Merja Tornikoski Metsähovi Radio Observatory Previous lectures Fundamentals of radio astronomy –Flux, brightness temperature... –Antennae, surface accuracy,

Merja TornikoskiMetsähovi Radio Observatory

Previous lectures

• Fundamentals of radio astronomy– Flux, brightness temperature...– Antennae, surface accuracy, antenna temperature...– Signal & noise, detecting a weak signal.– Some general considerations.

• Blazar observing techniques– Receivers for microwave/mm/submm domains.– Bolometers, bolometer arrays.– Point source observations, techniques.– Pointing, focusing, calibration.– Telescope performance, things to pay attention to.– From observation into a data point.– From an idea into an (sub)mm-observing proposal.


Variability studies• Different kind of variability behaviour at different frequency

domains.• Different kind of variability behaviour at different (radio)

frequencies.• Correlating and non-correlating events:

different emission mechanisms?• What we want to know...

– The details of the various emission mechanisms improved shock models, improved quasar models.

– Are all the variations at one frequency region in one object created in the same way?

– What is the relationship between variability observed at various frequency domains?

– What are the fundamental differences betw. different objects?


... Variability studies• What we need:

– Multifrequency data with good temporal sampling.– High-resolution (space-)VLBI.

• The real world of the observational (radio) astronomer is far from the ideal world!


Radio Variability Studies

• Frequent flux density monitoring:– UMRAO: 4.8, 8.0, 14.5 GHz– Metsähovi: 22, 37 (+ 87) GHz– (SEST: 90, 230 GHz)

• Other observatories with flux density mesasurements:– HartRAO, RATAN-600, Itapetinga,, IRAM, JCMT...


Radio Variability

• Centimeter/millimeter continuum studies:– Amplitudes and timescales of variability– Time delays between frequencies Testing and developing the shock + jet models.

• VLBI studies: – Maps at mas scales, superluminal components.

• Together: – Parsec-scale relativistic jets:

jet parameters and jet dynamics (jet orientation, flow speeds)

– Shocks in the jets: growth and decay of radio outbursts, superposed radio flare components, etc.


Radio Variability

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Radio Variability

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What we get

• ”Only fluxes”.• Data for variability studies:

– Physical parameters from timescales etc.– How do flares grow and decay?.

• Data for multifreqeuency science:– Emission mechanisms.– Where are flares produced?– How are the various em domains connected?

• Studies of different kinds of AGNs:– Fundamental differences in source populations.– Unification schemes.– The true number of radio-bright sources?


... Multi-epoch

• Smin, Smax, Save.

• Variability indices.• Flare amplitudes.• Timescales: flare rise & decay times, flare occurance rates.

• ”Variability brightness temperature” Tb,obs(var)+ estimates for Doppler boosting, Lorentz factors etc.(Lähteenmäki et al. ApJ 511, 112, 1999; ApJ 521, 493, 1999).

• Flare models shock models.


... Multifrequency (radio-submm)

• Spectral indices.• Simultaneity of events.• Similarity of events.• Time delays between frequencies.


Variability

• Individual flares in individual sources Related to theoretical work:Models & Parameters.– e.g. Valtaoja 1999; Lähteenmäki & Valtaoja 1999;

Türler et al. 2000

• Observational statistics:”What are we likely to see?” and ”How often?”


”Millimetre dilemma”

• Very limited availability of telescope time.

Focus on well-known, bright, variable sources.

Sources that are assumed to be faint are usually ignored / excluded.

Conclusions often based on few-epoch (or even one-epoch!) observations.

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... well-known sources

• Not necessarily representative of their class.

• Cluster analysis: Many of the ”famous” sources are outliers.


... ”faint” sources

• Source selection for mm-studies often based on (few-epoch) low-frequency catalog data.

• Many interesting sources or even source populations are excluded from mm-studies!


... few epochs

• At 90 GHz, a random obsevation is likely to see an AGN in a quiescent or intermediate state! (At 230 GHz,even more so!)


Sometimesfew-epoch observationscan reveal the true (?)variability!(Time btw the 290 GHz data points = 14 years!)


Effect of sparse data taking:




VLBI

• Does not resolve the core/jet – Future space VLBI?

• Does not (yet) routinely use high frequency.– 2mm/150 GHz experiment

Pico Veleta – Metsähovi — SEST,May 2001.

• Often does not have good time resolution.

High-frequency monitoring needed!


Radio variability models

• Current situation:– A lot of data: high-f, mf, dense sampling, long time series...– "Quiescent" state: jet spectrum.

Variability from outbursts, sometimes (often??) several superposed components.

– Flare behaviour at various radio frequencies relatively well understood.

– Qualitatively similar behavior (mostly ) in all blazars.– Also explains simultaneity (sometimes) of R & O outbursts.– More realistic physical models needed:

to include MHD; to explain the growth of the shock; to explain IDV; also to include jet geometry and disturbances, varying Doppler boosting etc.

– Connections to other f-domains?


