Multifrequency Polarization Variations in 0917+624

AbstractIntraday variability in compact flat-spectrum radio sources has been intensively studied in recent years. For most IDV events the apparent brightness temperatures derived from the observed timescales are in the range of Tb,app ~ 1016−18 K. For extremely rapid variations, Tb,app can reach up to ~ 1021 K (e.g. Kedziora-Chudczer et al., 1997). Refractive interstellar scintillation may be the most likely extrinsic mechanism (Rickett et al., 1995; Qian, 1994a; Qian, 1994b). Especially for the case of extreme Tb,app (> 1018 K) RISS may be dominant (Dennet-Thorpe and de Bruyn, 2000). However, some IDV events with Tapp ~ 1017−18 K show evidence for an intrinsic origin e.g. the correlated radio-optical intraday variations observed in the BL Lac object 0716+714 (Wagner and Witzel, 1995, Qian et al, 1996). It seems important to distinguish between IDV which is a phenomenon intrinsic to the compact radio sources and IDV which is primarily due to RISS. Multifrequency polarization and VLB I observations would be most helpful (Gabuzda and Kochanev, 1997).

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Multi-Frequency Studies of Intrinsic Intraday Variability

International Astronomical Union Colloquium ◽

10.1017/s0252921100000798 ◽

2001 ◽

Vol 182 ◽

pp. 105-111

Author(s):

Stefan J. Wagner

Keyword(s):

Electromagnetic Spectrum ◽

Potential Contribution ◽

Bl Lac Objects ◽

High Brightness ◽

Brightness Temperatures ◽

Interstellar Scintillation ◽

Bl Lac ◽

Radio Wavelength ◽

Very High ◽

Intraday Variability

AbstractIntraday variability is detected in Blazars throughout the electromagnetic spectrum. Only radio emission is affected by interstellar scintillation. The characteristics of variability observed at different frequencies are often similar and suggest that intrinsic variations also contribute to the changes detected in the radio wavelength regime. This in turn implies very high brightness temperatures.Unambiguous signatures of scintillation and of intrinsic changes have been identified. The properties of intrinsic variations are reviewed to illustrate their potential contribution to variability in the radio domain. Such intrinsic changes need to be discriminated against when studying scintillation in quasars and BL Lac objects. Observations of scintillating sources and of sources with significant intrinsic IDV suggest interesting modifications to the standard paradigm of AGN.

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Superluminal Gravitational Microlensing Events In PKS 0537-441 And Prospects For Future Detections

Symposium - International Astronomical Union ◽

10.1017/s0074180900231495 ◽

1996 ◽

Vol 173 ◽

pp. 265-266

Author(s):

G.C. Surpi ◽

G.E. Romero ◽

H. Vucetich

Keyword(s):

Time Scales ◽

Alternative Explanation ◽

Compact Objects ◽

Systematic Search ◽

Apparent Brightness ◽

Brightness Temperatures ◽

Gravitational Microlensing ◽

Bl Lac ◽

Intraday Variability

The BL-Lac object PKS 0537-441 has recently displayed strong intraday variability at 1.42 GHz on time scales of ∼ 104 s. Such kind of variability is hardly consistent with an intrinsic-to-source origin, since apparent brightness temperatures higher than 1021 K are implied for the emitting region in the source.An alternative explanation for this ultra-rapid radio variability in PKS 0537-441 is developed based on gravitational microlensing of a superluminal component in the blazar caused by compact objects in the halo of an intervening galaxy. The mass of the microlenses is estimated and the blazar is proposed as a good candidate in a systematic search for extragalactic MACHOs.

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Bulk Relativistic Motion in a Complete Sample of Radio Selected AGN

Symposium - International Astronomical Union ◽

10.1017/s007418090015524x ◽

1987 ◽

Vol 121 ◽

pp. 287-293

Author(s):

C.J. Schalinski ◽

P. Biermann ◽

A. Eckart ◽

K.J. Johnston ◽

T.Ph. Krichbaum ◽

...

