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TeV/X-ray correlated variability in Blazars

(optical, radio). TeV/X-ray correlated variability in Blazars. Robert Wagner Max-Planck-Institut für Physik, Munich & Excellence Cluster “Origin & Structure of the Universe”, Munich. Blazars. q. x100. Most extreme class of AGNs known

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TeV/X-ray correlated variability in Blazars

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  1. (optical, radio) TeV/X-ray correlated variability in Blazars Robert Wagner Max-Planck-Institut für Physik, Munich & Excellence Cluster “Origin & Structure of the Universe”, Munich R. Wagner – Correlations between the two radiative populations in blazars

  2. Blazars q x100 • Most extreme class of AGNs known • Appear to emit bulk bolometric luminosity in g–ray band • High variability • Dominated by non-thermal emission • Two well-defined components • Synchrotron emission by relativistic electrons in the jet (emission patterns, polarization, ...) • IC emission from the same electrons (Rees 84, Urry+Padovani 95) Wehrle+98   Electron Electron • In particular in blazars: Synchrotron Self-Compton model: synchrotron photons target field for IC process • Natural explanation of X-ray / -ray correlated variability  • Protons:0 decay from photo-pion production, secondary e– or synchrotron emission from protons • Difficult to accomodate X-ray / -ray correlations • Expect to observe simultaneous -emission R. Wagner – Correlations between the two radiative populations in blazars

  3. TeV Blazars • 6 HBLs known in 2002 • Mkn 421, Mkn 501, 1ES 2344+514, PKS 2155–304, 1ES 1959+650, H 1426+428 • Now well studied, well sampled, monitoring/MWL ongoing • Interesting laboratories: • HBL Spectrum almost featureless • jet environment poor in soft photons • HE emission produced by Comptonization of synchrotron radiation: SSC • Possibility of observing emission by VHE electrons g~107 coupled with X-ray observation • More generally: IC at g-ray energies – photons • from the jet, • from emission-line clouds, • from a dusty torus, • from some other external source R. Wagner – Correlations between the two radiative populations in blazars

  4. SSC Framework • Simultaneous studies in X and TeV bands • In SSC X and TeV should be closely correlated: Being produced by electrons of similar energies • Assume B~0.1G, d~10: • 1 keV photons emitted by electrons with g~106. • Same electrons will upscatter photons at E ~ gmc ~ 1TeV • Standard parameters: IC in KN. Thompson regime would require rather high D factors • SSC: Expect Simultaneous variability or slight lags for low-frequencies (accomodated by forward/reverse shocks) (Sokolov+04) • Quadratic correlation difficult if flare decay goverend by cooling of emitting electrons; seed  cool on longer timescale and IC-  should trace electron cooling Washed-out correlations • Gradients in the highest electron energies • Superposition/Pile-up of rising & decaying flares • Different energy electrons populate different volumes • Peak reached earlier at higher frequencies due to optical thickness (Marscher 04) R. Wagner – Correlations between the two radiative populations in blazars

  5. Merits & Caveats • Correlation between X-ray and g-ray emission may provide important information on the emission mechanism + physical mechanism producing variability • Need to compare two different light curves • Obtained in the same period • By two different instruments • Sampling rate for instruments must be similar • Short variability timescales in HBLs: dense sampling! • Additional spectral information needed to understand spectral evolution: X-ray sampling below or above Sy peak?? • Just a few cases where correlation can be studied reliably and in detail R. Wagner – Correlations between the two radiative populations in blazars

  6. Observed correlations Katarzynski+05 • Significant evidence of correlated variability: • Buckley+96 Mkn 421 1995 April 20 to May 5 • Catanese+97 Mkn 501 1997 April 8 to April 19 • Correlated & Simultaneous flares from Mkn 421 (Maraschi+99, Fossati+04,08), Mkn 501 (Sambruna+00) • Weeks to months (Krawczynski+00, Blazejowski+05, Gliozzi+05) • Results confirmed on other occasions • But: Correlation absent in some cases: • “orphan“ TeV flares in 1ES 1959+650 (Krawczynski+04) • Orphan TeV flares & Childless X-ray flares in Mkn 421 R. Wagner – Correlations between the two radiative populations in blazars

  7. Comprehensive Studies • Comprehensive Study: Time-Dependent Analysis still missing! 2-month time-dependent modeling: Krawczynski+02 for Mkn 501, but rather sparse sampling • Investigate case of a Homogeneous SSC model: Katarzynski+05 • Week-long study for 2001 Mkn 421:Fossati+08 R. Wagner – Correlations between the two radiative populations in blazars

