The very flat radio spectrum of 0735 plus 178 - A cosmic conspiracy

Cotton, W. D.; Wittels, J. J.; Shapiro, I. I.; Marcaide, J. M.; Owen, F. N.; Spangler, S. R.; Rius, A.; Angulo, C.; Clark, T. A.; Knight, C. A.

doi:10.1086/183271

Cited by 77 publications

(55 citation statements)

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“…In two cases, a major long-term radio flux outburst occurs shortly after a mode change has appeared and this can be explained within the non-ballistic motion scenario of hotspots outlined in the previous subsection. In the optical emission, Fan et al (1997) and Qian & Tao (2004) found periodic features of 13.8-14.2 years. This is roughly twice the time interval we find here between the two mode transitions.…”

Section: Timescales: Flux-density Variability and Mode Changementioning

confidence: 97%

“…Extensive monitoring of this blazar in the radio and optical bands revealed variability on different timescales. Periodic features of 13.8-14.2 years were found by applying the Jurkevich method to about a century long optical monitoring data (Fan et al 1997;Qian & Tao 2004). A&A 515, A105 (2010) Ciprini et al (2007) reported possible detection of several shorter time scales.…”

Section: Introductionmentioning

confidence: 99%

“…In the radio band, an unusual property highlighted for this BL Lac is its remarkably flat radio spectrum, termed as "cosmic conspiracy" (Cotton et al 1980). …”

Section: Introductionmentioning

confidence: 99%

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Understanding BL Lacertae objects

Britzen¹,

Witzel²,

Gong

et al. 2010

A&A

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Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714 and report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. By analyzing the pc-scale jet morphology and its changes in 0735+178 we seek to understand the emission processes in BL Lac objects and to decipher their differences from quasars. A detailed study of the jet components' motion reveals that the standard AGN paradigm of apparent superluminal motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar motions in the jets of BL Lac objects as a class. Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2 cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Multiple Gaussians were fitted to the derived VLBA data, to trace the kinematical and flux density evolution of the individual VLBI (Very Long Baseline Interferometry) components in the nuclear jet. We then compared the jet kinematics with the optical and radio light curves available for this BL Lac object and point out some striking correlations between the properties of the radio knots and the features in the light curves. Results. We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape. We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an apparent superluminal motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic motions of the radio knots, produced by the precession of a continuous jet within the ambient medium. Conclusions. This is the third BL Lac object (after 1803+784 and 0716+714) analyzed by us, which reveals kinematic properties in the parsec-scale radio jet, which are atypical of quasars. For several years, the components in the jet are not found to be separating from the core but instead to be moving perpendicularly to the ridge line of the jet. In 0735+178 this unusual behavior has been particularly conspicuous. Curiously, however, fast apparent superluminal motion characteristic of quasars were present in this jet between the epochs ∼1995 and ∼2000. Thus we found for this BL Lac object a drastic change in the kinematics of the nucle...

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Section: Timescales: Flux-density Variability and Mode Changementioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Understanding BL Lacertae objects

Britzen¹,

Witzel²,

Gong

et al. 2010

A&A

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“…The only night with optical data is of modest quality and could be fit with a single power law. This source, however, is known from VLBI studies to be multicomponent on "large" (milliarc second) scales; this is the "cosmic conspiracy" source of Cotton et al 1980.…”