Keyword(s):

Dynamic Range ◽

Radio Sources ◽

Relativistic Motion ◽

Complete Sample ◽

Superluminal Motion ◽

Spectrum Radio ◽

Wide Range ◽

Show Evidence

A complete sample of 13 flat spectrum radio sources is investigated over a wide range of frequencies and spatial resolutions. SSC-calculations lead to the prediction of bulk relativistic motion in all sources. So far 6 out of 7 sources observed with sufficient dynamic range by means of VLBI show evidence for apparent superluminal motion.

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Interstellar Scintillation and Intraday Variability

International Astronomical Union Colloquium ◽

10.1017/s0252921100045504 ◽

1998 ◽

Vol 164 ◽

pp. 269-270

Author(s):

Barney J. Rickett

Keyword(s):

Intrinsic Variability ◽

Brightness Temperatures ◽

Interstellar Scintillation ◽

Intraday Variability

AbstractSources that are compact enough to show intrinsic variability on times of a day or less (IDV) at cm wavelengths must also show interstellar scintillation (ISS) on similar timescales. However for many IDV sources, the variations could be entirely due to ISS, reducing the implied brightness temperatures to ~ 1013 K or less.

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Intraday Variability in Northern Hemisphere Radio Sources

Publications of the Astronomical Society of Australia ◽

10.1071/as01085 ◽

2002 ◽

Vol 19 (1) ◽

pp. 14-18 ◽

Cited By ~ 28

Author(s):

T. P. Krichbaum ◽

A. Kraus ◽

L. Fuhrmann ◽

G. Cimò ◽

A. Witzel

Keyword(s):

Flux Density ◽

Radio Telescope ◽

Physical Interpretation ◽

Radio Sources ◽

Intrinsic Variability ◽

The Past ◽

Interstellar Scintillation ◽

Variability Pattern ◽

Complex Source ◽

Intraday Variability

AbstractWe summarise results from flux density monitoring campaigns performed with the 100 m radio telescope at Effelsberg and the VLA during the past 15 yrs. We briefly discuss some of the statistical properties from now more than 40 high declination sources (δ ≥ 30°), which show intraday variability (IDV). In general, IDV is more pronounced for sources with flat radio spectra and compact VLBI structures. For 0917+62, we present new VLBI images which suggest that the variability pattern is modified by the occurrence of new jet components. For 0716+71, we show the first detection of IDV at millimetre wavelengths (32 GHz). For the physical interpretation of the IDV phenomenon, a complex source and frequency dependent superposition of interstellar scintillation and source intrinsic variability should be considered.

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Extreme intra-hour variability of the radio source J1402+5347 discovered with Apertif

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038378 ◽

2020 ◽

Vol 641 ◽

pp. L4

Author(s):

T. A. Oosterloo ◽

H. K. Vedantham ◽

A. M. Kutkin ◽

E. A. K. Adams ◽

B. Adebahr ◽

...

Keyword(s):

Angular Size ◽

Oort Cloud ◽

Minor Axis ◽

Radio Sources ◽

Radio Waves ◽

Apparent Brightness ◽

Isotropic Source ◽

Interstellar Scintillation ◽

Interstellar Plasma ◽

Apparent Brightness Temperature

The propagation of radio waves from distant compact radio sources through turbulent interstellar plasma in our Galaxy causes these sources to twinkle, a phenomenon called interstellar scintillation. Such scintillations are a unique probe of the micro-arcsecond structure of radio sources as well as of the sub-AU-scale structure of the Galactic interstellar medium. Weak scintillations (i.e. an intensity modulation of a few percent) on timescales of a few days or longer are commonly seen at centimetre wavelengths and are thought to result from the line-of-sight integrated turbulence in the interstellar plasma of the Milky Way. So far, only three sources were known that show more extreme variations, with modulations at the level of some dozen percent on timescales shorter than an hour. This requires propagation through nearby (d ≲ 10 pc) anomalously dense (ne ∼ 102 cm−3) plasma clouds. Here we report the discovery with Apertif of a source (J1402+5347) showing extreme (∼50%) and rapid variations on a timescale of just 6.5 min in the decimetre band (1.4 GHz). The spatial scintillation pattern is highly anisotropic, with a semi-minor axis of about 20 000 km. The canonical theory of refractive scintillation constrains the scattering plasma to be within the Oort cloud. The sightline to J1402+5347, however, passes unusually close to the B3 star Alkaid (η UMa) at a distance of 32 pc. If the scintillations are associated with Alkaid, then the angular size of J1402+5347 along the minor axis of the scintels must be smaller than ≈10 μas, yielding an apparent brightness temperature for an isotropic source of ≳1014 K.