  8. Mkn 501 flare in 1997 April Catanese+97 Katarzynski+05 • Catanese+97: • Whipple>350 GeV, • OSSE 50-150 keV, • ASM 3-20 keV • Needed to interpolate Whipple, ASM data, resp. • Correlation is • Fg~Fx1.7±0.5 for OSSE, • Fg~Fx2.7±0.6 for ASM, • Fg~Fx1.0...2.0 for 0.1-200 keV BeppoSAX (Djannati-Atai+99) • Correlated optical variability • Caveats! Correlation may depend on • Position of spectral bands used • Width of spectral band • Krawczynski+00, Mkn 501 in 1997: • Quadratic corr. 3-25 keV/2TeV (cf. ASM) R. Wagner – Correlations between the two radiative populations in blazars

  9. Krawczynski+01 Katarzynski+05 Mkn 421 in 2000 February • Krawczynski+01: • HEGRA>1TeV, • PCA 3-20 keV, • ASM 3-20 keV • Needed to interpolate HEGRA data. • Correlation is • Fg~Fx0.5±0.2, poor c² (PCA), inconclusive • Long-timescale observations, albeit with poor sampling • One data point per day only R. Wagner – Correlations between the two radiative populations in blazars

  10. Mkn 421 in 2001 March Fossati+04,07,08 • Precise observations, 1 week, dense sampling • Whipple, HEGRA (uninterrupted coverage in spring!) • PCA 3-20 keV • 62 hrs/7 nights R. Wagner – Correlations between the two radiative populations in blazars

  11. Mkn 421 in 2001 March Fossati+ 08 • Generally no lags seen • Flare on March 19 PCA/Whipple • High amplitude: Likely to see undiluted flare • High correlation coefficient, r=0.8 • Lag of 2 ks for g-rays w.r.t. soft X-rays • Zero lag for hard X-rays R. Wagner – Correlations between the two radiative populations in blazars

  12. Mkn 421 in 2001 March Fossati+ 08 TeV vs various X-ray bands • 105 data pairs • Clear correlation seen for all X-ray bands (2-60 keV) • Approx linear correlation, also for day-averages (see later) R. Wagner – Correlations between the two radiative populations in blazars

  13. Day-by-day correlations Fossati+ 08 • Day-by-day averages follow trend, linear • Regions covered nightly shift from day to day, quadratic correlations. • Correlations on sub-day and day-scale differ! • Flare Pile-up, superimposed rise and decay phases? • Or two luminosity-related regimes...? R. Wagner – Correlations between the two radiative populations in blazars

  14. Mkn 421 in 2001 March Fossati+ 08 Split to high-flux and medium-flux days: Significantly steeper for flare days • Flare on March 19: TeV-X correlation almost quadratic for rising and decay phase (Note: full flare evolution covered) • Overall Whipple-PCA Correlation is Fg~Fx1.3±0.1 • Long-Term correlation differs from flare correlation • Tanihata+04, Mkn 421 1wk in 1998: • Fg~Fx1.7±0.1, at Syn peak position Day 1+2 Day 5-7 R. Wagner – Correlations between the two radiative populations in blazars

  15. Long-Term: Mkn 421 2003-4 Blazejowski+05 • Regular obs during dark time, 28 min/night, with more runs on occasion • 306 runs • Plus optical, radio R. Wagner – Correlations between the two radiative populations in blazars

  16. Not always in step? Blazejowski+05 • Rough correlation, but dynamical range ~30 in both energy bands • Broad spectral coverage, but still • Correlation more loose than expected • Rather wide PCA/Whipple bandsno observational artifact Mkn 421, 2003/4 X leads g, 1.8±0.4 days, marginal 2002/3 2003/4 Including MJD 53100 outburst R. Wagner – Correlations between the two radiative populations in blazars

  17. Not always in step? Blazejowski+05 • X reaches peak 1.5 dbefore VHE R. Wagner – Correlations between the two radiative populations in blazars

  18. SSC Model Tests Katarzynski+05 • Spherical homogeneous source, may undergo expansion/compression, density change, magnetic field, adiabatic cooling Src expands, B and  const Sy, IC ~ volume R, B const, and  incr. Sy ~ volume, IC ~ vol x Sy R. Wagner – Correlations between the two radiative populations in blazars

  19. Between the peaks Katarzynski+05 Expanding spherical homogeneous source Change of spectral index of high-energy part of electron spectrum Included radiative coolingof electrons R. Wagner – Correlations between the two radiative populations in blazars

  20. Quinn+99 Aharonian+02 Gliozzi+06 Long-term variability: Mkn 501 • General positive trend, but: • Rather large scatter: Presence of uncorrelated activity • Data point 11 s off • Sampling: every 3..4 days during longer periods • “Contemporaneous data“: not more than 8 hrs apart X-rays TeV R. Wagner – Correlations between the two radiative populations in blazars

