MOJAVE - Blazar monitoring with the VLBA

MOJAVE - Blazar monitoring with the VLBA

Tuomas Savolainen
LOFAR TKP Meeting, Amsterdam, June 2011

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transientskp

June 17, 2012
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  1. MOJAVE – Blazar monitoring MOJAVE – Blazar monitoring with the

    VLBA with the VLBA Tuomas Savolainen* Tuomas Savolainen* on behalf of the MOJAVE team on behalf of the MOJAVE team *Max-Planck-Institut f. Radioastronomie *Max-Planck-Institut f. Radioastronomie
  2. MOJAVE Collaboration MOJAVE Collaboration • M. Lister (P.I.), T. Hovatta

    M. Lister (P.I.), T. Hovatta (Purdue) • T. Savolainen, J. A. Zensus, T. Arshakian T. Savolainen, J. A. Zensus, T. Arshakian (MPIfR) • M. and H. Aller M. and H. Aller (Michigan) • M. Cohen M. Cohen (Caltech) • D. Homan D. Homan (Denison) • M. Kadler M. Kadler (Uni. Würzburg) • K. Kellermann K. Kellermann (NRAO) • Y. Kovalev Y. Kovalev (ASC Lebedev) • A. Pushkarev A. Pushkarev (Crimea) • E. Ros E. Ros (Uni. Valencia) • R. Vermeulen R. Vermeulen (ASTRON) www.physics.purdue.edu/astro/MOJAVE/ Very Long Baseline Array
  3. Blazars – a short reminder Blazars – a short reminder

    Image courtesy of A. Marscher Image courtesy of A. Marscher
  4. Blazars – a short reminder Blazars – a short reminder

    3C 273 (Savolainen et al. 2008) 3C 273 (Savolainen et al. 2008) Image courtesy of C. Fromm Image courtesy of C. Fromm 1. synchrotron self-absorption causes frequency-dependent shift of the core! 2. mm/cm wavelength variability likely due to shocks – at low frequencies they behave like expanding plasma bubbles
  5. MOJAVE program MOJAVE program • Studying the long term structural

    evolution of pc scale jets in Studying the long term structural evolution of pc scale jets in over 300 AGN at 15 GHz over 300 AGN at 15 GHz • mas-resolution, high-quality full Stokes images from VLBA mas-resolution, high-quality full Stokes images from VLBA • statistical studies of the jet kinematics statistical studies of the jet kinematics • multi-wavelength analysis incl. gamma-rays, X-rays, other multi-wavelength analysis incl. gamma-rays, X-rays, other radio observations radio observations • data since mid-1990s → allows analysis of complicated jet data since mid-1990s → allows analysis of complicated jet kinematics (accelerations, deforming components etc) kinematics (accelerations, deforming components etc) • Began in 1994 as VLBA 2cm Survey – approved until 2013 Began in 1994 as VLBA 2cm Survey – approved until 2013 • Includes 2 Includes 2 complete flux-limited AGN samples selected on the complete flux-limited AGN samples selected on the basis of basis of • compact radio emission (mostly blazars) compact radio emission (mostly blazars) • bright gamma-ray emission (again blazars) bright gamma-ray emission (again blazars) • Calibrated data is made public Calibrated data is made public
  6. Scientific goals of MOJAVE Scientific goals of MOJAVE Understanding jet

    physics Understanding jet physics • What is the overall distribution of superluminal speeds and What is the overall distribution of superluminal speeds and intrinsic velocities in AGN jets? intrinsic velocities in AGN jets? • Where do the jets get accelerated and collimated? Where do the jets get accelerated and collimated? • Do different components within a jet follow the same or different Do different components within a jet follow the same or different trajectories? Role of instabilities? Precession? trajectories? Role of instabilities? Precession? • Are there differences between the bulk flow velocity and the Are there differences between the bulk flow velocity and the pattern velocity? pattern velocity? • What is the nature of the material responsible for altering the What is the nature of the material responsible for altering the polarization properties of the jet emission? polarization properties of the jet emission? • By what mechanism is circularly polarized emission produced in By what mechanism is circularly polarized emission produced in AGN jets? AGN jets? • How are the gamma-ray emission and jet activity correlated? How are the gamma-ray emission and jet activity correlated?
  7. MOJAVE sample(s) MOJAVE sample(s) • MOJAVE-1 MOJAVE-1 • a complete

    sample of the 135 sources above decl. of -20deg that had a complete sample of the 135 sources above decl. of -20deg that had compact compact 15 GHz flux > 1.5 Jy anytime in 1994-2004 15 GHz flux > 1.5 Jy anytime in 1994-2004 • maps and kinematics published until 2007 (Lister et al. 2009) maps and kinematics published until 2007 (Lister et al. 2009) • MOJAVE-1.5 MOJAVE-1.5 • Extension of MOJAVE-1, currently 172 sources Extension of MOJAVE-1, currently 172 sources • all sources above decl. of -30deg that had >1.5 Jy anytime in 1994.0-2011.0 all sources above decl. of -30deg that had >1.5 Jy anytime in 1994.0-2011.0 • 1FM 1FM • selection criteria: 1FGL median energy flux (>100Mev) larger than 3x10^-11 selection criteria: 1FGL median energy flux (>100Mev) larger than 3x10^-11 erg s^-1 cm^-2, decl. >-30deg, |b|>10deg, no galactic sources or grav. erg s^-1 cm^-2, decl. >-30deg, |b|>10deg, no galactic sources or grav. lenses lenses • MOJAVE-2 list MOJAVE-2 list • Union of all the above plus some additional sources: 10 EGRET blazars, 22 Union of all the above plus some additional sources: 10 EGRET blazars, 22 low-luminosity AGN, 7 GPS/CSS, 6 peculiar sources from 2cm Survey, 20 low-luminosity AGN, 7 GPS/CSS, 6 peculiar sources from 2cm Survey, 20 Fermi flaring sources... Fermi flaring sources... • Currently 304 AGN Currently 304 AGN
  8. Observing strategy Observing strategy • VLBA at 15 GHz →

