sub-parsec scale properties of the TeV blazar Mrk 501

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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
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Outline

• Introduction
• Observations results
• High sensitivity HSA
• High resolution VSOP1 Global mm-VLBI Array
• Open questions perspectives
• Summary

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Markarian 501

• BL Lac _at_ z 0.034, HBL
• high energy
• detected by EGRET and TeV Cherenkov
• highly active/variable
• SSC models require high (dgt10) Doppler factor
• radio
• S5 GHz 1 Jy
• VLA two sided
• pc scales one sided-jet, twisting

Albert et al. 2007
Cassaro et al. 1999
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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

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Increase in sensitivty means

1. VLBA snapshot
2. Deep Space VLBI
3. Our new data not only a beautiful image but also
   rich of information
4. 3000 increase in number of pixels above noise

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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 (G15, ?4o (d?15) in the g-ray region (lt
  0.02 pc)
• one-sided jet confirms relativistic velocity out
  to 1 from the core
• probably larger viewing angle (q10o-15o) and
  slower velocity (G10, d?2.6)

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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

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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
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high res by higher frequency mm-VLBI

• VLBA ok _at_43 GHz, not adequate _at_86
• the Global mm VLBI array operates _at_3mm with
  larger dishes and longer baselines (VLBAIRAM
  telescopesEbOnMh)
• resolution 0.05 mas
• still not very sensitve (0.1-0.4 Jy)...
• ...but enough to detect Mrk501

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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)
• MBH109 Msun, 1 RS10-4 pc
• radius 300 RS
• TB gt 4 x 109 K
• St150 mJy, Sc45 mJy
• limb brightening in core region?
• 10 mJy component _at_0.73 mas, PA 172o
• cleaning, model fitting, self-calibration
  difficult

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GMVA obs of Mrk 501 results

• steep high frequency spectrum, turnover _at_ 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
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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

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VLBI observations perspectives

• sub-parsec scale structure
• new mm-VLBI observations just obtained for Mrk501
  (8/5/08)
• mm-VLBI observations for 4 more blazars to 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

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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!