New AGNs Discovered with the 2.16-m Telescope at Xinglong Station of Beijing Astronomical Observatory

Through combined ROSAT and VLA observations, we have identified 19 BL Lac/quasar candidates. In 1994 December, 1995 January and October, and 1996 January 1996, we obtained spectra of all 19 candidates using the 2.16-m telescope of Beijing Astronomical Observatory. The dispersion used is 195 Å mm−1, which yields a dispersion of about 4.65 Å pixel−1, and the wavelength coverage is 3500–7800 Å. Five of these objects are uniformly featureless, and we identify them as BL Lac objects. Three new quasars are also identified. Table 1 presents VLA positions and redshifts for the 5 new BL Lac objects and three new quasars. By checking them in the NASA/IPAC Extragalactic Database (NED) and Véron-Cetty & Véron’s (1993) Catalogue of Quasars and AGNs, and other recent reports about discovery of new BL Lac objects and quasars, we find that these sources are previously unreported.

Download Full-text

Coordinated Multifrequency Observations of OJ 287 and MK 421 (March 1993)

Symposium - International Astronomical Union ◽

10.1017/s007418090017593x ◽

1994 ◽

Vol 159 ◽

pp. 404-404

Author(s):

A. Sillanpää ◽

L.O. Takalo ◽

E. Valtaoja ◽

H. Teräsranta ◽

Yu.S. Efimov ◽

...

Keyword(s):

Weather Conditions ◽

Optical Observations ◽

Radio Observations ◽

Bl Lac Objects ◽

Preliminary Results ◽

La Palma ◽

Bl Lac ◽

Ccd Observations

We present some very preliminary results of the multifrequency microvariability campaign of two BL Lac objects OJ 287 and Mk 421 carried out mainly during four days in March 1993. During these four days also IUE was observing these blazars. In this poster we present only a small part of the whole data: radio observations at Metsähovi, CCD observations on La Palma and Heidelberg and UBVRI photopolarimetric observations at Crimea. Because of the very bad global weather conditions and also because of the faintnes of OJ 287 our optical observations were very limited.

Download Full-text

Deep Photography of Radio Sources with the Cambridge CCD System

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000016325 ◽

1981 ◽

Vol 4 (2) ◽

pp. 195-197

Author(s):

C. D. Mackay ◽

D. Astili ◽

M. J. Batty ◽

D. L. Jauncey ◽

A. E. Wright ◽

...

Keyword(s):

Radio Source ◽

Ccd Camera ◽

Radio Galaxies ◽

Detailed Examination ◽

Radio Sources ◽

Camera System ◽

Bl Lac Objects ◽

Charge Coupled Device ◽

Preliminary Results ◽

Bl Lac

We present preliminary results from a programme designed to produce deep images of radio source fields drawn from the Parkes 2700 MHz and Molongolo 408 MHz catalogues using the charge-coupled-device (CCD) camera system built at the Institute of Astronomy, Cambridge. The programme is directed at a search both for faint extensions and nebulosity around radio QSOs and BL Lac objects and for faint objects in otherwise empty radio source fields; a detailed examination of the morphology of selected radio galaxies is also included.

Download Full-text

A Comparison of the X-ray Spectra of Quasars and BL Lac Objects

Symposium - International Astronomical Union ◽

10.1017/s0074180900140811 ◽

1989 ◽

Vol 134 ◽

pp. 197-198

Author(s):

D. M. Worrall ◽

B. J. Wilkes

Keyword(s):

Power Law ◽

Radio Spectrum ◽

Spectral Indices ◽

Mean Power ◽

Bl Lac Objects ◽

X Ray ◽

Bl Lac ◽

Infrared Frequencies

Quasars with similar core-compact radio properties can be classified by their differences at optical and infrared frequencies. Their X-ray properties might be expected to be similar if the synchrotron self-Compton mechanism relates their radio and X-ray emission. We have compared the 0.2–3.5 keV mean power-law energy spectral indices, , for 4 quasar classes: 12 Highly Polarized QSOs (HPQs), 19 Flat Radio Spectrum, core-compact, low-polarization, QSOs (FRS QSOs), 24 radio-selected BL Lac objects, and 7 X-ray-selected BL Lac objects.

Download Full-text

The Environment of OJ 287: Nearby Galaxies and a Long Optical Jet?

Symposium - International Astronomical Union ◽

10.1017/s0074180900079961 ◽

1996 ◽

Vol 175 ◽

pp. 47-48

Author(s):

A. Sillanpää ◽

L. Takalo ◽

K. Nilsson ◽

T. Pursimo ◽

P. Teerikorpi ◽

...

Keyword(s):

Large Scale ◽

Radio Galaxies ◽

Trigger Mechanism ◽

Galaxy Clustering ◽

Bl Lac Objects ◽

Close Interaction ◽

Relativistic Jet ◽

Bl Lac ◽

Nearby Galaxies ◽

Bl Lacs

A widely accepted model for BL Lac objects is that they are radio galaxies with a relativistic jet pointing almost directly towards us. But we need a clear trigger mechanism for these jets. One possibility is the close interaction between the BL Lac host and the closeby galaxies (e.g. Heckman et al. 1986). This interaction has been seen many times in the case of quasars (Hutchings et al. 1989) but not so much is known about the close surroundings of the BL Lac objects although there has been some pioneer work like Stickel et al. (1993). The problem has usually been that the images are not deep enough and that the seeing has not been so good. To clarify the situation we have started an observing program to get very deep images in the sub-arcsecond seeing conditions from the whole 1 Jy sample (Stickel et al. 1991) of BL Lac objects. The aims of this study are: 1. to search for very close companions to the BL Lacs, 2. to study the large scale galaxy clustering around the BL Lacs and 3. to study the BL Lac hosts themselves.

Download Full-text

Serendipitous VLBI Observations of Intraday Variability in the BL Lac Objects 1334–127, 2131–021, and 2155–152

International Astronomical Union Colloquium ◽

10.1017/s0252921100045528 ◽

1998 ◽

Vol 164 ◽

pp. 273-274

Author(s):

P. Yu. Kochanev ◽

D. C. Gabuzda

Keyword(s):

Rapid Variability ◽

Bl Lac Objects ◽

Polarization Structure ◽

Vlbi Observations ◽

Bl Lac ◽

Vlbi Data ◽

Intraday Variability

AbstractGlobal λ = 6 cm VLBI polarization observations of intraday variability in the three BLLacertae objects 1334–127, 2131–021, and 2155–152 are analyzed. Integrated VLA measurements during the VLBI observations show that although there were no substantial total intensity variations, the polarizations for these three sources varied significantly during the VLBI experiment. The VLBI data were divided into 2-3 hour segments in order to search for corresponding rapid variability in the VLBI polarization structure. Our analysis shows that the VLA polarization variability in 2155–152 and 2131–021 is present in the VLBI data (i.e., it occurred on mas scales), but this is not the case for 1334–127.

Download Full-text

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629419 ◽

2017 ◽

Vol 598 ◽

pp. A39 ◽

Cited By ~ 20

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.

Download Full-text