    ~0.6 mas VLBA at 15 GHz → ~0.6 mas resolution, can track jet resolution, can track jet features up to 10-20 mas features up to 10-20 mas • Full polarization imaging Full polarization imaging • One 24-hour session every One 24-hour session every ~3 weeks ~3 weeks • 30 sources per session 30 sources per session • Adaptive observing cadences Adaptive observing cadences • New Fermi sources added at New Fermi sources added at rate of one per 3-4 months rate of one per 3-4 months • Calibrated data posted to our Calibrated data posted to our website 1-2 months after website 1-2 months after observation. observation.
  9. None
  10. MOJAVE and LOFAR Transients? MOJAVE and LOFAR Transients? Questions Questions

    1) 1) What flux variability mechanisms might be What flux variability mechanisms might be present in blazars at LOFAR frequencies? present in blazars at LOFAR frequencies? 2) 2) What kind of information MOJAVE may provide What kind of information MOJAVE may provide for interpreting this variability? for interpreting this variability? 3) 3) Follow-ups within the MOJAVE program? Follow-ups within the MOJAVE program?
  11. Variability mechanisms Variability mechanisms (hints from the 408MHz monitoring by

    the Bologna group in the (hints from the 408MHz monitoring by the Bologna group in the 1980s and 1990s; Padrielli et al. 1987, Spangler et al. 1989, 1980s and 1990s; Padrielli et al. 1987, Spangler et al. 1989, Mantovani et al. 1990, Bondi et al. 1996) Mantovani et al. 1990, Bondi et al. 1996) 1) 1) Decaying shocks → Decaying shocks → correlated variability with correlated variability with cm-wavelengths albeit with cm-wavelengths albeit with large delays and decreased large delays and decreased amplitudes amplitudes → →MOJAVE can tell if a new MOJAVE can tell if a new shock was ejected before shock was ejected before the flare at low frequencies the flare at low frequencies (UMRAO and F-GAMMA (UMRAO and F-GAMMA data are also useful) data are also useful)
  12. Variability mechanisms Variability mechanisms 2) 2) Interstellar scintillation Interstellar scintillation

    (unless scatter broadening (unless scatter broadening due to IGM quenches it) due to IGM quenches it) • can be totally can be totally uncorrelated with cm- uncorrelated with cm- flaring flaring • however, MOJAVE could however, MOJAVE could • help to characterize the help to characterize the scintillating population scintillating population • if variability pattern if variability pattern changes, see if this due changes, see if this due to a new compact to a new compact component in the jet component in the jet
  13. Variability mechanisms Variability mechanisms 3) 3) More exotic mechanisms like

    coherent More exotic mechanisms like coherent emission in the beginning of the flare emission in the beginning of the flare → → this could happen before anything is observed this could happen before anything is observed at cm-wavelengths at cm-wavelengths → → triggering follow-up with cm-VLBI triggering follow-up with cm-VLBI → → if the source is in the MOJAVE list, cadence if the source is in the MOJAVE list, cadence can be adjusted → follow-up observations within can be adjusted → follow-up observations within 1-3 weeks (MoU needed) 1-3 weeks (MoU needed) → → if a very exceptional event is detected, a new if a very exceptional event is detected, a new source could be in principle added to MOJAVE source could be in principle added to MOJAVE monitoring – however requires green light from monitoring – however requires green light from both the PI and NRAO (MoU needed) both the PI and NRAO (MoU needed)
  14. Thank you

  15. Some recent results Some recent results • Kinematics of 526

    features in 127 jets Kinematics of 526 features in 127 jets ( (Lister et al. 2009 Lister et al. 2009) ) • Jets seem to have characteristic speeds Jets seem to have characteristic speeds • Speed distribution peaks at 10c and goes Speed distribution peaks at 10c and goes up to 50c → maximum blazar up to 50c → maximum blazar Γ Γ ~ 50 ~ 50 • Jet acceleration Jet acceleration (Homan et al. 2009) (Homan et al. 2009) • 1/3 components accelerate and 1/3 components accelerate and accelerations parallel to jet are larger → accelerations parallel to jet are larger → real changes in flow speed real changes in flow speed • more positive acceleration within 15 pc more positive acceleration within 15 pc from the core from the core
  16. Fermi Fermi Gamma-ray Space Telescope Gamma-ray Space Telescope and MOJAVE

    and MOJAVE There is a connection between VLBI jet properties and gamma-ray There is a connection between VLBI jet properties and gamma-ray brightness in AGN. See Lister et al. 2009, Kovalev et al. 2009, brightness in AGN. See Lister et al. 2009, Kovalev et al. 2009, Pushkarev et al. 2009, Savolainen et al. 2010, Pushkarev et al. 2010... Pushkarev et al. 2009, Savolainen et al. 2010, Pushkarev et al. 2010...
  17. None