The QSO 1156+295 - A multifrequency study of recent activity

Wills, Beverley J.; Pollock, J. T.; Aller, H. D.; Aller, M. F.; Balonek, T. J.; Barvainis, Richard; Binzel, R. P.; Chaffee, F. H.; Dent, W. A.; Douglas, James N.; Fanti, C.; Garrett, D. B.; Gregorini, L.; Henry, R. B. C.; Hill, Ryley; Howard, R. A.; Jeske, N.; Kepler, S. O.; Leacock, R. J.; Mantovani, F.; O’Dea, C. P.; Padrielli, L.; Perley, P.; Pica, A. J.; Puschell, J. J.; Sanduleak, N.; Shields, G. A.; Smith, Alex; Thuan, T. X.; Wade, C. M.; Wasilewski, A. J.; Webb, J. R.; Wills, D.; Wisniewski, W. Z.

doi:10.1086/161426

Cited by 45 publications

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“…In the optical bands, 1156+295 shows rapid variations on timescales of between less than 30 min and 3 days (Wills et al 1983;Raiteri et al 1998). The first IDV detection of 1156+295 at radio frequencies was reported by Lovell et al (2003), who observed the source with the VLA at 5 GHz in January 2002.…”

Section: Introductionmentioning

confidence: 99%

“…Kovalev et al 2002). Wills et al (1983) reported a range of at least 5 mag in the optical brightness, and in gamma-rays Sreekumar et al (1996) detected an order of magnitude variability using the EGRET instrument onboard the Compton Gamma Ray Observatory. During high radio brightness states, 1156+295 appears to be highly core-dominated in VLBI images (95% at some epochs, Kovalev et al 2005; see also ranging from 3.5 h −1 c to 14.1 h −1 c were reported by e.g.…”

Section: Introductionmentioning

confidence: 99%

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Serendipitous VLBI detection of rapid, large-amplitude, intraday variability in QSO 1156+295

Savolainen

Kovalev

2008

A&A

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Aims. We report a serendipitous detection of rapid, large amplitude flux density variations in the highly core-dominated, flat-spectrum radio quasar 1156+295 during an observing session at the Very Long Baseline Array (VLBA). Methods. The source was observed as a part of the MOJAVE survey programme with the VLBA at 15 GHz on February 5, 2007. Large amplitude variability in the correlated flux density, unexplainable in terms of the source structure, was first discovered while processing the data, and later confirmed by calibrating the antenna gains using 24 other sources observed in the experiment. Results. The source shows variations in the correlated flux density as high as 40% on a timescale of only 2.7 h. This places 1156+295 between the classical IDV sources and the so-called intra-hour variables. The observed variability timescale and the modulation index of 13% are consistent with interstellar scintillation by a nearby, highly turbulent scattering screen. The large modulation index at 15 GHz implies a scattering measure that is atypically high for a high galactic latitude source such as 1156+295.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Serendipitous VLBI detection of rapid, large-amplitude, intraday variability in QSO 1156+295

Savolainen

Kovalev

2008

A&A

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“…Strong γ-ray flares have been detected by EGRET and Fermi at energies higher than 100 MeV (Thompson et al 1995;Mukherjee et al 1997;Hartman et al 1999;Abdo et al 2009). In the optical domain, the source has been classified as an optically violent variable (OVV) source and highly polarized quasar (HPQ) (Wills et al 1983(Wills et al , 1992Glassgold et al 1983). In the radio domain, 1156+295 displays a significant variability on timescales from years to days (e.g.…”

