Previous lectures

1. 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.

2. 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?

3. ... 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!

4. 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...

5. 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.

6. Radio Variability

7. Radio Variability

8. 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?

9. ... 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.

10. ... Multifrequency (radio-submm) • Spectral indices. • Simultaneity of events. • Similarity of events. • Time delays between frequencies.

11. 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?”

12. ”Millimetre dilemma” 1 2 3 • 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.

13. ... well-known sources • Not necessarily representative of their class. • Cluster analysis: Many of the ”famous” sources are outliers.

14. ... ”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!

15. ... 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!)

16. Sometimes few-epoch observations can reveal the true (?) variability! (Time btw the 2 90 GHz data points = 14 years!)

17. Effect of sparse data taking:

18. Effect of sparse data taking:

19. 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!

20. 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?

21. 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

22. ... R/O connection

23. 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!

24. 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.

25. 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.

26. 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?

27. R/G connection: PKS 2255-282 Tornikoski et al. AJ 118, 1999

28. Identifying the EGRET-detections Tornikoski et al. ApJ 579, 2002

29. ... Identifying Tornikoski et al. ApJ 579, 2002

30. ... 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. Tornikoski et al. ApJ 579, 2002

31. Inverted-spectrum sources • GHz-peaked-spectrum (GPS) sources, in general: • nturnover > 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.

32. 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

33. Samples • “Bona fide GPS sources”. • GPS candidates. • “Sometimes inverted spectra”. • Comparison samples: GPS galaxies, CSS-galaxies. Southern sample + Northern sample Long-term, multifrequency data.

34. “Bona fide GPS sources”: With long-term monitoring very few retain the convexshape!

35. Effect of sparse data taking:

36. Only very few genuinely convex spectra!

37. 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!

38. Radio properties of BL Lacs,Intermediate BL Lacs (IBL) Original source sample: Veron-Cetty & Veron 2000: 462 BLOs • 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 theunifying scheme? Goals:

39. 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.

40. XBL

41. 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?

42. 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 the mm-domain probably larger than expected?