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The jet of Mrk 501 from millions of Schwarzschild radii down to a few hundreds

The jet of Mrk 501 from millions of Schwarzschild radii down to a few hundreds. Marcello Giroletti INAF Istituto di Radioastronomia and G. Giovannini, G. Taylor, B. Cotton M.Perez Torres, P. Edwards, M. Chiaberge. Outline. Introduction Observations & results High sensitivity: HSA

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The jet of Mrk 501 from millions of Schwarzschild radii down to a few hundreds

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  1. The jet of Mrk 501 from millions of Schwarzschild radii down to a few hundreds Marcello Giroletti INAF Istituto di Radioastronomia and G. Giovannini, G. Taylor, B. Cotton M.Perez Torres, P. Edwards, M. Chiaberge

  2. Outline • Introduction • Observations & results • High sensitivity: HSA • High resolution: VSOP1 & Global mm-VLBI Array • Open questions & perspectives • Summary

  3. Markarian 501 • BL Lac @ z = 0.034, HBL • high energy: • detected by EGRET and TeV Cherenkov • highly active/variable • SSC models require high (d>10) Doppler factor • radio • S5 GHz = 1 Jy • VLA: two sided • pc scales: one sided-jet, twisting Albert et al. 2007 Cassaro et al. 1999

  4. High Sensitivity Array (HSA) • The High Sensitivity Array: • VLBA (10x25m) • phased VLA (27x25m) • Arecibo (300m) • Green Bank (110m) • Effelsberg (100m) • 7x more sensitive than the VLBA alone! • Our observations: • 8 hrs, 1.6 GHz (optically thin regime), large recording rate (256 Mbps) • final rms noise: 25 mJy beam-1

  5. VLBA snapshot Deep Space VLBI Ournewdata: not only a beautiful image but also rich of information 3000% increase in number of pixels above noise Increase in sensitivty means…

  6. HSA: the jet velocity structure • transverse: • slice at 100 mas from core is limb brightened • two velocity regime? • radial • SED/high energy emission require high velocity jet (Γ=15, θ=4o (δ15) in the g-ray region (< 0.02 pc) • one-sided jet confirms relativistic velocity out to 1” from the core • probably larger viewing angle (q=10o-15o) and slower velocity (Γ=10, δ2.6)

  7. HSA: the magnetic field structure • magnetic field structure • polarized intensity as high as 100 mJy/beam • organized magnetic field • B stratified in the inner jet, perpendicular to jet axis after the bend • from adiabatic model: consistent with polarization, requires high initial velocity • helix: intriguing but inconsistent with predictions

  8. high res by long baselines: Space VLBI • compact structures are resolved in higher resolution images • no proper motion over 9 epochs • similar to other TeV blazars • limb brightening clearly revealed by VSOP • interpreted in terms of velocity structure: fast inner spine, slower external shear • intermediate viewing angle • important for theoretical jet models • where is its origin? • need even better resolution! Giroletti et al. 2004

  9. high res by higher frequency: mm-VLBI • VLBA ok @43 GHz, not adequate @86 • the Global mm VLBI array operates @3mm with larger dishes and longer baselines (VLBA+IRAM telescopes+Eb+On+Mh) • resolution ~0.05 mas • still not very sensitve (0.1-0.4 Jy)... • ...but enough to detect Mrk501

  10. GMVA obs of Mrk 501: results • resolution ~110 x 40 mas • rms ~ 1.5 mJy/beam • core unresolved at 86 GHz • size smaller than 0.03 pc (gaussian fit) • MBH=109 Msun, 1 RS=10-4 pc • radius ~ 300 RS • TB > 4 x 109 K • St=150 mJy, Sc=45 mJy • limb brightening in core region? • 10 mJy component @0.73 mas, PA 172o • cleaning, model fitting, self-calibration difficult

  11. GMVA obs of Mrk 501: results • steep high frequency spectrum, turnover @ ~8 GHz • magnetic field in the range 0.01 – 0.03 G • structure within the “core” • starting velocity and acceleration? • constraints from g-ray emission? GLAST, AGILE • jet structure • did we eventually find a "real" jet knot? • orientation, limb brightening seem to be in agreement with VLBA at 43 GHz Marscher et al. 2002

  12. VLBI obs of Mrk 501: open questions • 1) is limb brightened structure real? • need better sensitivity and (u,v) coverage • 2) is spectrum really optically thin? • need more accurate amplitude calibration and (possibly) resolution • 3) what is the magnetic field structure? • need sensitivity and polarimetry • 4) what do other blazars look like? • need sensitivity and ease of use

  13. VLBI observations: perspectives • sub-parsec scale structure: • new mm-VLBI observations just obtainedfor Mrk501 (8/5/08) • mm-VLBI observations for 4 more blazarsto take place next session (10/08) • VSOP2 (launch 2012) will be the key… • connection to high-energy activity: • waiting for GLAST, AGILE results • Medicina and Noto radio telescopes participated in recent multi-l campaign

  14. take home notes • mrk 501 interesting source • twisting jet, one vs. two sided structure, TeV source • high resolution and sensitivity essential • HSA: perpendicular B field • VSOP1 successful: limb brightening, resolved components • mm-VLBI detection ok, but open questions remain • VSOP2, GLAST needed • also for many more sources!

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