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1. A catalogue of BL Lacertae objects
ID:
ivo://CDS.VizieR/J/MNRAS/277/1477
Title:
A catalogue of BL Lacertae objects
Short Name:
J/MNRAS/277/1477
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalogue of 233 BL Lacertae objects compiled through an extensive bibliographic search updated to mid-1995. A large fraction of the sources listed in the catalogue belongs to well-defined samples and can be used for statistical purposes. A smaller fraction consists of miscellaneous (but confirmed) BL Lacs and of objects classified as BL Lac candidates. We discuss the selection criteria of the different samples, report the discovery of two previously unnoticed BL Lacs in the Palomar-Green survey, and comment on the possible association of some of the still unidentified high galactic latitude gamma-ray (EGRET, see Thompson et al., =1995ApJS..101..259T) sources with BL Lacs. Some statistical properties of the catalogue are also briefly discussed.
2. AGN jet kinematics
ID:
ivo://CDS.VizieR/J/AJ/130/1418
Title:
AGN jet kinematics
Short Name:
J/AJ/130/1418
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present total and polarized intensity images of 15 active galactic nuclei obtained with the Very Long Baseline Array at 7mm (43GHz) wavelength at 17 epochs from 1998 March to 2001 April. At some epochs the images are accompanied by nearly simultaneous polarization measurements at 3mm (86GHz) with the Berkeley-Illinois-Maryland Association (BIMA) array (Hat Creek, California), 1.35/0.85mm (230/350GHz) with the James Clerk Maxwell Telescope (JCMT; using SCUBA and its polarimeter, and at the Steward Observatory 1.5m telescope (Mount Lemmon, Arizona) with the Two-Holer Polarimeter/Photometer over an effective wavelength range of ~6000-7000{AA}. Here we analyze the 7mm images to define the properties of the jets of two radio galaxies, five BL Lac objects, and eight quasars on angular scales >~0.1mas. We determine the apparent velocities of 106 features in the jets.
3. A 3.5mm polarimetric survey of radio-loud AGNs
ID:
ivo://CDS.VizieR/J/ApJS/189/1
Title:
A 3.5mm polarimetric survey of radio-loud AGNs
Short Name:
J/ApJS/189/1
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results from the first large (>100 sources) 3.5mm polarimetric survey of radio-loud active galactic nuclei (AGNs). This wavelength is favorable within the radio-millimeter range for measuring the intrinsic linearly polarized emission from AGNs, since in general it is only marginally affected by Faraday rotation of the electric vector position angle and depolarization. The I, Q, U, and V Stokes parameter observations were performed with the XPOL polarimeter at the IRAM 30m Telescope on different observing epochs from 2005 July (when most of the measurements were made) to 2009 October. Our sample consists of 145 flat-radio-spectrum AGNs with declination >-30{deg} (J2000.0) and flux density >~1Jy at ~86GHz, as measured at the IRAM 30m Telescope from 1978 to 1994. This constraint on the radio spectrum causes our sample to be dominated by blazars, which allows us to conduct new statistical studies on this class of high-luminosity, relativistically beamed emitters. Over our entire source sample, the luminosity of the jets is anticorrelated with the degree of linear polarization. Consistent with previous findings claiming larger Doppler factors for brighter {gamma}-ray blazars, quasars listed in our sample, and in the Fermi Large Area Telescope Bright Source Catalog (LBAS, Abdo et al., 2009ApJ...700..597A), show larger luminosities than non-LBAS ones, but our data do not allow us to confirm the same for BL Lac objects. Our new data can be used to estimate the 3.5mm AGN contribution to measurements of the linear polarization of the cosmic microwave background, such as those performed by the Planck satellite.
4. An optical overview of blazars with LAMOST. I.
ID:
ivo://CDS.VizieR/J/AJ/161/196
Title:
An optical overview of blazars with LAMOST. I.
