Search

Start Over Subject quasars
591. 2001-02 optical variability of blazar 3C 279
ID:
ivo://CDS.VizieR/J/AJ/133/2866
Title:
2001-02 optical variability of blazar 3C 279
Short Name:
J/AJ/133/2866
Date:
21 Oct 2021
Publisher:
CDS
Description:
During 2001-2002 the optically violent variable blazar 3C 279 underwent the most intense outburst seen during the entire 14yr period that this quasar has been studied at Colgate University's Foggy Bottom Observatory. This study concentrates on ~1600 R-filter images taken during this period of activity. This data set includes 29 nights of microvariability coverage. The outburst began in 2001 March, after 3C 279 had faded to its faintest level, R=15.5, in 4yr. The source reached its brightest level, R=12.5, in the 14yr of our study in 2001 August, at which time it became unobservable due to its proximity to the Sun. On becoming observable again in 2001 mid-December, 3C 279 fluctuated between R=13.9 and 14.7, until a dramatic decrease in flux level in 2002 June-July brought the source back down to a level comparable to its preoutburst state. The source exhibited numerous week-long flares of approximately 1mag during the outburst period. Superposed on these flares were night-to-night variations of up to 0.5mag and intranight microvariability of up to 0.13mag in 3hr. We use visual inspection of the light curve, as well as numerical timescale analysis tools (the autocorrelation function, the structure function, and the power spectrum), to characterize the multiple timescales of variability ranging from 1.5yr to several hours.
592. Optical variability of blazars
ID:
ivo://CDS.VizieR/J/AN/340/437
Title:
Optical variability of blazars
Short Name:
J/AN/340/437
Date:
21 Oct 2021
Publisher:
CDS
Description:
The analysis of blazars' parameters from BZCAT leads to a conclusion that they do not have the same properties. The preliminary criterion to include an object in the catalog was the strong radio emission; however, two type of radio sources were selected: BL Lacertae (BLL) objects and Flat Spectrum Radio Quasars (FSRQ). As a number of properties are typical of blazars (strong radio emission, optical variability, continuum optical spectra, polarization, high luminosity, etc.), using the optical data, we investigate them to clarify which property plays the most significant role in their classification as blazars. We found that 60% of blazars have optical variability. We use a technique developed based on POSS1 and POSS2 photometry and group the variability into extreme, strong, medium, and low classes. In the optical range, 51 blazars have powerful variability (extreme variables), and 126 are high variables. In addition, 63% of blazars have detected radiation in X-ray and 28% have detected radiation in gamma rays. We give the average statistical characteristics of blazars based on our analysis and calculations.
593. Optical variability of QSOs
ID:
ivo://CDS.VizieR/J/A+A/321/123
Title:
Optical variability of QSOs
Short Name:
J/A+A/321/123
Date:
21 Oct 2021
Publisher:
CDS
Description:
The SA94 variability sample is made up of 149 optically selected quasars listed in this table, observed in a rectangular area of the sky within the limits 2h 43m 51.2s < RA < 2h 59m 14.3s, -2deg 03' 23.8" < DEC < 2deg 32' 11.0" (Epoch 1950.0), covering 17.66 sq.deg.