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Quasar Surveys

Symposium - International Astronomical Union ◽

10.1017/s0074180900152179 ◽

1986 ◽

Vol 119 ◽

pp. 17-32

Author(s):

M. G. Smith

Keyword(s):

Luminosity Function ◽

Seyfert Galaxies ◽

Radio Sources ◽

Selection Effects ◽

Spectral Evolution ◽

X Ray ◽

Spectrum Radio ◽

Show Evidence ◽

Optical Surveys ◽

Radio Luminosity Function

A review is given of progress in surveys for quasars at frequencies from radio to x-ray. Radio results show evidence for a decline in the radio luminosity function for flat-spectrum radio sources at redshifts z > 2. The IRAS survey is uncovering hitherto unknown dusty Seyfert galaxies. Optical surveys, which yield the largest number of QSOs per square degree, may suffer from selection effects which depend on intrinsic luminosity, redshift, and spectral evolution - particularly above redshift 2. Below redshifts of about 2.3, the optical magnitude-redshift plane is being filled in to the point where the evolution of the luminosity function can be seen directly. The statistics of quasar pair separations provide the best evidence so far for quasar clustering.The existence of many potentially significant selection effects means that a multi-frequency approach to quasar surveys is likely to prove essential to an understanding of the evolutionary behaviour of the quasar population as a whole.

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Intraday Variability and Microarcsecond Structure in Blazar Cores

Symposium - International Astronomical Union ◽

10.1017/s0074180900220524 ◽

2001 ◽

Vol 205 ◽

pp. 84-87 ◽

Cited By ~ 2

Author(s):

David L. Jauncey ◽

Lucyna Kedziora-Chudczer ◽

J. E. J. Lovell ◽

Jean-Pierre Macquart ◽

George D. Nicolson ◽

...

Keyword(s):

William Shakespeare ◽

Brightness Temperature ◽

Circular Polarization ◽

Julius Caesar ◽

Principal Mechanism ◽

High Brightness ◽

Brightness Temperatures ◽

Interstellar Scintillation ◽

Intraday Variability

The accumulation of evidence now strongly favours interstellar scintillation (ISS) as the principal mechanism causing intra-day variability (IDV) at cm wavelengths. While ISS reduces the implied brightness temperatures, they remain uncomfortably high. The distance to the scattering screen is an important parameter in determining the actual brightness temperature encountered. The high brightness temperatures, the presence of strong and variable circular polarization and the observed lifetimes of a decade or more for several IDV sources, pose significant problems for synchrotron theory. “The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” William Shakespeare, Julius Caesar

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Examples of Extreme Intraday Variability

International Astronomical Union Colloquium ◽

10.1017/s0252921100000804 ◽

2001 ◽

Vol 182 ◽

pp. 113-117

Author(s):

Lucyna Kedziora-Chudczer ◽

David L. Jauncey ◽

Mark A. Wieringa ◽

Anastasios K. Tzioumis ◽

Hayley E. Bignall

Keyword(s):

Flux Density ◽

Density Fluctuations ◽

Total Flux ◽

Radio Sources ◽

Extragalactic Radio Sources ◽

Brightness Temperatures ◽

Relativistic Beaming ◽

Intraday Variability

AbstractWe present results of the ATCA IDV Survey of southern extragalactic radio sources. We discuss briefly the properties of the 22 new intraday variable sources discovered in the Survey. The follow-up observations of a few extreme examples of strong intraday variability are presented. We find that the characteristics of the total flux density fluctuations at different wavelengths are consistent with intersteller scintillations (ISS) of the microarcsecondsize soorten components. However, the scintillating components of a few extreme IDVs are characterized by the brightness temperatures far exceeding the TB = 1012 K limit. The relativistic beaming invoked in such sources would require Doppler factors up to as high as δ ~ 103.

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