Short Name:
J/AJ/161/196
Date:
16 Mar 2022 11:51:00
Publisher:
CDS
Description:
The extragalactic {gamma}-rays sky observed by the Fermi Large Area Telescope (LAT) is dominated by blazars. In the fourth release of the Fermi LAT Point Source Catalog (4FGL) are sources showing a multifrequency behavior similar to that of blazars but lacking an optical spectroscopic confirmation of their nature, known as blazar candidates of uncertain type (BCUs). We aim at confirming the blazar nature of BCUs and test if new optical spectroscopic observations can reveal spectral features, allowing us to get a redshift estimate for known BL Lac objects. We also aim to search for and discover changing-look blazars (i.e., blazars that show a different classification at different epochs). We carry out an extensive search for optical spectra available in the Large Sky Area Multi-object Fibre Spectroscopic Telescope (LAMOST) Data Release 5 (DR5) archive. We select sources out of the 4FGL catalog, the list of targets from our follow-up spectroscopic campaign of unidentified or unassociated {gamma}-ray sources, and the multifrequency catalog of blazars: the Roma-BZCAT. We select a total of 392 spectra. We also compare some of the LAMOST spectra with those available in the literature. We classify 20 BCUs confirming their blazar-like nature. Then we obtain 15 new redshift estimates for known blazars. We discover 26 transitional (i.e., changing-look) blazars that changed their classification. Finally, we are able to confirm the blazar-like nature of six BL Lac candidates. All remaining sources analyzed agree with previous classifications. BL Lac objects are certainly the most elusive type of blazars in the {gamma}-ray extragalactic sky.
5. AO 0235+164 BVRI photometry
ID:
ivo://CDS.VizieR/J/A+AS/129/577
Title:
AO 0235+164 BVRI photometry
Short Name:
J/A+AS/129/577
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of the optical and radio monitoring of the BL Lac object AO 0235+164 during a faint state. In both optical and radio bands the source has been observed at the faintest ever recorded levels, reaching V=19.80 and F_22GHz_=0.34Jy. In the optical bands we still see variability with amplitudes up to 1.5 magnitudes on timescales from days to weeks. The radio variability is less dramatic, but in general follows the optical behaviour. A correlation between general trends in the optical and radio behaviour of AO 0235+164 may be recognized in the data from the present monitoring as well as in the historical light curves, suggesting a `base' mechanism responsible for the emission at both frequencies. A good candidate is a synchrotron process in the relativistic jet. Optical flares with no corresponding radio counterparts have been observed too. These events may be interpreted in terms of microlensing by a foreground galaxy.
6. AO 0235+164 outburst in 2006 December
ID:
ivo://CDS.VizieR/J/ApJ/672/40
Title:
AO 0235+164 outburst in 2006 December
Short Name:
J/ApJ/672/40
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of polarimetric (R-band) and multicolor photometric (BVRIJHK) observations of the blazar AO 0235+16 during an outburst in 2006 December. The data reveal a short timescale of variability (several hours), which increases from optical to near-IR wavelengths; even shorter variations are detected in polarization. The flux density correlates with the degree of polarization, and at the maximum degree of polarization the electric vector tends to align with the parsec-scale jet direction. We find that a variable component with a steady power-law spectral energy distribution and very high optical polarization (30%-50%) is responsible for the variability. We interpret these properties of the blazar within a model of a transverse shock propagating down the jet. In this case a small change in the viewing angle of the jet, by ~<1{deg}, and a decrease in the shocked plasma compression by a factor of ~1.5 are sufficient to account for the variability.
7. BATC ceimo light curves of 1ES 0806+52.4
ID:
ivo://CDS.VizieR/J/AJ/148/110
Title:
BATC ceimo light curves of 1ES 0806+52.4
Short Name:
J/AJ/148/110
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of the first systematic long-term multicolor optical monitoring of the BL Lacertae object 1ES 0806+52.4. The monitoring was performed in multiple passbands with a 60/90cm Schmidt telescope from 2005 December to 2011 February. The overall brightness of this object decreased from 2005 December to 2008 December but was regained after that. A sharp outburst probably occurred around the end of our monitoring program. Overlapping the long-term trend are some short-term small-amplitude oscillations. No intranight variability was found in the object, which is in accordance with the historical observations before 2005. By investigating the color behavior, we found a strong bluer-when-brighter chromatism for the long-term variability of 1ES 0806+52.4. The total amplitudes at the c, i, and o bands are 1.18, 1.12, and 1.02mag, respectively. The amplitudes tend to increase toward shorter wavelengths, which may be a major cause of the bluer-when-brighter chromatism. Such bluer-when-brighter chromatisms are also found in other blazars, such as S5 0716+714, OJ 287. The hard-X-ray data collected from the Swift/BAT archive was correlated with our optical data. No positive result was found, the reason for which may be that the hard-X-ray flux is a combination of the synchrotron and inverse Compton emission, but with different timescales and cadences under the leptonic synchrotron self-Compton model.
