5Jy (2Jy for sources below the celestial equator) at any epoch during the period 1994-2003.
429. List of extra-galactic radio jets
ID:
ivo://CDS.VizieR/J/A+A/381/757
Title:
List of extra-galactic radio jets
Short Name:
J/A+A/381/757
Date:
21 Oct 2021
Publisher:
CDS
Description:
Table 1 lists 661 radio sources with detected radio jets known to us prior to the end of December 2000
430. LOFAR images of blazar S5 0836+710
ID:
ivo://CDS.VizieR/J/A+A/631/A49
Title:
LOFAR images of blazar S5 0836+710
Short Name:
J/A+A/631/A49
Date:
21 Oct 2021
Publisher:
CDS
Description:
The emission and proper motion of the terminal hotspots of active galactic nucleus (AGN) jets can be used as a powerful probe of the intergalactic medium. However, measurements of hotspot advance speeds in active galaxies are difficult, especially in the young universe, because of the low angular velocities and the low brightness of distant radio galaxies. Our goal is to study the termination of an AGN jet in the young universe and to deduce physical parameters of the jet and the intergalactic medium. We used the LOw Frequency ARray (LOFAR) to image the long-wavelength radio emission of the high-redshift blazar S5 0836+710 on arcsecond scales between 120MHz and 160MHz. The LOFAR image shows a compact unresolved core and a resolved emission region about 1.5 arcsec to the southwest of the radio core. This structure is in general agreement with previous higher-frequency radio observations with the Multi-Element Radio-Linked Interferometer Network (MERLIN) and the Very Large Array (VLA). The southern component shows a moderately steep spectrum with a spectral index of about >~-1,and the spectral index of the core is flat to slightly inverted. In addition, we detect for the first time a resolved steep-spectrum halo with a spectral index of about -1 surrounding the core. The arcsecond-scale radio structure of S5 0836+710 can be understood as a Faranoff-Riley (FR) II radio galaxy observed at a small viewing angle. The southern component can be interpreted as the region of the approaching jet's terminal hotspot, and the halo like diffuse component near the core can be interpreted as the counter-hotspot region. From the differentialDoppler boosting of both features, we can derive the hotspot advance speed to (0.01-0.036)c. Ata constant advance speed, the derived age of the source would exceed the total lifetime of such a powerful FR II radio galaxy substantially. Thus, the hotspot advance speed must have been higher in the past, in agreement with a scenario in which the originally highly relativistic jet has lost collimation as a result of instability growth and has transformed into an only mildly relativistic flow. Our data suggest that the density of the intergalactic medium around this distant (z=2.22) AGN could be substantially higher than the values typically found in less distant FR II radio galaxies.