scholarly journals A CCD survey of BL Lac objects

1986 ◽  
Vol 119 ◽  
pp. 125-126
Author(s):  
Helmut Kuhr ◽  
Josef Fried
Keyword(s):  
Optical Spectroscopy ◽  
Max Planck ◽  
Complete Sample ◽  
Bl Lac Objects ◽  
Ccd Imaging ◽  
Bl Lac ◽  
5 Ghz ◽  
Spectroscopy Optical

A long term project was started at the Max-Planck-Institut fur Astronomie, Heidelberg, to study a complete sample of 46 northern and southern BL Lac objects with flux densities exceeding 1 Jy at 5 GHz using optical spectroscopy, optical polarimetry, and direct deep CCD imaging.

scholarly journals Spatial Structures of a Complete Sample of Extragalactic Radio Sources North of Declination 70°

1984 ◽  
Vol 110 ◽  
pp. 65-66
Author(s):  
A. Eckart ◽  
A. Witzel
Keyword(s):  
Optical Spectroscopy ◽  
Radio Sources ◽  
Spatial Structures ◽  
Complete Sample ◽  
X Ray ◽  
Extragalactic Radio Sources ◽  
Bl Lac ◽  
5 Ghz

With the aim of studying the spatial structures of a complete sample of radio sources found at 6 cm wavelength we selected 13 sources from the “S5–survey” (Kühr et al., 1981) which fulfil the following criteria1) δ > 70°, |bII| > 10°2) S5 GHz > 1 Jy (at the epoch of the S5–survey)3) α5 GHz2.7 GHz > − 1.5 (S ∝ να)6 of these sources are identified by means of optical spectroscopy with QSOs, 6 are BL Lac-type objects, and the identification of 1 source is presently unknown. Observations at frequencies ranging from radio to X-ray have been reported (Biermann et al., 1981; Biermann et al., 1982; Eckart et al., 1982).

scholarly journals Characterizing the γ-ray long-term variability of PKS 2155−304 with H.E.S.S. and Fermi-LAT

2017 ◽  
Vol 598 ◽  
pp. A39 ◽  
Author(s):  
◽  
H. Abdalla ◽  
A. Abramowski ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
...  
Keyword(s):  
Flicker Noise ◽  
High Energy ◽  
Long Term Results ◽  
Noise Power ◽  
Quiescent State ◽  
Physical Processes ◽  
Bl Lac Objects ◽  
Power Spectral ◽  
Bl Lac

Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability of the BL Lac object PKS 2155−304 is analyzed in the high (HE, 100 MeV < E < 300 GeV) and very high energy (VHE, E > 200 GeV) γ-ray domain. Over the course of ~9 yr of H.E.S.S. observations the VHE light curve in the quiescent state is consistent with a log-normal behavior. The VHE variability in this state is well described by flicker noise (power-spectral-density index βVHE = 1.10+0.10-0.13) on timescales larger than one day. An analysis of ~5.5 yr of HE Fermi-LAT data gives consistent results (βHE = 1.20+0.21-0.23, on timescales larger than 10 days) compatible with the VHE findings. The HE and VHE power spectral densities show a scale invariance across the probed time ranges. A direct linear correlation between the VHE and HE fluxes could neither be excluded nor firmly established. These long-term-variability properties are discussed and compared to the red noise behavior (β ~ 2) seen on shorter timescales during VHE-flaring states. The difference in power spectral noise behavior at VHE energies during quiescent and flaring states provides evidence that these states are influenced by different physical processes, while the compatibility of the HE and VHE long-term results is suggestive of a common physical link as it might be introduced by an underlying jet-disk connection.

