Evidence for cospatial optical and radio polarized emission in active galactic nuclei

Gabuzda, D. C.; Rastorgueva, E. A.; Smith, Paul S.; O’Sullivan, S. P.

doi:10.1111/j.1365-2966.2006.10433.x

Cited by 48 publications

(74 citation statements)

References 29 publications

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“…This discrepancy is likely due to the combination of the emergence of a new component, the Faraday rotation and the difference in beam size at the two frequencies. At the core, the Faraday rotation can be significant for BL Lacertae (Gabuzda et al 2006;Jorstad et al 2007), mostly affecting the 15.4 GHz measurements. It is also worth noting that the effects can be variable on timescales of months.…”

Section: Gamma-ray Propertiesmentioning

confidence: 99%

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

Arlen¹,

Aune²,

Beilicke³

et al. 2012

ApJ

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We report on the detection of a very rapid TeV gamma-ray flare from BL Lacertae on 2011 June 28 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The flaring activity was observed during a 34.6 minute exposure, when the integral flux above 200 GeV reached (3.4 ± 0.6) × 10 −6 photons m −2 s −1 , roughly 125% of the Crab Nebula flux measured by VERITAS. The light curve indicates that the observations missed the rising phase of the flare but covered a significant portion of the decaying phase. The exponential decay time was determined to be 13 ± 4 minutes, making it one of the most rapid gamma-ray flares seen from a TeV blazar. The gamma-ray spectrum of BL Lacertae during the flare was soft, with a photon index of 3.6 ± 0.4, which is in agreement with the measurement made previously by MAGIC in a lower flaring state. component from the core around the time of the TeV gamma-ray flare, accompanied by changes in the optical polarization angle. Changes in flux also appear to have occurred at optical, UV, and GeV gamma-ray wavelengths at the time of the flare, although they are difficult to quantify precisely due to sparse coverage. A strong flare was seen at radio wavelengths roughly four months later, which might be related to the gamma-ray flaring activities. We discuss the implications of these multiwavelength results.

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Section: Gamma-ray Propertiesmentioning

confidence: 99%

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

Arlen¹,

Aune²,

Beilicke³

et al. 2012

ApJ

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“…A connection between polarization and brightness is rarely seen at optical wavelengths (Smith 1996). However, there are strong indications that the optical polarized emission is linked to the millimeter-wave VLBI core of blazars jets ( Lister & Smith 2000;Gabuzda et al 2006;D'Arcangelo et al 2007;Jorstad et al 2007). …”

Section: Introductionmentioning

confidence: 99%

The Outburst of the Blazar AO 0235+164 in 2006 December: Shock‐in‐Jet Interpretation

Hagen-Thorn

Larionov

Jorstad

et al. 2008

ApJ

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We present the results of polarimetric (R-band) and multicolor photometric (BVRIJHK ) observations of the blazar AO 0235+16 during an outburst in 2006 December. The data reveal a short timescale of variability (several hours), which increases from optical to near-IR wavelengths; even shorter variations are detected in polarization. The flux density correlates with the degree of polarization, and at the maximum degree of polarization the electric vector tends to align with the parsec-scale jet direction. We find that a variable component with a steady power-law spectral energy distribution and very high optical polarization (30%Y50%) is responsible for the variability. We interpret these properties of the blazar within a model of a transverse shock propagating down the jet. In this case a small change in the viewing angle of the jet, by P1 , and a decrease in the shocked plasma compression by a factor of $1.5 are sufficient to account for the variability.

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“…If the optical emission and the radio emission both originate from the same physical region (which is often not easy to establish), then the radio EVPA should approach the optical EVPA at the shortest radio wavelengths. This appears to be the case for a sample of 12 blazars (mostly BL Lac objects) observed at 15 GHz, 22 GHz and 43 GHz [34]. At 15 GHz there is no radio-optical alignment at all.…”

Section: Optical Polarization and The Radio-optical Evpa Alignmentmentioning

confidence: 94%

Magnetic fields and polarization in AGN jets

Wardle

2013

EPJ Web of Conferences

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Abstract. In the literature there is now a wealth of images of AGN in both linear and circular polarization at milliarcsecond resolution of many sources at multiple epochs and wavelengths. This review is a broad overview of our current state of knowledge of the polarization properties of AGN jets, and of what we can infer about the structure of their magnetic fields and the distribution of Faraday rotating material, and also what is premature to infer. We suggest that while many of the observations of transverse rotation measure gradients may be correct, they have in general been observed with neither enough resolution nor sensitivity to be incontrovertible. Fortunately, this could be remedied using the new broad-band receivers on the VLBA. We also argue that while a transverse rotation measure gradient is a strong indicator of a toroidal component of magnetic field, it does not necessarily imply a helical magnetic field. In jets where the dominant field component appears to be parallel to the jet, it more likely consists of sheared loops or compressed random fields that are not vector ordered. Finally, we draw attention to the power of imaging in all four Stokes parameters at multiple frequencies to constrain the three-dimensional magnetic field structure and the particle content of jets and measure fundamental physical properties.

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Evidence for cospatial optical and radio polarized emission in active galactic nuclei

Cited by 48 publications

References 29 publications

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

The Outburst of the Blazar AO 0235+164 in 2006 December: Shock‐in‐Jet Interpretation

Magnetic fields and polarization in AGN jets

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