  21. Quinn+99 Aharonian+02 Gliozzi+06 Long-term variability: Mkn 501 • Look at individual periods: Heterogeneous behavior • May 97: Linear Fg~Fx0.99±0.01 • June 98: Quadratic Fg~Fx2.07±0.36 X-rays • Individual flares: • X-ray flux >4 in < 1 week • TeV activity differs TeV Krawczynski+02 Time-dependent modeling: need 2 components R. Wagner – Correlations between the two radiative populations in blazars

  22. Long-term variability: M87 Acciari+08 • Close, misaligned blazar • Locus of  radiation: Close to BH vs. HST-1? Radio HST-1 knot A knot D X-ray nucleus VLBA 8 GHz Chandra X-rays Harris+07 R. Wagner – Correlations between the two radiative populations in blazars

  23. Long-term variability: M87 Acciari+08 • HST-1 flare not seen in ASM • Soft spectrum • r=0.780.11 • Core more likely to be VHE source if correlation is real R. Wagner – Correlations between the two radiative populations in blazars

  24. Strong flares from 1ES 1959+650 • Optical, RXTE-PCA, Whipple • General correlation,“orphan flare“ sticks out • Tight correlation between 3-25 keV spectral index and 10 keV flux Krawczynski+04 R. Wagner – Correlations between the two radiative populations in blazars

  25. 1ES 1959+650: The Orphan Flare Case Krawczynski+04 • TeV flare without obvious X-ray couterpart • But: SSC flare ~ 15 days before • Similar cases observed for Mkn 421 • (2003/4 campaign) • True orphan flare? Might lag behindits X-ray counterpart? • Too sparse sampling? Blazejowski+05 R. Wagner – Correlations between the two radiative populations in blazars

  26. 1ES 1959+650: The Orphan Flare Case Krawczynski+04, Böttcher 2005, Reimer+05 • BLR clould as mirror and subsequent secondary flare from pg-interactions R. Wagner – Correlations between the two radiative populations in blazars

  27. Experimental Resolution • Very short X-ray flares, not always coincident with TeV flares Blazejowski+05 Aharonian+07 • A new hope: Resolution of TeV telescopes Albert+07 Mkn 501 PKS 2155-304 R. Wagner – Correlations between the two radiative populations in blazars

  28. Recent campaigns: PKS 2155-304 MWL Oct 19-Nov 26, 2003, Aharonian+05 Strictly overlapping data No correlation seen PKS 2155-304, 2004 r = 0.71±0.05 Giebels 07 R. Wagner – Correlations between the two radiative populations in blazars

  29. Recent campaigns: Mkn 501 Mkn 501, day-by-day 2005 Dominated by large ASM errors (MAGIC/RXTE underway) Albert+07 R. Wagner – Correlations between the two radiative populations in blazars

  30. Recent campaigns: 1ES 2344+514 Horan+08 Oct 07-Jan 08 VERITAS/PCA R. Wagner – Correlations between the two radiative populations in blazars

  31. Recent campaigns: Mkn 421 Reyes+08 Albert+07 14 p airs / 14 hrs Jan/Feb 08 VERITAS/PCA/Swift XRT Nov04-Apr05 MAGIC/ASM 13 nights Six consecutive Nights Apr05 R. Wagner – Correlations between the two radiative populations in blazars

  32. Optical correlation? 1ES 1959+650, Krawczynski+04 No obvious correlation in 1ES 1959+650, Mkn 501 (Petry+00, Albert+07), Mkn 421 (Giebels+07), PKS 2155-304 (Aharonian+05) Fractional Variability Power-law compatible Mkn 421 (Giebels+07) BL Lac, Albert+07 R. Wagner – Correlations between the two radiative populations in blazars Second source after Mkn 180 for which an optical trigger proved successful.

  33. Do Optical Triggers Work? Albert+ 07a,b Trigger point Mkn 180 1ES 1011+496 Trigger point MAGIC 18.7 h S=6.2  R. Wagner – Correlations between the two radiative populations in blazars BL Lacertae? Cannot claim correlation yet. Second source after Mkn 180 for which an optical trigger proved successful.

  34. Some conclusions • Generally, correlated variability is observed • On time-scales of hours to months (... to years?) • With all possible experimental caveats: time and spectral coverage, evidence for co-spatiality • Same electron distribution? Same physical region? • Connection of TeV activity & VLBI core variability (22 GHz radio as self-absorbed SSC counterpart,Charlot+06, Mkn 421, 1998 March-April) • With all possible observational caveats: Lags, orphan, and childless flares, pile-up. • What about • VHE-Optical correlation? • VHE-Radio correlation? R. Wagner – Correlations between the two radiative populations in blazars

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