Section: Source Of the Spectral Variationsmentioning

confidence: 99%

0.35-3.5 micron photometry of blazars

Sitko

1991

PASP

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Thirty-one blazars were observed photometrically in the near-infrared, with additional observations in the optical for many of them. A few of them exhibit spectral behavior indicative of multiple emission components or emission processes. Six objects were also analyzed for any possible correlation between spectral steepness and luminosity. In one object, 0735 + 178, the spectral index a is correlated with the flux level with 99.9% confidence. Two other objects, 0846+513 and 0851+202, showed similar correlations at the 98% and 90% confidence levels, respectively. In all three cases the spectrum became flatter at higher flux levels. The data are consistent with expectations of models of inhomogeneous synchrotron models. In some cases, the self-Compton component may contribute significantly to the optical flux.Key words: quasars-photometry IntroductionThe blazars (BL Lacertae objects and optically violent variable (OVV) quasars) are active galactic nuclei whose emission is characterized by a nonthermal, variable, polarized flux, generally attributed to synchrotron radiation. The photon spectral shape is determined by the energy spectrum of the radiating particles. In its simplest form, the spectrum is nearly a power law with index a (with a defined as L v y 01 ) over a narrow frequency range, as expected for a parent population of particles (generally assumed to be electrons) whose energy spectrum is also a power law. In simple realistic models the spectra will turn down at low and high frequencies due to self-absorption, energy losses, and energy cutoffs in the particle population.While spectra have often been fit with such simple models, it has become increasingly clear that real sources Visiting Astronomer at the Mount Lemmon Observing Facility, operated by the University of Minnesota and the University of California at San Diego.Visiting Astronomer at Steward Observatory, operated by the University of Arizona.Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.Visiting Astronomer at the Infrared Telescope Facility, operated by the University of Hawaii under contract to the National Aeronautics and Space Administration.have photon spectra which are significantly curved, steepening toward higher frequencies (see, for example, Landau et al. 1986). Such curvature can be explained if the sources are inhomogeneous; the rate of steepening is related to the shape of the emitting region, generally thought to be the cone or funnel of a relativistic jet and the variations in particle energies and magnetic field strength along it.Königl 1981 and Ghisellini, Maraschi & Treves 1985 present results of inhomogeneous synchrotron selfCompton models in regions with jetlike geometries. In some combinations of jet geometry and particle-flow accelerations, the low-frequency and high-frequency (integrated) synchrotron fluxes come primarily from...

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“…The electrons give rise to the observed synchrotron spectrum at radio frequencies (e.g., Bridle & Perley 1984). Some AGN, however, show flat radio spectra, which are interpreted as self-absorbed synchrotron radiation of multiple jet knots (e.g., Cotton et al 1980). Several studies of radio and X-ray detected AGN have resulted in an apparent correlation between the radio and X-ray luminosities (e.g., Salvato et al 2004;Brinkmann et al 2000), suggesting a common physical origin of both phenomena.…”

Section: Introductionmentioning

confidence: 99%

Compact radio emission fromz ~ 0.2 X-ray bright AGN

Zuther

Fischer

Eckart

2012

A&A

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Context. The radio and X-ray emission of active galctic nuclei (AGN) appears to be correlated. The details of the underlying physical processes, however, are still not fully understood, i.e., to what extent the X-ray and radio emission is originating from the same relativistic particles, or from the accretion-disk, or corona, or both. Aims. We study the cm radio emission of an SDSS/ROSAT/FIRST matched sample of 13 X-raying AGN in the redshift range 0.11 ≤ z ≤ 0.37 at high angular resolution with the goal of searching for jet structures or diffuse, extended emission on sub-kpc scales. Methods. We used MERLIN at 18 cm for all objects and Western EVN at 18 cm for four objects to study the radio emission on scales of ∼500 pc and ∼40 pc for the MERLIN and EVN observations, respectively. Results. The detected emission is dominated by compact nuclear radio structures. We find no kpc collimated jet structures. The EVN data indicate compact nuclei on 40 pc scales, with brightness temperatures typical for accretion-disk scenarios. Comparison with FIRST data shows that the 18 cm emission is resolved out up to 50% by MERLIN. Star-formation rates based on large aperture SDSS spectra are generally too low to produce considerable contamination of the nuclear radio emission. We can, therefore, assume the 18 cm flux densities to be produced in the nuclei of the AGN. Together with the ROSAT soft X-ray luminosities and black-hole mass estimates from the literature, our sample objects closely follow the Merloni et al. fundamental plane relation, which appears to trace the accretion processes. Detailed X-ray spectral modeling from deeper hard X-ray observations and higher angular resolution at radio wavelengths are required to make more progress in separating jet and accretion related processes.

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The very flat radio spectrum of 0735 plus 178 - A cosmic conspiracy

Cited by 77 publications

References 0 publications

Understanding BL Lacertae objects

Understanding BL Lacertae objects

0.35-3.5 micron photometry of blazars

Compact radio emission fromz ~ 0.2 X-ray bright AGN

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