Optical Spectropolarimetry Observations of the BL Lac-type object PKS 0537-441 after a period of quiescence

We report on the discovery of a peculiar broad absorption line (BAL) quasar identified in our Gaia-assisted survey of red quasars. The systemic redshift of this quasar was difficult to establish because of the absence of conspicuous emission lines. Based on deep and broad BAL troughs of at least Si IV, C IV, and Al III, a redshift of z = 2.41 was established under the assumption that the systemic redshift can be inferred from the red edge of the BAL troughs. However, we observe a weak and spatially extended emission line at 4450 Å that is most likely due to Lyman-α emission, which implies a systemic redshift of z = 2.66 if correctly identified. There is also evidence for the onset of Lyman-α forest absorption bluewards of 4450 Å and evidence for Hα emission in the K band consistent with a systemic redshift of z = 2.66. If this redshift is correct, the quasar is an extreme example of a detached low-ionisation BAL quasar. The BALs must originate from material moving with very large velocities ranging from 22 000 km s−1 to 40 000 km s−1. To our knowledge, this is the first case of a systemic-redshift measurement based on extended Lyman-α emission for a BAL quasar. This method could also be useful in cases of sufficiently distant BL Lac quasars without systemic-redshift information.

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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.

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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.

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STUDY OF BL Lac VLBA DATA AT 8 AND 15 GHz IN A SUPER-RESOLUTION MODE

The Astrophysical Journal ◽

10.1088/0004-637x/705/1/877 ◽

2009 ◽

Vol 705 (1) ◽

pp. 877-884 ◽

Cited By ~ 6

Author(s):

Claudio E. Tateyama

Keyword(s):

Super Resolution ◽

Bl Lac

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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.

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Stochastic Modeling of Multiwavelength Variability of the Classical BL Lac Object OJ 287 on Timescales Ranging from Decades to Hours

The Astrophysical Journal ◽

10.3847/1538-4357/aad2de ◽

2018 ◽

Vol 863 (2) ◽

pp. 175 ◽

Cited By ~ 23

Author(s):

A. Goyal ◽

Ł. Stawarz ◽

S. Zola ◽

V. Marchenko ◽

M. Soida ◽

...

Keyword(s):

Stochastic Modeling ◽

Bl Lac ◽

Multiwavelength Variability

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The challenging SED of AP Librae

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312009532 ◽

2011 ◽

Vol 7 (S284) ◽

pp. 411-413 ◽

Cited By ~ 3

Author(s):

David Sanchez ◽

Berrie Giebels ◽

Pascal Fortin ◽

Keyword(s):

Spectral Energy Distribution ◽

Broad Band ◽

Low Frequency ◽

Theoretical Models ◽

Intermediate Frequency ◽

High Energy ◽

Spectral Energy ◽

Broad Band Emission ◽

Band Emission ◽

Bl Lac

AbstractMatching the broad-band emission of active galaxies with the predictions of theoretical models can be used to derive constraints on the properties of the emitting region and to probe the physical processes involved. AP Librae is the third low frequency peaked BL Lac (LBL) detected at very high energy (VHE, E>100GeV) by an Atmospheric Cherenkov Telescope; most VHE BL Lacs (34 out of 39) belong to the high-frequency and intermediate-frequency BL Lac classes (HBL and IBL). LBL objects tend to have a higher luminosity with lower peak frequencies than HBLs or IBLs. The characterization of their time-averaged spectral energy distribution is challenging for emission models such as synchrotron self-Compton (SSC) models.

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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.

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