Section: Introductionmentioning

confidence: 99%

Radio structure of the blazar 1156 + 295 with sub-pc resolution

Zhao

Hong

et al. 2011

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Aims. 1156+295 is a flat-spectrum quasar that is loud at both radio and γ-ray wavelengths. Previous observations of the source revealed a radio morphology on pc to kpc scales consistent with a helical jet model. We carried out VLBA observations at centimeter and millimeter wavelengths to study the structure of the innermost jet and understand the relation between the helical structure and astrophysical processes in the central engine. Results. A core-jet structure with six jet components is identified in 1156+295. Three jet components are detected for the first time. The apparent transverse velocities of the six jet components derived from proper motion measurements range between 3.6 c and 11.6 c, suggesting that highly relativistic jet plasma moves in the direction close to the line of sight. The overall jet has an oscillating morphology with multiple curvatures on pc scales, which might be indicative of a helical pattern. Models of a helical jet are discussed in the context of both Kelvin-Helmholtz (K-H) instability and jet precession. The K-H instability model is in closer agreement with the observed data. Conclusions. The overall radio structure on scales from sub-pc to kpc appears to be fitted with a hydrodynamic model in the fundamental helical mode of Kelvin-Helmholtz (K-H) instability. This helical mode with an initial characteristic wavelength of λ 0 = 0.2 pc is excited at the base of the jet on the scale of 0.005 pc (or 10 3 R s , the typical size of the broad line region of a supermassive black hole of 4.3 × 10 8 M ). A precessing jet model can also fit the observed jet structure on scales of between 10 pc and 300 pc. However, with the precessing jet model, additional astrophysical processes may be required to explain the bendings of the inner jet structure (1 to 10 pc) and re-collimation of the large-scale jet outflow (>300 pc).

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“…Table 1 is also available in machine-readable form in the electronic edition of the Astronomical Journal. (e.g., Wills et al 1983) and (2) partly because many of these objects are intrinsically different from classical quasars, as shown by their diffuse radio emission, which is similar to that of an FR I radio galaxy (e.g., Kollgaard et al 1992;Rector & Stocke 2001). These two effects cannot be clearly separated using only VLBI data.…”

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confidence: 99%

Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine-Scale Structure

et al. 2005

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We have examined the compact structure in 250 flat-spectrum extragalactic radio sources using interferometric fringe visibilities obtained with the Very Long Baseline Array ( VLBA) at 15 GHz. With projected baselines out to 440 Mk, we are able to investigate source structure on typical angular scales as small as 0.05 mas. This scale is similar to the resolution of the VLBI Space Observatory Programme data obtained on longer baselines at a lower frequency and with somewhat poorer accuracy. For 171 sources in our sample, more than half of the total flux density seen by the VLBA remains unresolved on the longest baselines. There are 163 sources in our list with a median correlated flux density at 15 GHz in excess of 0.5 Jy on the longest baselines; these will be useful as fringe finders for shortwavelength VLBA observations. The total flux densities recovered in the VLBA images at 15 GHz are generally close to the values measured around the same epoch at the same frequency with the RATAN-600 and University of Michigan Radio Astronomy Observatory telescopes.We have modeled the core of each source with an elliptical Gaussian component. For about 60% of the sources, we have at least one observation in which the core component appears unresolved (generally smaller than 0.05 mas) in one direction, usually transverse to the direction into which the jet extends. BL Lac objects are on average more compact than quasars, while active galaxies are on average less compact. Also, in an active galaxy the submilliarcsecond core component tends to be less dominant. Intraday variability (IDV) sources typically have a more compact, more core-dominated structure on sub-milliarcsecond scales than non-IDV sources, and sources with a greater amplitude of intraday variations tend to have a greater unresolved VLBA flux density. The objects known to be GeV gamma-ray-loud appear to have a more compact VLBA structure than the other sources in our sample. This suggests that the mechanisms for the production of gamma-ray emission and for the generation of compact radio synchrotron-emitting features are related. The brightness temperature estimates and lower limits for the cores in our sample typically range between 10 11 and 10 13 K, but they extend up to 5 ; 10 13 K, apparently in excess of the equipartition brightness temperature or the inverse Compton limit for stationary synchrotron sources. The largest component speeds are observed in radio sources with high observed brightness temperatures, as would be expected from relativistic beaming. Longer baselines, which can be obtained by space VLBI observations, will be needed to resolve the most compact high brightness temperature regions in these sources.

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The QSO 1156+295 - A multifrequency study of recent activity

Cited by 45 publications

References 0 publications

Serendipitous VLBI detection of rapid, large-amplitude, intraday variability in QSO 1156+295

Serendipitous VLBI detection of rapid, large-amplitude, intraday variability in QSO 1156+295

Radio structure of the blazar 1156 + 295 with sub-pc resolution

Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine-Scale Structure

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