8. BATC ceimo light curves of OJ 287
ID:
ivo://CDS.VizieR/J/AJ/141/65
Title:
BATC ceimo light curves of OJ 287
Short Name:
J/AJ/141/65
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper studies the color behavior of the BL Lac object OJ 287 during an optical outburst. Upon revisiting the data from the OJ 94 monitoring project, and from an analysis of the data obtained with the 60/90cm Schmidt Telescope of NAOC, we found a bluer-when-brighter chromatism in this object. The amplitude of variation tends to decrease with frequency. These results are consistent with the shock-in-jet model. We ran some simulations and confirmed that both amplitude difference and time delay between variations at different wavelengths can result in the bluer-when-brighter phenomenon. Our observations confirmed that OJ 287 underwent a double-peaked outburst about 12 years after 1996, which provides further evidence for the binary black hole model in this object.
9. BATC eim photometry of BL Lac
ID:
ivo://CDS.VizieR/J/MNRAS/373/209
Title:
BATC eim photometry of BL Lac
Short Name:
J/MNRAS/373/209
Date:
21 Oct 2021
Publisher:
CDS
Description:
The aim of our observations is to investigate the intra-night variability properties and the spectral variability of BL Lacertae. 799 optical multiband observations were intensively made with the Beijing-Arizona-Taiwan-Connecticut (BATC) 60/90cm Schmidt telescope during the outburst composed of two subsequent flares in 2005. The second flare, whose rising phase lasted at least 44d, was observed with amplitudes of more than 1.1mag in three BATC optical bands. In general, on intra-night time-scale the amplitude of variability and the variation rate are larger at the shorter wavelength, and the variation rate is comparable in the rising and decaying phases within each band. A possible time-lag between the light curves in bands e and m, around 11.6min, was obtained. Based on the analysis of the colour index variation with the source brightness, the variability of BL Lacertae can be interpreted as having two components: a 'strongly chromatic' intra-night component and a 'mildly chromatic' inter-night component, which may be the results of both intrinsic physical mechanism and geometric effects.
10. Bimodal radio variability in OVRO blazars
ID:
ivo://CDS.VizieR/J/MNRAS/467/4565
Title:
Bimodal radio variability in OVRO blazars
Short Name:
J/MNRAS/467/4565
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blazars are known to show periods of quiescence followed by outbursts visible throughout the electromagnetic spectrum. We present a novel maximum likelihood approach to capturing this bimodal behavior by examining blazar radio variability in the flux-density domain. We separate quiescent and flaring components of a source's light curve by modeling its flux-density distribution as a series of "off" and "on" states. Our modeling allows us to extract information regarding the flaring ratio, duty cycle, and the modulation index in the "off"-state, in the "on"-state, as well as throughout the monitoring period of each blazar. We apply our method to a flux-density-limited subsample from the Owens Valley Radio observatory's 15 GHz blazar monitoring program, and explore differences in the variability characteristics between BL Lacs and FSRQs as well as between {gamma}-ray detected and non-detected sources. We find that: (1) BL Lacs are more variable and have relatively larger outbursts than the FSRQs; (2) unclassified blazar candidates in our sample show similar variability characteristics as the FSRQs; and (3) {gamma}-ray detected differ from the {gamma}-ray non-detected sources in all their variability properties, suggesting a link between the production of {gamma}-rays and the mechanism responsible for the radio variability. Finally, we fit distributions for blazar flaring ratios, duty cycles, and on- and off- modulation indices that can be used in population studies of variability-dependent blazar properties.

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