VERITAS OBSERVATIONS OF RELATIVISTIC OUTFLOWS IN LOW- AND INTERMEDIATE-FREQUENCY-PEAKED BL LAC OBJECTS

2014 ◽  
Vol 28 ◽  
pp. 1460178
Author(s):  
◽  
HEIKE PROKOPH
Keyword(s):  
Gamma Ray ◽  
Intermediate Frequency ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Bl Lacs ◽  
Gamma Ray Telescopes ◽  
Very High

The majority of blazars detected at very high energies (VHE; E > 100 GeV) are high-frequency-peaked BL Lac objects (HBLs). Low- and intermediate-frequency-peaked BL Lacs (LBLs/IBLs with synchrotron-peak frequencies in the infrared and optical regime) are generally more powerful, more luminous, and have a richer jet environment than HBLs. However, only a handful of these IBL and LBLs have been detected by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array has been monitoring five known VHE LBLs/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with typical exposures of 5-10 hours per year. The results of these long-term observations are presented, including a bright, subhour-scale VHE flare of BL Lacertae in June 2011, the first low-state detections of 3C 66A and W Comae, and the detection and characterization of the IBL B2 1215+30.

scholarly journals Frequency Dependence of the Parsec-scale Polarization Structures of BL Lac Objects

2001 ◽  
Vol 205 ◽  
pp. 140-141
Author(s):  
A.B. Pushkarev ◽  
D.C. Gabuzda ◽  
T.V. Cawthorne
Keyword(s):  
Line Emission ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Sky Survey ◽  
Radiation Sources ◽  
Wide Wavelength Range ◽  
Bl Lac ◽  
5 Ghz

BL Lacertae objects are active galactic nuclei with weak or undetectable line emission and strong variability in total intensity and linear polarization over a wide wavelength range from optical to radio. The radio emission and much of the optical emission is believed to be synchrotron radiation. Sources in the complete sample of BL Lac objects defined by Kühr and Schmidt (1990) have: 5 GHz fluxes of at least 1 Jy, radio spectral index α ≥ −0.5 (Sv ˜ v+α), rest frame equivalent width of the strongest emission lines less than 5 Å, and optical counterparts on the Sky Survey plates with brightness greater than 20m.

scholarly journals Long term γ-ray variability of blazars

2020 ◽  
Vol 634 ◽  
pp. A80 ◽  
Author(s):  
Bhoomika Rajput ◽  
C. S. Stalin ◽  
Suvendu Rakshit
Keyword(s):  
Time Scales ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Spectral Energy ◽  
Bl Lac Objects ◽  
Spectrum Radio ◽  
Bl Lac ◽  
Bl Lacs

We used the data from the Fermi Gamma-ray Space Telescope to characterise the γ-ray flux variability of blazars on month-like time scales. Our sample consists of 1120 blazars of which 481 are flat spectrum radio quasars (FSRQs) and 639 are BL Lac objects (BL Lacs). We generated monthly binned light curves of our sample for a period of approximately nine years from 2008 August to 2017 December and quantified variability by using excess variance (Fvar). On month-like time scales, 371/481 FSRQs are variable (80%), while only about 50% (304/639) of BL Lacs are variable. This suggests that FSRQs are more variable than BL Lac objects. We find a mean Fvar of 0.55 ± 0.33 and 0.47 ± 0.29 for FSRQs and BL Lacs respectively. Large Fvar in FSRQs is also confirmed from the analysis of the ensemble structure function. By Dividing our sample of blazars based on the position of the synchrotron peak in their broad-band spectral energy distribution, we find that the low synchrotron peaked (LSP) sources have the largest mean Fvar value of 0.54 ± 0.32 while the intermediate synchrotron peaked (ISP) and high synchrotron peaked sources have mean Fvar values of 0.45 ± 0.25 and 0.47 ± 0.33 respectively. On month-like time scales, we find FSRQs to show a high duty cycle (DC) of variability of 66% relative to BL Lacs that show a DC of 36%. We find that both the Fvar and time scale of variability (τ) do not correlate with MBH. We note that Fvar is found to be weakly correlated with Doppler factor (δ) and τ is also weakly correlated with δ. Most of the sources in our sample have τ of the order of days, which might be related to processes in the jet. We find marginal difference in the distribution of τ between FSRQs and BL Lacs.