594. Opt-IR LC compilation of DES Stripe 82 quasars
ID:
ivo://CDS.VizieR/J/ApJ/900/58
Title:
Opt-IR LC compilation of DES Stripe 82 quasars
Short Name:
J/ApJ/900/58
Date:
11 Mar 2022 15:16:31
Publisher:
CDS
Description:
The size of the dust torus in active galactic nuclei (AGNs) and their high-luminosity counterparts, quasars, can be inferred from the time delay between UV/optical accretion disk continuum variability and the response in the mid-infrared (MIR) torus emission. This dust reverberation mapping (RM) technique has been successfully applied to ~70 z<~0.3 AGNs and quasars. Here we present first results of our dust RM program for distant quasars covered in the Sloan Digital Sky Survey Stripe 82 region combining ~20yr ground-based optical light curves with 10yr MIR light curves from the WISE satellite. We measure a high-fidelity lag between W1 band (3.4{mu}m) and g band for 587 quasars over 0.3<~z<~2 (<z>~0.8) and two orders of magnitude in quasar luminosity. They tightly follow (intrinsic scatter ~0.17dex in lag) the IR lag-luminosity relation observed for z<0.3 AGNs, revealing a remarkable size-luminosity relation for the dust torus over more than four decades in AGN luminosity, with little dependence on additional quasar properties such as Eddington ratio and variability amplitude. This study motivates further investigations in the utility of dust RM for cosmology and strongly endorses a compelling science case for the combined 10yr Vera C. Rubin Observatory Legacy Survey of Space and Time (optical) and 5yr Nancy Grace Roman Space Telescope 2{mu}m light curves in a deep survey for low-redshift AGN dust RM with much lower luminosities and shorter, measurable IR lags. The compiled optical and MIR light curves for 7384 quasars in our parent sample are made public with this work.
595. Opt-NIR light curve of the quasar 3C 273
ID:
ivo://CDS.VizieR/J/AJ/159/259
Title:
Opt-NIR light curve of the quasar 3C 273
Short Name:
J/AJ/159/259
Date:
21 Oct 2021
Publisher:
CDS
Description:
We monitored the z=0.158 quasar 3C273 between 2015 and 2019 in the optical (BVrz) and near-infrared (JHK) with the aim to perform dust reverberation mapping. Accounting for host galaxy and accretion disk contributions, we obtained pure dust light curves in JHK. Cross correlations between the V-band and the dust light curves yield an average rest-frame delay for the hot dust of {tau}cent~410days. This is a factor of two shorter than that expected from the the dust ring radius R_x_~900lt-day reported from interferometric studies. The dust covering factor (CF) is about 8%, much smaller than that predicted from the half covering angle of 45{deg} found for active galactic nuclei (AGNs). We analyze the asymmetric shape of the correlation functions and explore whether an inclined biconical bowl-shaped dust torus geometry could bring these findings ({tau}cent, Rx and CF) into a consistent picture. The hot varying dust emission originates from the edge of the bowl rim with a small covering angle 40{deg}<{theta}<45{deg}, and we see only the near side of the biconus. Such a dust gloriole with R_x_= 900{+/-}200lt-day and an inclination 12{deg} matches the data remarkably well. Comparing the results of 3C273 with literature for less luminous AGN, we find a lag-luminosity relation {tau}{prop}L{alpha} with {alpha}=0.33-0.40, flatter than the widely adopted relation with {alpha}~0.5. We address several explanations for the new lag-luminosity relation.
596. Orientation & QSO black hole mass estimation
ID:
ivo://CDS.VizieR/J/MNRAS/454/3864
Title:
Orientation & QSO black hole mass estimation
Short Name:
J/MNRAS/454/3864
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have constructed a sample of 386 radio-loud quasars with z<0.75 from the Sloan Digital Sky Survey in order to investigate orientation effects on black hole mass estimates. Orientation is estimated using radio core dominance measurements based on FIRST survey maps. Black hole masses are estimated from virial-based scaling relationships using H{beta}, and compared to the stellar velocity dispersion ({sigma}*), predicted using the full width at half maximum (FWHM) of [OIII] {lambda}5007, which tracks mass via the M-{sigma}* relation. We find that the FWHM of H{beta} correlates significantly with radio core dominance and biases black hole mass determinations that use it, but that this is not the case for {sigma}* based on [OIII] {lambda}5007. The ratio of black hole masses predicted using orientation-biased and unbiased estimates, which can be determined for radio-quiet as well as radio-loud quasars, is significantly correlated with radio core dominance. Although there is significant scatter, this mass ratio calculated in this way may in fact serve as an orientation estimator. We additionally note the existence of a small population of radio core-dominated quasars with extremely broad H{beta} emission lines that we hypothesize may represent recent black hole mergers.
