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 (  >10) Doppler factor radio −S 5 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  Jy beam -1

5. 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

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 h igh velocity jet (Γ=15, θ=4 o (δ  15) in the  -ray region (< 0.02 pc) −one-sided jet confirms relativistic velocity out to 1” from the core −probably larger viewing angle (  =1 0 o -15 o ) 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  as rms ~ 1.5 mJy/beam core unresolved at 86 GHz −size smaller than 0.03 pc (gaussian fit) −M BH =10 9 M sun, 1 R S =10 -4 pc −radius ~ 300 R S −T B > 4 x 10 9 K S t =150 mJy, S c =45 mJy −limb brightening in core region? −10 mJy component @0.73 mas, PA 172 o 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  -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: 1.new mm-VLBI observations just obtained for Mrk501 (8/5/08) 2.mm-VLBI observations for 4 more blazars to take place next session (10/08) 3.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- 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!