VLT Optical Spectroscopy of BL Lac Objects

2006 ◽  
pp. 140-141
Author(s):  
B. Sbarufatti ◽  
A. Treves ◽  
R. Falomo ◽  
J. Heidt ◽  
J. Kotilainen ◽  
...  
Keyword(s):  
Optical Spectroscopy ◽  
Bl Lac Objects ◽  
Bl Lac

scholarly journals The FIRST-APM QSO Survey (FAQS) in the SBS Region. Current Status

2002 ◽  
Vol 184 ◽  
pp. 293-294
Author(s):  
V. Chavushyan ◽  
R. Mújica ◽  
J.R. Valdés ◽  
L. Carrasco ◽  
J. Stepanian ◽  
...  
Keyword(s):  
Emission Line ◽  
Seyfert Galaxies ◽  
Ongoing Study ◽  
Current Status ◽  
Complete Sample ◽  
Byurakan Survey ◽  
Bl Lac Objects ◽  
Bl Lac ◽  
Emission Line Galaxies ◽  
Overlapping Region

AbstractAs the first step of the Multiwavelength AGN Survey (MWAS), we have started the FIRST-APM QSO Survey (FAQS). The main goal of FAQS is to compile the most complete sample of bright QSOs, located in the area of the sky covered by the Second Byurakan Survey (SBS). Here we report the current status of an ongoing study based on the cross-identification of the FIRST radio catalog and the APM optical catalog. The overlapping sky area between FIRST and SBS is about 700 deg2. The compiled list of sources for this overlapping region contains ~ 400 quasar candidates brighter than . About 90 objects were already spectroscopically classified. During 1999-2000, we observed spectroscopically more than 150 FAQS objects with the 2.1m telescope of the Guillermo Haro Astropysical Observatory (GHAO). We have found 51 new QSOs (4 BAL QSOs), 13 Seyfert Galaxies (5 NLSyl’s), 23 emission line galaxies, 3 BL Lac objects and 57 stars.

scholarly journals Long-Term Optical Behavior of BL Lac Objects

1994 ◽  
Vol 159 ◽  
pp. 394-394
Author(s):  
S. Kikuchi
Keyword(s):  
Time Scale ◽  
Shock Model ◽  
Bl Lac Objects ◽  
Optical Photometry ◽  
Preferred Direction ◽  
Bl Lac ◽  
Direction Of Polarization ◽  
Optical Behavior

On the basis of results of optical photometry and polarimetry of OJ287 and Mrk421 since 1981, we find two states of activities for both objects. In OJ287, a color-magnitude relation which is consistent with the standard jet-shock model is seen after the outburst in 1983, while before 1982 the optical colors were almost constant. In Mrk421, the colors became redder in 1985–87, and the change of the preferred direction of polarization was associated on smaller time scale in 1987.

scholarly journals VHE BL Lacs through the MAGIC glasses

2014 ◽  
Vol 10 (S313) ◽  
pp. 64-69
Author(s):  
Josefa Becerra González ◽  
Keyword(s):  
Optical Emission ◽  
Theoretical Models ◽  
High Energy ◽  
Bl Lac Objects ◽  
Individual Object ◽  
Bl Lac ◽  
Multi Wavelength ◽  
Very High Energy ◽  
First Time

AbstractIn this contribution an overview of the latest results on the study of BL Lac objects with the MAGIC telescopes at the very high energy (VHE, E>100 GeV) gamma-rays is presented. Three new VHE sources were detected during 2014, two BL Lac objects and the gravitational lensed blazar S3 0218+357. MAGIC detected very fast intra-night variability from IC 310. This detection points to smaller emitting regions than the event horizon, this is hard to be explained in the framework of the current theoretical models. The long term multi wavelength (MWL) study of the BL Lac PKS 1424+240 shows correlation between the radio and optical emission, pointing to a common origin. The MWL SED is not well fitted by a one-zone synchrotron-self Compton (SSC) model, but a two-zone SSC model can explain both, the MWL light curve and the SED. Spectral curvature has been found in the observed VHE spectrum from PG 1553+113. This is the first time that spectral curvature compatible with the EBL absorption is found in an individual object.

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