597. Pairs of QSO in SDSS-DR4
ID:
ivo://CDS.VizieR/J/ApJ/658/99
Title:
Pairs of QSO in SDSS-DR4
Short Name:
J/ApJ/658/99
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study quasar clustering on small scales, modeling clustering amplitudes using halo-driven dark matter descriptions. From 91 pairs n scales <35h^-1^kpc, we detect only a slight excess in quasar clustering over our best-fit large-scale model. Integrated across all redshifts, the implied quasar bias is bQ=4.21+/-0.98 (bQ=3.93+/-0.71) at ~18h^-1^kpc (~28h^-1^kpc).
598. PanSTARRS-1 slow-blue nuclear hypervariables
ID:
ivo://CDS.VizieR/J/MNRAS/463/296
Title:
PanSTARRS-1 slow-blue nuclear hypervariables
Short Name:
J/MNRAS/463/296
Date:
21 Oct 2021
Publisher:
CDS
Description:
We discuss 76 large amplitude transients ({Delta}m>1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN). They have been discovered as part of the Pan-STARRS1 (PS1) 3{pi} survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. A few are either radio sources or erratic variables and so likely blazars. However the majority (~66 per cent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at z ~0.3-1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as 'hypervariable' AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanations for these slow-blue hypervariables - (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. Both hold promise of considerable new insight into the AGN phenomenon.
599. Parkes Quarter-Jansky Flat-Spectrum Sample. II.
ID:
ivo://CDS.VizieR/J/A+A/399/469
Title:
Parkes Quarter-Jansky Flat-Spectrum Sample. II.
Short Name:
J/A+A/399/469
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present optical spectra and redshift measurements for 178 flat-spectrum objects from the Parkes quarter-Jansky flat-spectrum sample. These spectra were obtained in order to compile a complete sample of quasars for use in a study of quasar evolution. We present a composite optical spectrum made from the subset of 109 quasars that have flux densities in the range 0.25Jy<S(2.7GHz)<0.5Jy, and make a comparison with a composite spectrum for radio-quiet QSOs from the Large Bright Quasar Survey. Our large sample of radio-loud quasars allows us to strengthen previous reports that the Ly and CIV emission lines have larger equivalent width in radio-loud quasars than radio-quiet QSOs to greater than the 3{sigma} level. However we see no significant difference in the equivalent widths of CIII] or MgII. We also show that the flux decrements across the Lyman-{alpha} line (DA) measured from these spectra show the same trend with redshift as for optically selected QSOs.
600. PG 2130+099 narrowband light curves
ID:
ivo://CDS.VizieR/J/A+A/659/A13
Title:
PG 2130+099 narrowband light curves
Short Name:
J/A+A/659/A13
Date:
25 Feb 2022 07:32:33
Publisher:
CDS
Description:
We present the results of an intensive six-month optical continuum reverberation mapping campaign of the Seyfert 1 galaxy PG 2130+099 at redshift z=0.063. The ground- based photometric monitoring was conducted on a daily basis with the robotic 46cm telescope of the Wise observatory located in Israel. Specially designed narrowband filters were used to observe the central engine of the active galactic nucleus (AGN), avoiding line contamination from the broad-line region (BLR). We aim to measure inter- band continuum time lags across the optical range and determine the size-wavelength relation for this system. PG 2130+099 displays correlated variability across the optical range, and we successfully detect significant time lags of up to 3 days between the multiband light curves. While a continuum reprocessing model can fit the data reasonably well, our derived disk sizes are a factor of 2-6 larger than the theoretical disk sizes predicted from the AGN luminosity estimate of PG 2130+099. This result is in agreement with previous studies of AGN/quasars and suggests that the standard Shakura- Sunyaev disk theory has limitations in describing AGN accretion disks.