Multifrequency studies:Radio / Optical connection

• Optical emission can be of thermal or non-thermal origin and can originate from several different locations.

• What is the emission mechanism in R/O flares (all non-thermal?).

• In what kind of sources do we see it?• When R/O, when only O?• What are the typical features of

an R/O flare?• Can we predict it?

Tornikoski et al., A&A 286, 1994


... R/O connection

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R/O predictions

• When O is correlated to R (with short time lags!), the O originates from the same synchrotron shock as R.– O should occur simultaneously with mm-flares, before cm-flares.

– In the beginning the polarisation increases, should reach its maximum when the flux reaches its maximum.

• Possible also: correlated events with very long time lags (optical precursory to radio), difficult to investigate!


R/O problems

• Gaps in data (esp. O).• (Probably) also non-correlating (optical) events.• Very different timescales.• Discrete sampling, different number of data points.• Changes in the base (“quiescent”) level.• Effects of prominent flares in the analysis.


Multifrequency studies:Radio / Gamma -connection

• Spectral energy distributions.• Correlation between radio

and gamma-ray activity.• Gamma-ray emission mechanisms.• New identifications

for unidentified EGRET gamma-ray sources.


Gamma-ray emission in AGNs

• Mechanism(s)? • Location(s)?• Can all blazars be gamma-bright?• Can all AGNs be gamma-bright?• Why are some sources only sometimes gamma-bright?• Why do only some sources seem to be gamma-bright?• What are the unidentified gamma-ray sources?


R/G connection: PKS 2255-282

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230 GHz

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Tornikoski et al. AJ 118, 1999


Identifying the EGRET-detections

Tornikoski et al. ApJ 579, 2002


... Identifying



... Identifying

5 to 90 GHz radio spectra for two new candidates for EGRET-identifications.Both of them show a rising spectrum towards the millimeter-domain (to the right), which is exceptional for ”normal” AGNs, but which is often seen in EGRET-detected AGNs.The source in the left panel is a possible identification for the EGRET-source 2EGS 1703-6302, and the one in the right panel, J1605-1139, is a possible identification for 3EG J1607-1101.



Inverted-spectrum sources

• GHz-peaked-spectrum (GPS) sources, in general:

turnover > 1 GHz.

– Compact.– GPS+CSS: the least variable

class of compact extragal. objects.– Low optical polarization.– Superluminal motion appears to be rare.– GPS sources identified with QSOs have large

z’s.


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Our work: objectives

• Part of the Planck foreground science programme.

• Variability of known GPS sources.

• New GPS sources.

• Extreme-peaked sources.

• Variable flat-spectrum vs.“genuine” GPS sources.

• VLBI structure of high-peaked sources.

Tornikoski et al. A&A 120, 2000


Samples

• “Bona fide GPS sources”.• GPS candidates.• “Sometimes inverted spectra”.

• Comparison samples: GPS galaxies, CSS-galaxies.

Southern sample + Northern sampleLong-term, multifrequency data.


“Bona fide GPS sources”:With long-term monitoring very few retain the convex shape!




Only very few genuinely convex spectra!


Torniainen & Tornikoski, in preparation for the A&A:

Lots of sources with spectra inverted during flares!

• Considerable variability in the mm-domain.• Turnover frequencies as high as >100 GHz.• During quiescent state the spectra remain flat

or even falling.• Probably a large number of such sources

have been excluded from high-frequency studiesand thus have not been identified yet!

• Note: much less time is spent in the active state!


• Systematically study the mm-properties of BLOs.• Is there a continuity from subsample to subsample?• Are there radio silent BLOs?• Can radio weak BLOs be radio loud at times?• How does this all fit within the framework of the

unifying scheme?

Original source sample: Veron-Cetty & Veron 2000: 462 BLOs

Radio properties of BL Lacs,Intermediate BL Lacs (IBL)

Goals:


Results• By July 2003: Observed 385 out of 398

equatorial to Northern BLOs = 96.7%.• For many of them, only one-epoch so far!• 37 GHz detection limit ca. 0.3 Jy.• Detections:

ALL: 130 / 385; 34%RBL: 49 / 56; 88%IBL: 41/125; 33%XBL: 28 / 103; 27%

Note: Some objects do not belong to any of the subclasses,sometimes several classifications are assigned to one object.


XBL


BLO -- conclusions

• More than 1/3 of all objects, ca. 1/3 of XBLs detected (S > 250-300 mJy) in one- or few-epoch observations.( detectable also with Planck-satellite!)

• Several highly inverted spectra.• Variability?


GPS + BLO -- Conclusions• Only very few genuinely convex spectra.• Lots of sources with spectra that can

sometimes be inverted, many of them arefaint at low radio frequencies.

• A large number of sources that can be bright in the mm-domain have earlier been excluded from source samples.

Number of AGNs that can be bright in themm-domain probably larger than expected?



Documents

Merja Tornikoski Metsähovi Radio Observatory Previous lectures Fundamentals of radio astronomy –Flux, brightness temperature... –Antennae, surface accuracy,