Long-term photometry of blazars at Abastumani Observatory

The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected between 100 MeV and 300 GeV with a Test Statistic greater than 25, between 2008 August 4 and 2012 July 31. The 3LAC includes 1591 AGNs located at high Galactic latitudes (>  | | b 10), a 71% increase over the second catalog based on 2 years of data. There are 28 duplicate associations, thus 1563 of the 2192 high-latitude gamma-ray sources of the 3FGL catalog are AGNs. Most of them (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Based on their gamma-ray spectral properties, these sources are evenly split between flat-spectrum radio quasars (FSRQs) and BL Lacs. The most abundant detected BL Lacs are of the high-synchrotron-peaked (HSP) type. About 50% of the BL Lacs have no measured redshifts. A few new rare outliers (HSP-FSRQs and high-luminosity HSP BL Lacs) are reported. The general properties of the 3LAC sample confirm previous findings from earlier catalogs. The fraction of 3LAC blazars in the total population of blazars listed in BZCAT remains non-negligible even at the faint ends of the BZCAT-blazar radio, optical, and X-ray flux distributions, which hints that even the faintest known blazars could eventually shine in gamma-rays at LAT-detection levels. The energy-flux distributions of the different blazar populations are in good agreement with extrapolation from earlier catalogs.

Astrophysics, 2008

We present results of CCD BVRI observations of comparison stars in the fields of 44 active galactic nuclei, mainly Seyfert galaxies. These results can be used for differential photometry of AGNs in B, V , R c ,andI c bands. The photometric uncertainties are typically 0.003 -0.010 mag.

Astronomy Reports, 2004

VLBI observations of several quasars and BL Lacertae objects were carried out at 1.66 GHz in November-December 1999 using six antennas (Medvezh'i Ozera, Svetloe, Pushchino, Noto, Har-tRAO, and Shanghai). Maps of six sources (0420+022, 0420−014, 1308+326, 1345+125, 1803+784, and DA 193) obtained with milliarcsecond resolution are presented and discussed, together with their broadband (1-22 GHz) spectra obtained on the RATAN-600 radio telescope at epochs close to those of the VLBI observations. Comparison of the VLBI maps with maps of these sources obtained on standard VLBI networks and with the RATAN-600 quasi-simultaneous total-flux measurements indicates the reliability of the results obtained on this Low Frequency VLBI Network and the good efficiency of this network.

The Astrophysical Journal

The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains 2863 objects located at high Galactic latitudes (| | >  b 10). It includes 85% more sources than the previous 3LAC catalog based on 4 yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50 MeV to 1 TeV. In addition, 344 gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BLLacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.

Astrophysics and Space Science, 2016

Despite the fact that blazars constitute the rarest class among active galactic nuclei (AGNs) they are the largest known population of associated γ-ray sources. Many of the γ-ray objects listed in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs), either because they show multifrequency behaviour similar to blazars but lacking optical spectra in the literature, or because the quality of such spectra is too low to confirm their nature. Here we select, out of 585 BCUs in the 3FGL, 42 BCUs which we identify as probable blazars by their WISE infrared colors and which also have optical spectra that are available in the Sloan Digital Sky Survey (SDSS) and/or Six-Degree Field Galaxy Survey Database (6dFGS). We confirm the blazar nature of all of the sources. We furthermore conclude that 28 of them are BL Lacs, 8 are radio-loud quasars with flat radio spectrum and 6 are BL Lac whose emission is dominated by their host galaxy.

Proceedings of 3rd Annual Conference on High Energy Astrophysics in Southern Africa — PoS(HEASA2015), 2016

BL Lacartae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) exhibit variability in the continuum flux at multiple wavelengths on timescales of hours to days. We report on optical photometric observations of 8 unidentified Active Galactic Nuclei (AGN) from the second Fermi-LAT catalogue of AGN, that shows potential blazar characteristics. We mainly focus our attention on the intra-day variability (IDV) with timescales of a few minutes to within a day and the short term variability (STV) on timescales of a few days to months. Variability on these timescales are known to be the result of the shock zones within the jet, hot spots and/or instabilities in the accretion disk. Preliminary differential photometric results, for the 8 target sources, obtained with the SAAO 1.9-m Sutherland High-Speed Optical Camera (SHOC) during December 2014 and May 2015, are discussed. Currently, optical long term monitoring of the entire target sample using the Watcher Robotic Telescope is undertaken to determine magnitudes in the RVi filters, as well as radio observations with the the HartRAO 26-m radio telescope to construct light curves in order to study the variability.

2000

The high redshift (z =0 :997) blazar B2 1308+326 was observed contemporaneously at x-ray, optical and radio wavelengths in June 1996. The x-ray observations were per- formed with ASCA. The ASCA results were found to be con- sistent with reanalysed data from two earlier ROSAT obser- vations. The combined ASCA and ROSAT data reveal an x- ray spectrum that is

2008

We report here the first results of a long term optical (V, R) monitoring program of blazars that includes 3 well-known objects: 3C279 (1253-055), CTA102 (2230+114) and 3C454.3 (2251+158). The observations were obtained with the 1.52m Spanish telescope at the Calar Alto Observatory during 2006-2007. Although no significant intra-night variations were detected in any of the objects, we found inter-day

The Astrophysical Journal, 2009

The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at |b| > 10 • with test statistic greater than 100 (corresponding to about 10σ ). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at |b| < 10 • , were previously detected with Energetic Gamma-Ray Experiment Telescope(EGRET), probably due to variability. The analysis of the γ -ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak γ -ray fluxes is observed. Blazar log N -log S distributions and luminosity functions are constructed to investigate the evolution of the different blazar classes, with positive evolution indicated for FSRQs but none for BL Lacs. The contribution of LAT blazars to the total extragalactic γ -ray intensity is estimated.